M. Spencer Internet-Draft Digium, Inc. Intended status: Informational B. Capouch Expires: October 17, 2007 Saint Joseph's College E. Guy, Ed. TruPhone F. Miller Cornfed Systems, Inc. K. Shumard April 15, 2007 IAX2: Inter-Asterisk eXchange Version 2 draft-guy-iax-03 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. This document may not be modified, and derivative works of it may not be created. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on October 17, 2007. Copyright Notice Copyright (C) The IETF Trust (2007). Spencer, et al. Expires October 17, 2007 [Page 1] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 Abstract This document describes the Inter-Asterisk eXchange protocol, Version 2, (IAX2) an application-layer control and media protocol for creating, modifying, and terminating multimedia sessions over Internet Protocol (IP) networks. IAX2 was developed by the open source community for the Asterisk PBX and is targeted primarily at Voice over Internet Protocol (VoIP) call control, but it can be used with streaming video or any other type of multimedia. IAX2 is an "all in one" protocol for handling multimedia in IP networks. It combines both control and media services in the same protocol. In addition, IAX2 uses a single UDP data stream on a static port greatly simplifying Network Address Translation (NAT) gateway traversal, eliminating the need for other protocols to work around NAT, and simplifying network and firewall management. IAX2 employs a compact encoding which decreases bandwidth usage and is well suited for Internet telephony service. In addition, its open nature permits new payload types additions needed to support additional services. Spencer, et al. Expires October 17, 2007 [Page 2] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 7 1.1. Basic Properties . . . . . . . . . . . . . . . . . . . . 7 1.2. Drawbacks . . . . . . . . . . . . . . . . . . . . . . . . 8 2. IAX2 Terminology . . . . . . . . . . . . . . . . . . . . . . 9 3. Overview of IAX2 Protocol . . . . . . . . . . . . . . . . . . 10 4. Naming Conventions . . . . . . . . . . . . . . . . . . . . . 12 5. IAX2 Uniform Resource Identifiers . . . . . . . . . . . . . . 13 5.1. IAX2 URI Scheme Registration . . . . . . . . . . . . . . 13 5.2. URI Comparison . . . . . . . . . . . . . . . . . . . . . 15 6. Peer Behavior and Related Messages . . . . . . . . . . . . . 17 6.1. Registration (OPTIONAL) . . . . . . . . . . . . . . . . . 17 6.1.1. Overview . . . . . . . . . . . . . . . . . . . . . . 18 6.1.2. REGREQ Registration Request Message . . . . . . . . . 20 6.1.3. REGAUTH Registration Authentication Response Message . . . . . . . . . . . . . . . . . . . . . . . 21 6.1.4. REGACK Registration Acknowledgment Message . . . . . 21 6.1.5. REGREJ Registration Rejection Message . . . . . . . . 22 6.1.6. REGREL Registration Release Request Message . . . . . 23 6.2. Call Leg Management . . . . . . . . . . . . . . . . . . . 24 6.2.1. Overview . . . . . . . . . . . . . . . . . . . . . . 25 6.2.2. NEW Request Message . . . . . . . . . . . . . . . . . 26 6.2.3. ACCEPT Response Message . . . . . . . . . . . . . . . 28 6.2.4. REJECT Response Message . . . . . . . . . . . . . . . 28 6.2.5. HANGUP Request Message . . . . . . . . . . . . . . . 29 6.2.6. AUTHREP Authentication Reply Message . . . . . . . . 29 6.2.7. AUTHREQ Authentication Request Message . . . . . . . 30 6.3. Call Control . . . . . . . . . . . . . . . . . . . . . . 30 6.3.1. Overview . . . . . . . . . . . . . . . . . . . . . . 30 6.3.2. PROCEEDING Response Message . . . . . . . . . . . . . 31 6.3.3. RINGING Response Message . . . . . . . . . . . . . . 31 6.3.4. ANSWER Response Message . . . . . . . . . . . . . . . 32 6.4. Mid-Call Link Operations . . . . . . . . . . . . . . . . 32 6.4.1. FLASH Request Message . . . . . . . . . . . . . . . . 32 6.4.2. HOLD Request Message . . . . . . . . . . . . . . . . 32 6.4.3. UNHOLD Request Message . . . . . . . . . . . . . . . 32 6.4.4. QUELCH Request Message . . . . . . . . . . . . . . . 33 6.4.5. UNQUELCH Request Message . . . . . . . . . . . . . . 33 6.4.6. TRANSFER Request Message . . . . . . . . . . . . . . 33 6.5. Call Path Optimization . . . . . . . . . . . . . . . . . 34 6.5.1. TXREQ Transfer Request Message . . . . . . . . . . . 36 6.5.2. TXCNT Transfer Connectivity Response Message . . . . 37 6.5.3. TXACC Response Message . . . . . . . . . . . . . . . 37 6.5.4. TXREADY Transfer Ready Response Message . . . . . . . 37 6.5.5. TXREL Transfer Release Response Message . . . . . . . 38 6.5.6. TXMEDIA Transfer Media Message . . . . . . . . . . . 38 6.5.7. TXREJ Transfer Rejection Response Message . . . . . . 39 Spencer, et al. Expires October 17, 2007 [Page 3] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 6.6. Call Tear Down . . . . . . . . . . . . . . . . . . . . . 39 6.7. Network Monitoring . . . . . . . . . . . . . . . . . . . 39 6.7.1. POKE Request Message . . . . . . . . . . . . . . . . 39 6.7.2. PING Request Message . . . . . . . . . . . . . . . . 40 6.7.3. PONG Response Message . . . . . . . . . . . . . . . . 40 6.7.4. LAGRQ Lag Request Message . . . . . . . . . . . . . . 40 6.7.5. LAGRP Lag Response Message . . . . . . . . . . . . . 40 6.8. Digit Dialing . . . . . . . . . . . . . . . . . . . . . . 40 6.8.1. DPREQ Dial Plan Request Message . . . . . . . . . . . 41 6.8.2. DPREP Dial Plan Response Message . . . . . . . . . . 41 6.8.3. DIAL Request Message . . . . . . . . . . . . . . . . 42 6.9. Firmware Download . . . . . . . . . . . . . . . . . . . . 42 6.9.1. FWDOWNL Firmware Download Request Message . . . . . . 43 6.9.2. FWDATA Firmware Data Response Message . . . . . . . . 43 6.10. Provisioning . . . . . . . . . . . . . . . . . . . . . . 44 6.10.1. PROVISION Request Message . . . . . . . . . . . . . . 44 6.11. Miscellaneous . . . . . . . . . . . . . . . . . . . . . . 44 6.11.1. ACK acknowledgement Message . . . . . . . . . . . . . 44 6.11.2. INVAL Invalid Response Message . . . . . . . . . . . 45 6.11.3. VNAK Voice Negative Acknowledgement Message . . . . . 45 6.11.4. MWI Message Waiting Indicator Request Message . . . . 45 6.11.5. UNSUPPORT Unsupported Response Message . . . . . . . 46 6.12. Media Messages . . . . . . . . . . . . . . . . . . . . . 46 6.12.1. DTMF Media Message . . . . . . . . . . . . . . . . . 46 6.12.2. Voice Media Message . . . . . . . . . . . . . . . . . 46 6.12.3. Video Media Message . . . . . . . . . . . . . . . . . 47 6.12.4. Text Media Message . . . . . . . . . . . . . . . . . 47 6.12.5. Image Media Message . . . . . . . . . . . . . . . . . 47 6.12.6. HTML Media Message . . . . . . . . . . . . . . . . . 47 6.12.7. Comfort Noise Media Message . . . . . . . . . . . . 47 7. Message Transport . . . . . . . . . . . . . . . . . . . . . . 48 7.1. Trunking . . . . . . . . . . . . . . . . . . . . . . . . 48 7.2. Timers . . . . . . . . . . . . . . . . . . . . . . . . . 49 7.2.1. Retransmission Timer . . . . . . . . . . . . . . . . 49 7.2.2. Registration Period Timer . . . . . . . . . . . . . . 49 7.3. NAT Considerations . . . . . . . . . . . . . . . . . . . 49 7.4. Encryption . . . . . . . . . . . . . . . . . . . . . . . 50 8. Message Encoding . . . . . . . . . . . . . . . . . . . . . . 51 8.1. Frame Structure . . . . . . . . . . . . . . . . . . . . . 51 8.1.1. Full Frames . . . . . . . . . . . . . . . . . . . . . 51 8.1.2. Mini frames . . . . . . . . . . . . . . . . . . . . . 53 8.1.3. Meta frames . . . . . . . . . . . . . . . . . . . . . 54 8.1.4. Encrypted Frames . . . . . . . . . . . . . . . . . . 59 8.2. Frame Types . . . . . . . . . . . . . . . . . . . . . . . 61 8.2.1. DTMF Frame . . . . . . . . . . . . . . . . . . . . . 61 8.2.2. Voice Frame . . . . . . . . . . . . . . . . . . . . . 61 8.2.3. Video Frame . . . . . . . . . . . . . . . . . . . . . 61 8.2.4. Control Frame . . . . . . . . . . . . . . . . . . . . 61 Spencer, et al. Expires October 17, 2007 [Page 4] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 8.2.5. Null Frame . . . . . . . . . . . . . . . . . . . . . 61 8.2.6. IAX2 Frame . . . . . . . . . . . . . . . . . . . . . 61 8.2.7. Text Frame . . . . . . . . . . . . . . . . . . . . . 62 8.2.8. Image Frame . . . . . . . . . . . . . . . . . . . . . 62 8.2.9. HTML Frame . . . . . . . . . . . . . . . . . . . . . 62 8.2.10. Comfort Noise Frame . . . . . . . . . . . . . . . . . 62 8.2.11. Control Frames . . . . . . . . . . . . . . . . . . . 64 8.2.12. IAX2 Frames . . . . . . . . . . . . . . . . . . . . . 65 8.3. HTML Command Subclasses . . . . . . . . . . . . . . . . . 67 8.4. Information Elements . . . . . . . . . . . . . . . . . . 67 8.4.1. CALLED NUMBER . . . . . . . . . . . . . . . . . . . . 70 8.4.2. CALLING NUMBER . . . . . . . . . . . . . . . . . . . 71 8.4.3. CALLING ANI . . . . . . . . . . . . . . . . . . . . . 71 8.4.4. CALLING NAME . . . . . . . . . . . . . . . . . . . . 72 8.4.5. CALLED CONTEXT . . . . . . . . . . . . . . . . . . . 72 8.4.6. USERNAME . . . . . . . . . . . . . . . . . . . . . . 73 8.4.7. CAPABILITY . . . . . . . . . . . . . . . . . . . . . 73 8.4.8. FORMAT . . . . . . . . . . . . . . . . . . . . . . . 74 8.4.9. LANGUAGE . . . . . . . . . . . . . . . . . . . . . . 74 8.4.10. VERSION . . . . . . . . . . . . . . . . . . . . . . . 74 8.4.11. ADSICPE . . . . . . . . . . . . . . . . . . . . . . . 75 8.4.12. DNID . . . . . . . . . . . . . . . . . . . . . . . . 75 8.4.13. AUTHMETHODS . . . . . . . . . . . . . . . . . . . . . 76 8.4.14. CHALLENGE . . . . . . . . . . . . . . . . . . . . . . 76 8.4.15. MD5 RESULT . . . . . . . . . . . . . . . . . . . . . 77 8.4.16. RSA RESULT . . . . . . . . . . . . . . . . . . . . . 77 8.4.17. APPARENT ADDR . . . . . . . . . . . . . . . . . . . . 78 8.4.18. REFRESH . . . . . . . . . . . . . . . . . . . . . . . 80 8.4.19. DPSTATUS . . . . . . . . . . . . . . . . . . . . . . 80 8.4.20. CALLNO . . . . . . . . . . . . . . . . . . . . . . . 81 8.4.21. CAUSE . . . . . . . . . . . . . . . . . . . . . . . . 81 8.4.22. IAX2 UNKNOWN . . . . . . . . . . . . . . . . . . . . 82 8.4.23. MSGCOUNT . . . . . . . . . . . . . . . . . . . . . . 82 8.4.24. AUTOANSWER . . . . . . . . . . . . . . . . . . . . . 83 8.4.25. MUSICONHOLD . . . . . . . . . . . . . . . . . . . . . 83 8.4.26. TRANSFERID . . . . . . . . . . . . . . . . . . . . . 84 8.4.27. RDNIS . . . . . . . . . . . . . . . . . . . . . . . . 84 8.4.28. PROVISIONING . . . . . . . . . . . . . . . . . . . . 85 8.4.29. AESPROVISIONING . . . . . . . . . . . . . . . . . . . 85 8.4.30. DATETIME . . . . . . . . . . . . . . . . . . . . . . 86 8.4.31. DEVICETYPE . . . . . . . . . . . . . . . . . . . . . 86 8.4.32. SERVICEIDENT . . . . . . . . . . . . . . . . . . . . 87 8.4.33. FIRMWAREVER . . . . . . . . . . . . . . . . . . . . . 87 8.4.34. FWBLOCKDESC . . . . . . . . . . . . . . . . . . . . . 88 8.4.35. FWBLOCKDATA . . . . . . . . . . . . . . . . . . . . . 88 8.4.36. PROVVER . . . . . . . . . . . . . . . . . . . . . . . 89 8.4.37. CALLINGPRES . . . . . . . . . . . . . . . . . . . . . 89 8.4.38. CALLINGTON . . . . . . . . . . . . . . . . . . . . . 90 Spencer, et al. Expires October 17, 2007 [Page 5] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 8.4.39. CALLINGTNS . . . . . . . . . . . . . . . . . . . . . 91 8.4.40. SAMPLINGRATE . . . . . . . . . . . . . . . . . . . . 92 8.4.41. CAUSECODE . . . . . . . . . . . . . . . . . . . . . . 92 8.4.42. ENCRYPTION . . . . . . . . . . . . . . . . . . . . . 95 8.4.43. ENCKEY . . . . . . . . . . . . . . . . . . . . . . . 96 8.4.44. CODEC PREFS . . . . . . . . . . . . . . . . . . . . . 96 8.4.45. RR JITTER . . . . . . . . . . . . . . . . . . . . . . 97 8.4.46. RR LOSS . . . . . . . . . . . . . . . . . . . . . . . 97 8.4.47. RR PKTS . . . . . . . . . . . . . . . . . . . . . . . 98 8.4.48. RR DELAY . . . . . . . . . . . . . . . . . . . . . . 98 8.4.49. RR DROPPED . . . . . . . . . . . . . . . . . . . . . 98 8.4.50. RR OOO . . . . . . . . . . . . . . . . . . . . . . . 99 8.5. Media Formats . . . . . . . . . . . . . . . . . . . . . . 99 9. Example Message Flows . . . . . . . . . . . . . . . . . . . . 101 9.1. Ping/Pong . . . . . . . . . . . . . . . . . . . . . . . . 101 9.2. Lagrq/Lagrp . . . . . . . . . . . . . . . . . . . . . . . 101 9.3. Registration . . . . . . . . . . . . . . . . . . . . . . 102 9.4. Registration . . . . . . . . . . . . . . . . . . . . . . 102 9.5. Provisioning . . . . . . . . . . . . . . . . . . . . . . 103 9.6. Firmware Download . . . . . . . . . . . . . . . . . . . . 103 9.7. Call Path Optimization . . . . . . . . . . . . . . . . . 104 9.8. IAX2 Media Call . . . . . . . . . . . . . . . . . . . . . 104 9.9. IAX2 Media Call via an IAX2 Device . . . . . . . . . . . 106 10. Security Considerations . . . . . . . . . . . . . . . . . . . 108 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 109 12. Implementation Notes . . . . . . . . . . . . . . . . . . . . 110 13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 111 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 112 14.1. Normative References . . . . . . . . . . . . . . . . . . 112 14.2. Informative References . . . . . . . . . . . . . . . . . 112 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 114 Intellectual Property and Copyright Statements . . . . . . . . . 116 Spencer, et al. Expires October 17, 2007 [Page 6] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 1. Introduction Numerous protocols have been specified by the Internet community to support control or signaling of multimedia sessions. In general, these protocols are designed to offer full support for many types of media transmission. This flexible approach adds some overhead to the protocol headers, but allows for the protocol use well beyond the current application. Typically, these protocols reference, but do not specify, the media transmission protocol used to carry the actual stream. This method allows for great flexibility, but again leads to more overhead. Furthermore, multimedia solutions which use different, perhaps dynamic, network addresses for signaling and media transmission frequently suffer from Network Address Translation (NAT) traversal and security challenges. IAX2 is the Inter-Asterisk eXchange protocol which facilitates VoIP connections between servers, and between servers and clients that also use the IAX2 protocol. IAX2 was created through an open source methodology rather than through a traditional standards based methodology. It is an open protocol originally used by Asterisk, a dual licensed open source and commercial PBX server from Digium. Independent IAX2 implementations may be open, proprietary, or licensed in anyway the author seems fit without royalty to the protocol creators. 1.1. Basic Properties IAX2 a very robust and full featured, yet, simple protocol. [wikipedia] It is general enough that it can handle most common types of media streams. However, the protocol is highly optimized for VoIP calls where low overhead and low bandwidth consumption are priorities. This pragmatic aspect makes IAX2 much more efficient for VoIP than protocols which consider possibilities far beyond current needs and specify many more details than are strictly necessary to describe or transport a point-to-point call. Furthermore, because IAX2 is designed to be lightweight and VoIP-friendly, it consumes less bandwidth than more general approaches. IAX2 is a binary protocol, designed to reduce overhead especially in regards to voice streams. Bandwidth efficiency in some places is sacrificed in exchange for bandwidth efficiency for individual voice calls. In addition to efficiency, IAX2's single static UDP port approach makes IAX2 traffic easy for network managers to shape, prioritize, and pass through firewalls. IAX2's basic structure is that it multiplexes signaling and multiple media streams over a single UDP stream between two computers. IAX2 also uses the same UDP port for both its signaling and media messages, and because all communications regarding a call are done over a the same point-to-point path, NAT Spencer, et al. Expires October 17, 2007 [Page 7] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 traversal is much simpler for IAX2 than for other commonly deployed protocols. 1.2. Drawbacks While IAX2 is very effective addressing many of today's communications needs, it does have a few limitations. For instance, IAX2 uses a point-to-point codec negotiation mechanism that limits extensibility because every IAX2 node in a call path must support every used codec to some degree. In addition, the codec definition is controlled by an internally defined 32-bit mask, so the codecs must be defined in the protocol and the maximum number of simultaneous codecs is therefore limited. One of IAX2's design strengths is also presents a potential problem. The use of a single, well-known, port makes the protocol an easier target for denial of service attacks. Real time systems like VoIP are particularly sensitive to these attacks. The protocol is typically deployed with all signaling and media going to a centralized server. While this combined path approach provides a great deal of control, it limits the overall system scalability. IAX2 now provides the ability to split the media from the signaling stream which overcomes this limitation of earlier IAX2 versions. Most IAX2 drawbacks are due to implementation issues rather than protocol issues. Threading presents a series of problems. Many implementations have a limited number of threads available to process IAX2 traffic and can become overwhelmed by high use or denial of service attacks. Newer implementations have additional controls to minimize the impact of these challenges. Spencer, et al. Expires October 17, 2007 [Page 8] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 2. IAX2 Terminology The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. Additionally, this document uses the following terminology: Peer: A host or device that implements the IAX2 protocol. Call: A call is a relationship between two or more parties (i.e., resources such as devices, user agents, or programs) that exists for some time for the purpose of exchanging real-time media. In the context of this document, a call is an end to end relationship where at least the one leg of call path is implemented using the IAX2 protocol. Calling Party: A device or program that initiates a call. Called Party: A device or program to which a call is directed. Context: A context is a named partition of a Dialplan. Dialplan: A Dialplan is a set of rules for associating provided names and numbers with a particular called party. Frame: The atomic communication unit between two IAX2 peers. All IAX2 messages are carried within frames. Information Element (IE): A discrete data unit appended to an IAX2 frame which specifies user or call-specific data. Registrant: A registrant is a peer that makes REGISTER requests in order to advertise the address of a resource, i.e., a device or program to which a call may be directed. Registrar: A registrar is a peer that processes REGISTER requests and places the information it receives in those requests into the location service. [RFC3261]. Spencer, et al. Expires October 17, 2007 [Page 9] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 3. Overview of IAX2 Protocol IAX2 is a peer-to-peer, VoIP-oriented, protocol. IAX2 includes both control and media functions. It can register locations, create, modify, terminate multimedia sessions, and carry the actual media streams specified by the sessions it manages. The protocol is designed and optimized for describing and transporting multimedia calls using Internet Protocol. The basic design approach for IAX2 multiplexes signaling and multiple media streams over a single UDP association between two hosts. This is accomplished by using the same "well-known" UDP port, 4569, for all types of IAX2 traffic. IAX2's unified signaling and media paths achieve NAT transparency, which is an advantage of IAX2 over alternative media transport protocols such as SIP. IAX2 is coded as a binary protocol. One major benefit of using a binary protocol is bandwidth efficiency because the quality of voice calls is frequently related to the amount of bandwidth consumed. This is one way the protocol is specifically optimized to make efficient use of bandwidth for individual voice calls. The bandwidth efficiency for other stream types is sacrificed for the sake of individual voice calls. Other benefits of a binary protocol are robustness against buffer overrun attacks and compact implementation capability, which reduces interoperability issues related to parsing. The atomic communication unit in IAX2 is the "Frame". There are multiple classes of Frames, each of which is described below. In general, "Full Frames" carry signaling/control data, while "Mini Frames" carry media stream data. Full Frames enclose optional 'Information Elements' (IEs). IEs describe various types of user- or call-specific data. "Meta Frames" are used for call trunking or video stream transmission. An IAX2-based call may consist of many call legs, or segments. Each call leg may be implemented using different protocols, e.g., SIP to IAX2 to ISDN (Integrated Services Digital Network). IAX2 is responsible for setting up one or more legs of a complete call path, not necessarily the end-to-end call. IAX2 is an optimized peer-to-peer protocol. If two adjacent call legs utilize the IAX2 protocol and if the intermediate peer determines that it does not need to remain in the call path, it can supervise a calling path change such that it removes itself from the path. This supervision is complete, a call path is not changed until all peers in the optimized call path confirm they can properly communicate. Spencer, et al. Expires October 17, 2007 [Page 10] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 IAX2 supports security features by allowing multiple methods of user authentication and authorization, as well as during peer registration. IAX2 also specifies a generic framework for native encryption. Spencer, et al. Expires October 17, 2007 [Page 11] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 4. Naming Conventions Call Identifier: A call leg is marked with two unique integers, one assigned by each peer involved in creating the call leg. Number: The Calling and Called Numbers are a set of digits and letters identifying a call originator and the desired terminating resource. The term 'Number' is historic and has been expanded to include letters. A peer is responsible for defining its own dialplan. A peer MAY define its dialplan according to ITU-T Recommendation E.164. [E164] However, this is not required. Username: A username is a string used for identification purposes. Spencer, et al. Expires October 17, 2007 [Page 12] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 5. IAX2 Uniform Resource Identifiers 5.1. IAX2 URI Scheme Registration This section registers IAX2 according to the guidelines in [RFC4395]. URI scheme name: iax2. Status: Permanent. URI scheme syntax: The "iax2:" scheme follows the guidelines in [RFC3986]. The general form is as follows: iax2:[username@]host[:port][/number[?context]] where these tokens have the following meanings: iax2: The literal 'iax2:'. username: A string used for identification purposes. host: The domain of the resource. The host part contains either a fully-qualified domain name or numeric IPv4 or IPv6 address. An IPv6 address must be enclosed within brackets (i.e., '[2001:db8::1]') as defined in [RFC3986]. Using the fully-qualified domain name form is RECOMMENDED whenever possible. port: The numeric UDP port number. number: The name or number identifying the resource on that host. context: The name of the host partition in which the service is identified or processed. Spencer, et al. Expires October 17, 2007 [Page 13] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 Examples iax2:example.com/alice iax2:example.com:4569/alice iax2:example.com:4570/alice?friends iax2:192.0.2.4:4569/alice?friends iax2:[2001:db8::1]:4569/alice?friends iax2:example.com/12022561414 iax2:johnQ@example.com/12022561414 ABNF Certain values are included by reference from [RFC3986]: iax2-uri = "iax2:" [userinfo "@" ]host[":" port][ "/" number[ "?" context]] userinfo = host = port = number = *(unreserved | sub-delims | pct-encoded ) context = *(unreserved | sub-delims | pct-encoded ) unreserved = sub-delims = pct-encoded = URI Scheme Semantics: An IAX2 URI identifies a communications resource capable of communicating using the IAX2 Version 2 protocol defined in this document. Within this document, we refer to IAX2 Version 2 protocol URI as IAX2. An IAX2 URI contains enough information to initiate an IAX2-based call with that resource. IAX2 URIs are associated with server resources to which calls may be routed. For instance, an IAX2 URI may represent an appearance on a phone, a voice-mail box on a messaging service, an interactive program, a PSTN address or gateway, or any group of the above. The iax2 uri scheme translates into a location that may be used by the iax2 protocol to establish a new call using the uri scheme components described in the previous section. This new call function is the only defined operation. Spencer, et al. Expires October 17, 2007 [Page 14] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 Encoding considerations: IAX2 URI scheme encoding conforms to the encoding rules established for URIs in [RFC3986]. Applications/protocols that use this URI scheme name: The scheme is used by ENUM Dynamic Delegation Discovery System (DDDS) services to specify resources that support the IAX2 protocol. The IAX2 protocol provides application-layer control and media protocol for creating, modifying, and terminating multimedia sessions over Internet Protocol (IP) networks. Interoperability considerations: None. Security considerations: The IAX2 URI Scheme does not introduce any new security concerns except that it provides a uniform syntax for describing IAX2 resources and that, when published, these addresses are subject to various denial os service attacks. Contact: Ed Guy, edguy@emcsw.com, +1.973.437.4519. Author/Change controller Not Applicable. References: Spencer, M., Shumard, K., Capouch, B., and E. Guy, 'IAX2: Inter- Asterisk eXchange Version 2,' draft-guy-iax-02 Work In Progress, October 2006. 5.2. URI Comparison Some operations in this specification require determining whether two IAX2 URIs are equivalent. IAX2 URIs are compared for equality according to the following rules: All components of the URI MUST be identical except: A host in domain form and in IP address form are considered identical if and only if the host name resolves to exactly one Spencer, et al. Expires October 17, 2007 [Page 15] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 address record and that address record matches the given IP address. The port, if omitted, is considered to be the same as the default, 4569. All URI components, except the username field, are case insensitive, and MUST be normalized to lower case as per section 6.2.2.1 of [RFC3986] before comparison. The URIs within each of the following sets are equivalent: iax2:atlanta.com/alice iax2:AtLaNtA.com/ALicE iax2:atlanta.com:4569/alice iax2:atlanta.com:4569/alice iax2:192.168.1.1/alice (if atlanta.com resolves to 192.168.1.1) The URIs within each of the following sets are not equivalent: iax2:ALICE@atlanta.com/alice iax2:alice@atlanta.com/alice Spencer, et al. Expires October 17, 2007 [Page 16] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 6. Peer Behavior and Related Messages Messages are divided into two categories: reliable and non- guaranteed. The reliable messages are referred to as "Full Frames." In addition to a message type indicator and facilities to ensure reliability, see Section 7, they include the full call identifier. It consists of each of peer's identifiers for the call. Additional attributes, "Information Elements" or "IEs", may be associated with the Full Frame messages. The non-guaranteed messages are referred to as "Mini-Frames" and "Meta Frames" and these more compact messages only have the originating peer's call identifier and may not have any "Information Elements." Peer behavior is presented in several partitions divided by the following functional areas: Registration (OPTIONAL) Call Link Management Call Path Optimization (OPTIONAL) Mid-Call Behavior Call Tear Down Network Monitoring Digit Dialing (OPTIONAL) Firmware Download(OPTIONAL) Provisioning (OPTIONAL) Miscellaneous Media Messages Each of these behavior topics and the messages involved are described in the sections which follow. 6.1. Registration (OPTIONAL) Spencer, et al. Expires October 17, 2007 [Page 17] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 6.1.1. Overview In order for one IAX2 peer to be reachable by another IAX2 peer, the calling peer needs the network address of the receiving peer. This address may be manually provisioned, determined through a shared directory, e.g. an ENUM-like service, [RFC3761] or configured using the IAX2 protocol. IAX2 provides a facility for one peer to register its address and credentials with another so that callers can reach the registrant. The IAX2 registration facility is optional. If implemented, the IAX2 registration protocol MAY be done in parts, e.g., an analog telephone adapter MAY only implement the registrant portion of the protocol. IAX2 allows user authentication via multiple methods. MD5 Message- Digest authentication [RFC1321] uses a md5 sum arrangement, but still requires that both ends have plaintext access to the secret. Rivest, Shamir and Adleman's (RSA) algorithm [RFC2437] allows unidirectional secret knowledge through public/private key pairs. IAX2 Private keys SHOULD always be Triple Data Encryption Standard (3DES) encrypted [RFC1851]. Spencer, et al. Expires October 17, 2007 [Page 18] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 ________________ | | | Unregistered |<--------------------------\ |________________| | | | /Init | | ------------ | | snd REGAUTH | +--------+ | | | | rec REGAUTH | _______V____V___ | ----------- | | | | snd REGREQ | | Reg Sent +----+ | |________________+----------+ | | ^ | rec REGAUTH | rec REGACK | | | /No Credentials| ------------ | | REG timeout | -------------- | snd ack | | ------- | snd ack | | | REGREQ __V___ | _______V____|___ | | | | | | No | | | Registered | | Auth | | |________________| |______| | | ^ | | | rec REGAUTH | | release | /No Credentials| | ------- | -------------- | +-------+ | snd REGREL | snd ack | rec REGAUTH | | | | | ----------- | _V_____V________ | | snd REGREL | | |----------+ | +-----+ Releasing |---------------------------+ |________________| rec ACK ------- x __________ rec REGREJ | | ---------- *->| Rejected | snd ack |__________| Figure 1: Registrant State Diagram Registration, illustrated in Figure 1, is performed by a registrant that sends a username and a registration 'refresh' period to the registrar. This is accomplished with a REGREQ message. If Spencer, et al. Expires October 17, 2007 [Page 19] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 authentication is required, the registrar responds with the REGAUTH message which indicates the types of authentication supported by the registrar. In response, the registrant resends a REGREQ with one of the supported authentications. If the registrant can not authenticate, no further action is necessary. If accepted, the registrar sends a REGACK message which MUST indicate the 'apparent address' and SHOULD indicate the 'refresh'/expire time. If no 'refresh' is sent a default registration expiration of 60 seconds MUST be assumed by both peers. At any time during this exchange, the registrar may send a REGREJ message to indicate a failure. A registration has a specified time period associated with it for which it is valid. This time period begins when the registrar sends a REGACK message. A registrant may extend that time period be repeating the registration process. A registrant MAY also force an expiration in the registrar by sending the REGREL message. This message may be challenged with REGAUTH or if sufficient credentials were included, it will be accepted with REGACK. In response to a REGAUTH, a REGREL message SHOULD be resent using the specified credentials. See sections Section 9.3 and Section 9.4 for example call flows. 6.1.2. REGREQ Registration Request Message The REGREQ occurs independently of any media-carrying call. A REGREQ MUST include the 'username' IE and SHOULD include the 'refresh' IE. A REGREQ is used both for an initial registration request as well as for a reply to a REGAUTH. As a reply to a REGAUTH message, it MUST include credentials such as a response to a REGAUTH's challenge. Upon receipt of a REGREQ message which has credentials, a registrar MUST determine their validity. If valid, it MUST respond with a REGACK message indicating the time period for which this registration is valid. If the provided credentials are not valid or the registrar cannot validate the credentials, the registrar MUST respond with a REGREJ message. If credentials are not provided, the registrar MUST respond with a REGAUTH message that indicates the available authentication methods. Registrants MUST implement this message and registrars MUST be able to process it. Spencer, et al. Expires October 17, 2007 [Page 20] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 The following table specifies IEs for this message: +------------+----------------+-------------+-------------+ | IE | Section | Status | Comments | +------------+----------------+-------------+-------------+ | Username | Section 8.4.6 | Required | | | | | | | | MD5 Result | Section 8.4.15 | Conditional | per REGAUTH | | | | | | | RSA Result | Section 8.4.16 | Conditional | per REGAUTH | | | | | | | Refresh | Section 8.4.18 | Optional | | +------------+----------------+-------------+-------------+ 6.1.3. REGAUTH Registration Authentication Response Message A REGAUTH is a response to a REGREQ or REGREL. It is sent when a registrar requires authentication to permit registration. A REGAUTH message MUST include the 'authentication methods' and 'username' IEs, and the 'MD5 challenge' or 'RSA challenge' IE if the authentication methods include MD5 or RSA. Upon receipt of a REGAUTH message, the registrant MUST resend the REGREQ or REGREL message with one of the requested credentials, if it has the specified credentials. Registrars MUST implement this message and registrants MUST be able to process it. The following table specifies IEs for this message: +--------------+----------------+-------------+---------------+ | IE | Section | Status | Comments | +--------------+----------------+-------------+---------------+ | Username | Section 8.4.6 | Required | | | | | | | | Auth Methods | Section 8.4.13 | Required | | | | | | | | Challenge | Section 8.4.14 | Conditional | If RSA or MD5 | +--------------+----------------+-------------+---------------+ 6.1.4. REGACK Registration Acknowledgment Message A REGACK is sent in response to a REGREQ. A REGACK typically includes the 'refresh' IE specifying the number of seconds before the registration will expire. If the 'refresh' IE is not included with a REGACK, a default registration expiration of 60 seconds MUST be assumed. A REGACK MAY also include the 'username' and 'apparent Spencer, et al. Expires October 17, 2007 [Page 21] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 address' IEs to indicate how the peer identifies the registrant. IEs related to caller identification or the time the registration occurred MAY be sent as well. Receipt of a REGACK message requires an ACK in response. Registrars MUST be able to send this message and registrants MUST be able to process it. The following table specifies IEs for this message: +------------------+----------------+----------+----------+ | IE | Section | Status | Comments | +------------------+----------------+----------+----------+ | Username | Section 8.4.6 | Required | | | | | | | | Date Time | Section 8.4.30 | Required | | | | | | | | Apparent Address | Section 8.4.17 | Required | | | | | | | | Message Count | Section 8.4.23 | Optional | | | | | | | | Calling Number | Section 8.4.2 | Optional | | | | | | | | Calling Name | Section 8.4.4 | Optional | | | | | | | | Firmware Version | Section 8.4.33 | Optional | | | | | | | | Refresh | Section 8.4.18 | Optional | | +------------------+----------------+----------+----------+ 6.1.5. REGREJ Registration Rejection Message A REGREJ indicates that a registration request has been rejected. This rejection can occur for several reasons. A REGREJ MUST include the 'causecode' and 'cause' IEs to specify why registration was rejected. Upon receipt of a REGREJ message, the registrant MUST consider registration process unsuccessful and no further interaction is required. A peer MAY reinitiate the process at later time accounting for potential configuration changes on the registrar or registrant. Both registrants and registrars MUST be capable of sending and processing this message. Spencer, et al. Expires October 17, 2007 [Page 22] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 The following table specifies IEs for this message: +------------+----------------+----------+----------+ | IE | Section | Status | Comments | +------------+----------------+----------+----------+ | Cause | Section 8.4.21 | Required | | | | | | | | Cause Code | Section 8.4.41 | Required | | +------------+----------------+----------+----------+ 6.1.6. REGREL Registration Release Request Message A REGREL is used by a registrant for a forced release of a prior registration. It MUST include the 'username' IE to identify the registrant to be released, and MAY include the 'causecode' and 'cause' IEs to specify why registration is being released. Upon receipt of this message, a peer MUST authenticate the sender using the provided credentials or send a REGAUTH message requesting them. If authenticated it MUST immediately purge its registration of the specified registrant or send a REGREJ message if the registration is not found. Registrants SHOULD be capable of sending this message and registrars MUST be able to process it. The following table specifies IEs for this message: +----------+----------------+-------------+-------------------------+ | IE | Section | Status | Comments | +----------+----------------+-------------+-------------------------+ | Username | Section 8.4.6 | Required | | | | | | | | MD5 | Section 8.4.15 | Conditional | MD5 or RSA Result is | | Result | | | required | | | | | | | RSA | Section 8.4.16 | Conditional | | | Result | | | | | | | | | | Cause | Section 8.4.21 | Optional | | | | | | | | Cause | Section 8.4.41 | Optional | | | Code | | | | +----------+----------------+-------------+-------------------------+ Spencer, et al. Expires October 17, 2007 [Page 23] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 6.2. Call Leg Management +--------+ HANGUP/ack | | _____________|__ | | | | +--------->| Initial |<----+ | |________________|<---------------------+ | | ^ | start call | | | ---------- | | | send NEW | +-------+ | | | | | rec AUTHREQ | | _____V__V__ | ----------- | | | | | snd AUTHREP | +------------| Waiting |----+ | rec REJECT |___________|------------------------>+ ---------- | | ack | rec HANGUP | | --------- | | snd ack | | | rec ACCEPT | | ---------- | +------+ | snd ack | | | PROCEEDING / ack | _________V___V | RINGING / ack | | | | | | Linked |-----+ | |______________|------------------------>+ | rec HANGUP | rec ANSWER | ---------- | ------------ | snd ack | snd ack | | | | | rec HANGUP | _______V________ --------- | | | snd ack | | UP |--------------------->+ |________________|--------------------->+ finish ------ snd HANGUP Figure 2: Call Origination State Diagram Spencer, et al. Expires October 17, 2007 [Page 24] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 +--------+ rec HANGUP/ack | | _____________V__ | rec NEW(no Auth)/snd AUTHREQ | | | | Initial |-----+ rec NEW(not Auth)/snd REJECT | | |________________|<--------------------+ | | rec NEW | | (valid credentials)| | ---------- | +------+ | snd ACCEPT | | | snd PROCEEDING | _________V___V | snd RINGING | | | | | | Linked |-----+ | | | |______________|------------------------>+ | rec HANGUP | /answered | ---------- | ----------- | snd ack | snd ANSWER | | | rec HANGUP | _______V________ --------- | | | snd ack | | UP |--------------------->+ |________________|--------------------->+ finish ------ snd HANGUP Figure 3: Call Termination State Diagram 6.2.1. Overview The IAX2 protocol can be used to setup 'links' or 'call legs' between two peers for the purposes of placing a call. The process, illustrated in Figure 2 and Figure 3, starts when a peer sends a NEW message indicating the destination 'number' (or name) of a Called Party on the remote peer. The remote peer can respond with either a credentials challenge (AUTHREQ), a REJECT message, or an ACCEPT message. The AUTHREQ message indicates the permitted authentication schemes and SHOULD result in the sending of an AUTHREP message with the requested credentials. The REJECT message indicates the call cannot be established at this time. And ACCEPT indicates that the call leg between these two peers is established and that Higher level call signaling (Section 6.3) MAY proceed. After sending or receiving the ACCEPT message, the Call Leg is in the 'Linked' state and is used Spencer, et al. Expires October 17, 2007 [Page 25] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 to pass call control message until the call is completed. Further detail on messages used for this process can be found in Section 6.3. Call Legs are labeled with a pair of identifiers. Each end of the call leg assigns the source or destination identifier during the call leg creation process. 6.2.2. NEW Request Message A NEW message is sent to initiate a call. It is the first call- specific message sent to initiate an actual media exchange between two peers. 'NEW' messages are unique with respect to compared to other Call Supervision messages in that they do not require a destination call identifier in their header. This absence is because the remote peer's source call identifier is not created until after receipt of this frame. Before sending a NEW message, the local IAX2 peer MUST assign a source call identifier that is not currently being used for another call. A time-stamp MUST also be assigned for the call, beginning at zero and incrementing by one each millisecond. Sequence numbers for a NEW message, described in the transport section, (Section 7) are both set to 0. A NEW message MUST include the 'version' IE, and it MUST be the first IE; the order of other IEs is unspecified. A NEW SHOULD generally include IEs to indicate routing on the remote peer, e.g., via the 'called number' IE or to indicate a peer partition or ruleset, the 'called context' IE. Caller identification and CODEC negotiation IEs MAY also be included. Upon receipt of a NEW message, the receiving peer examines the destination and MUST perform one of the following actions: Send a REJECT response, Challenge the caller with an AUTHREQ response, Accept the call using an ACCEPT message, or Abort the connection using a HANGUP message, although the REJECT message is preferred at this point in call. If the call is accepted, the peer MUST progress the call and further respond with one of PROCEEDING, RINGING, BUSY or ANSWER depending on the status of the called party on the peer. See Section 6.3 for further detail. Spencer, et al. Expires October 17, 2007 [Page 26] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 The following table specifies IEs for the NEW message: +--------------+----------------+-------------+---------------------+ | IE | Section | Status | Comments | +--------------+----------------+-------------+---------------------+ | Version | Section 8.4.10 | Required | | | | | | | | Called | Section 8.4.1 | Required | | | Number | | | | | | | | | | Auto Answer | Section 8.4.24 | Optional | | | | | | | | Codecs Prefs | Section 8.4.44 | Required | | | | | | | | Calling | Section 8.4.37 | Required | | | Presentation | | | | | | | | | | Calling | Section 8.4.2 | Optional | | | Number | | | | | | | | | | Calling TON | Section 8.4.38 | Required | | | | | | | | Calling TNS | Section 8.4.39 | Required | | | | | | | | Calling Name | Section 8.4.4 | Optional | | | | | | | | ANI | Section 8.4.3 | Optional | | | | | | | | Language | Section 8.4.9 | Optional | | | | | | | | DNID | Section 8.4.12 | Optional | | | | | | | | Called | Section 8.4.5 | Conditional | 'Default' assumed | | Context | | | if IE excluded | | | | | | | Username | Section 8.4.6 | Optional | | | | | | | | RSA Result | Section 8.4.16 | Conditional | If challenged with | | | | | RSA. | | | | | | | MD5 Result | Section 8.4.15 | Conditional | If challenged with | | | | | MD5 | | | | | | | Format | Section 8.4.8 | Required | | | | | | | | Capability | Section 8.4.7 | Conditional | | | | | | | | ADSICPE | Section 8.4.11 | Optional | | Spencer, et al. Expires October 17, 2007 [Page 27] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 | Date Time | Section 8.4.30 | Optional | Suggested | | | | | | | Encryption | Section 8.4.42 | Optional | | +--------------+----------------+-------------+---------------------+ 6.2.3. ACCEPT Response Message An ACCEPT response is issued when a NEW message is received, and authentication has taken place (if required). It acknowledges receipt of a NEW message and indicates that the call leg has been setup on the terminating side, including assigning a CODEC. An ACCEPT message MUST include the 'format' IE to indicate its desired CODEC to the originating peer. The CODEC format MUST be one of the formats sent in the associated NEW command. Upon receipt of an ACCEPT, an ACK MUST be sent and the CODEC for the call MAY be configured using the 'format' IE from the received ACCEPT. The call then waits for an ANSWER, HANGUP or other call control signal. (See Section 6.3.) If a subsequent ACCEPT message is received for a call which has already started, or has not sent a NEW message, the message MUST be ignored. The following table specifies IEs for this message: +--------+---------------+----------+----------+ | IE | Section | Status | Comments | +--------+---------------+----------+----------+ | Format | Section 8.4.8 | Required | | +--------+---------------+----------+----------+ 6.2.4. REJECT Response Message A REJECT response is sent to indicate that a NEW, AUTHREP, DIAL, or ACCEPT request has been denied. It MAY be due to an authentication failure, an invalid username or if a peer cannot provide a valid password or response to an issued challenge. It MAY also be used to notify a peer of a call setup failure, e.g., when IAX2 peers cannot negotiate a CODEC to use or when a firmware download request cannot be satisfied. Upon receipt of a REJECT message, the call leg is destroyed and no further action is required. (Note: REJECT messages require an explicit ACK.) REJECT messages MAY include the 'causecode' and 'cause' IEs to indicate the rejection reason. Spencer, et al. Expires October 17, 2007 [Page 28] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 The following table specifies IEs for this message: +------------+----------------+----------+----------+ | IE | Section | Status | Comments | +------------+----------------+----------+----------+ | Cause | Section 8.4.21 | Optional | | | | | | | | Cause Code | Section 8.4.41 | Optional | | +------------+----------------+----------+----------+ 6.2.5. HANGUP Request Message A HANGUP message is sent by either peer and indicates a call tear- down. It MAY include the 'causecode' and 'cause' IEs to indicate the reason for terminating the call. Upon receipt of a HANGUP message, an IAX2 peer MUST immediately respond with an ACK, and then destroy the call leg at its end. After a HANGUP message has been received for a call leg, any messages received which reference that call leg (i.e., have the same source/destination call identifiers) MUST be answered with an INVAL message. This indicates that the received message is invalid because the call no longer exists. After sending a HANGUP message, the sender MUST destroy the call and respond to subsequent messages regarding this call with an INVAL message. The following table specifies IEs for this message: +------------+----------------+----------+----------+ | IE | Section | Status | Comments | +------------+----------------+----------+----------+ | Cause | Section 8.4.21 | Optional | | | | | | | | Cause Code | Section 8.4.41 | Optional | | +------------+----------------+----------+----------+ 6.2.6. AUTHREP Authentication Reply Message An AUTHREP MUST include the appropriate challenge response or password IE, and is only sent in response to an AUTHREQ. An AUTHREP requires a response of either an ACCEPT or a REJECT. Typical reasons for rejecting an AUTHREP include 'destination does not exist' and 'suitable bearer not found'. Spencer, et al. Expires October 17, 2007 [Page 29] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 The following table specifies IEs for this message: +------------+----------------+-------------+----------+ | IE | Section | Status | Comments | +------------+----------------+-------------+----------+ | RSA Result | Section 8.4.16 | Conditional | If RSA | | | | | | | MD5 Result | Section 8.4.15 | Conditional | If MD5 | +------------+----------------+-------------+----------+ 6.2.7. AUTHREQ Authentication Request Message The AUTHREQ message is sent in response to a NEW message if authentication is required for the call to be accepted. It MUST include the 'authentication methods' and 'username' IEs, and the 'challenge' IE if MD5 or RSA authentication is specified. Upon receiving an AUTHREQ message, the receiver MUST respond with an AUTHREP or HANGUP message. The following table specifies IEs for this message: +--------------+----------------+----------+----------+ | IE | Section | Status | Comments | +--------------+----------------+----------+----------+ | Username | Section 8.4.6 | Required | | | | | | | | Auth Methods | Section 8.4.13 | Required | | | | | | | | Challenge | Section 8.4.14 | Required | | +--------------+----------------+----------+----------+ 6.3. Call Control 6.3.1. Overview IAX2's call control messages provide end-to-end signaling functions common to other telephony control protocols. The messages include RINGING, ANSWER, BUSY, and PROCEEDING. These messages MUST only be sent after an IAX2 call leg has been ACCEPTed. In response to an exchange starting with a NEW message, typically, the first call control message is RINGING, however, a PROCEEDING message MAY precede it or the call MAY proceed directly to the ANSWER message. If the call is answered, an ANSWER message will be sent. Other possibilities include a "BUSY" indication, or if the called party's service cannot be reached, the call will be town down using the link-level HANGUP and an appropriate cause code. Spencer, et al. Expires October 17, 2007 [Page 30] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 If the link was started with a DIAL message, the sequence is an optional PROCEEDING, then optional RINGING, then ANSWER or BUSY. Of course, a link level HANGUP MAY occur at any time. Various extensions to IAX2 Control messages have been deployed for passing application-specific data over IAX2 control link. One such extensions is an application that controls ham radio transceivers. An IAX2 peer that receives a control message that is not understood MUST respond with the UNSUPPORT message. The mandatory IAX2 control messages are explained below. 6.3.2. PROCEEDING Response Message The PROCEEDING message SHOULD be sent to a calling party when their call request is being processed by a further network element but has not yet reached the called party. Upon receipt of a PROCEEDING message, the peer SHOULD perform protocol-specific actions to indicate this fact to the calling party, e.g., tones, an ISUP Proceeding message, etc. If the prior call leg is utilizing the IAX2 protocol, a PROCEEDING message MUST be sent to that peer. The processing of this message at an originating or transcoding peer is not specified, however, if possible, the status may be displayed to the calling party. The PROCEEDING message does not require any IEs. 6.3.3. RINGING Response Message This message is sent from a terminating party to indicate that that the called party's service has processed the call request and is being alerted to the call. A IAX2 RINGING message MUST be sent to an IAX2-based calling party when the peer determines that the called party is being alerted, e.g., when their phone is ringing. Upon receipt of an IAX2 RINGING message, the peer MUST pass this indication to the calling party, unless the calling party has already received such indication. For an initiating peer, this is typically done by starting the ring-back tone, however, many implementations start ringback before ringing in order to meet user expectations. If the calling party is using the IAX2 protocol, a RINGING message MUST be passed to this caller. The RINGING message does not require any IEs. Spencer, et al. Expires October 17, 2007 [Page 31] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 6.3.4. ANSWER Response Message This message is sent from the called party to indicate that party has accepted the call request and is communicating with the calling party. Upon receipt of this message, any ring-back or other progress tones MUST be terminated and the communications channel MUST be opened. The ANSWER message does not require any IEs. 6.4. Mid-Call Link Operations 6.4.1. FLASH Request Message The FLASH message is sent to indicate a mid call feature. Its interpretation is system dependent and if it is not expected, it SHOULD be ignored. Typically, this message is only sent from Analog Telephone adapters when a brief circuit interruption is made during an answered call. The FLASH message does not require any IEs. 6.4.2. HOLD Request Message The HOLD message is sent to cause the remote system to stop transmitting audio on this channel, and optionally replace the audio with music or other sounds. If the remote system cannot perform this request, it SHOULD be ignored. The HOLD message SHOULD only be sent in IAX2 calls which are started using the DIAL message. The HOLD message does not require any IEs. 6.4.3. UNHOLD Request Message The UNHOLD message is sent to cause the remote system to resume transmitting audio on this channel. If the remote system cannot perform this request, it SHOULD be ignored. The UNHOLD message SHOULD only be sent in IAX2 calls after the HOLD message. The UNHOLD message does not require any IEs. Spencer, et al. Expires October 17, 2007 [Page 32] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 6.4.4. QUELCH Request Message The QUELCH message is sent to cause the remote peer to squelch or stop transmitting audio on this channel. It MAY replace the audio sent to the further party with music or other sounds. If the remote system cannot perform this request, it SHOULD be ignored. The QUELCH message MUST only be sent in IAX2 calls after an ACCEPT is sent or received; it SHOULD only be used on calls which are started using the NEW message. The QUELCH message does not require any IEs. 6.4.5. UNQUELCH Request Message The UNQUELCH message is sent to cause the remote system to resume transmitting audio on this channel. If it previously replaced the audio with music or other sounds, it MUST discontinue it immediately. If the remote system cannot perform this request, it SHOULD be ignored. The UNQUELCH message SHOULD only be sent in IAX2 calls after the QUELCH message. The UNQUELCH message does not require any IEs. 6.4.6. TRANSFER Request Message The TRANSFER message causes the receiving peer to restart the call using another specified number. The receiving peer MUST be on the calling side of this call leg and the new call behavior is unspecified. After processing this message, a HANGUP message SHOULD be sent and the call leg torn down. When sending a TRANSFER message, the new number to which the call is being transferred MUST be included in the CALLED_NUMBER IE and a CALLED_CONTEXT IE MAY be included. The call leg MUST not be used for anything else and MAY be torn down. The following table specifies IEs for this message: +-----------+---------------+----------+----------------------------+ | IE | Section | Status | Comments | +-----------+---------------+----------+----------------------------+ | Called | Section 8.4.1 | Required | | | Number | | | | | | | | | Spencer, et al. Expires October 17, 2007 [Page 33] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 | Called | Section 8.4.5 | Optional | Use this IE if context is | | Context | | | other than default. | +-----------+---------------+----------+----------------------------+ 6.5. Call Path Optimization If a peer is handling a call between two other IAX2 peers and the peer no longer has any need to monitor the progress, content, or duration of the call, it MAY remove itself from the call by directing the other two peers to communicate directly. This call path optimization, or "supervised transfer," is done in a manner that ensures the call will not be lost in the process; the initiating peer does not give up control of the process until it has confirmed the other two peers are communicating. Note: the parties involved in the call are not aware of this operation; it is purely a network operation. Spencer, et al. Expires October 17, 2007 [Page 34] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 ________________ rec TXREJ | | rec TXREL ---------- *--------->| None |<-----------------+ snd TXREJ |________________| ack ^ to other | | | | V | | | | * (From All) | /Init Transfer | | rec TXREQ | ------------ | | --------- | snd TXREQ | | snd TXCNT | to both | | | _v___________v__ | | | | | Begin |----------------->+ |________________| | | | | rec TXACC | | rec TXREADY | --------- | | --------- | snd TXREADY | | x | | | | _v___________v__ | | |----------------->+ ----------| Ready |---------- | | |________________| | | | | | | /Both Legs Ready| /Both Legs Ready| rec TXMEDIA| | and not media-only| and media-only | | | ------------ | ------------ | -----------| | snd TXREL | snd TXMEDIA | x | | | | | | ____V____ _____V___ ___V_____ | | | | | | | | | Release | | Media | | Media | | |_________| |_________| | Pass | | | |_________| | | | | V V | rec TXCNT +------------------------->+ ---------- (In any state) snd TXACC Figure 4: Call Path Optimization State Diagram When a peer initiates this procedure, both call legs MUST be in the Spencer, et al. Expires October 17, 2007 [Page 35] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 UP state, i.e., they MUST have sent or received the ACCEPT message for that call leg. To start, it sends a TXREQ message with the addresses and information from the other remote peers to each its neighbors. If capable of performing this procedure, they begin transmitting all channel information to both the initiating peer and the new remote peer. They also send a TXCNT message indicating packet counts for the call leg to the new remote peer. Each TXCNT message is acknowledged with a TXACC message. The peers respond by sending a TXREADY message to the initiator indicating that they have confirmed the new communications path. When all remote peers have sent the initiator a TXREADY message, the transfer is successful and the initiator responds with a TXREL and has finished its involvement with the call. If during the transfer process, the two remote peers cannot communicate, they send a TXREJ message to the initiator. An example is shown in Section 9.7. These messages are described in the sections which follow: 6.5.1. TXREQ Transfer Request Message The TXREQ message is sent by a peer to initiate the transfer process. When sent, It MUST be sent to both adjacent peers involved in the call. It MUST include the following Information Elements: +------------------+----------------+----------+----------+ | IE | Section | Status | Comments | +------------------+----------------+----------+----------+ | Apparent Address | Section 8.4.17 | Required | | | | | | | | Call Number | Section 8.4.20 | Required | | | | | | | | Transfer ID | Section 8.4.26 | Required | | +------------------+----------------+----------+----------+ The Apparent Address is the IP address data structure address for the other remote peer. The Call Number IE is The callid used by the other remote peer and the Transfer ID is a unique number assigned by the initiator. Upon receipt of a TXREQ message for a valid call from the corresponding remote peer, a peer MUST respond by attempting to communicate with the newly specified remote peer. This task is accomplished by sending a TXCNT message directly to the peer at the address specified in the Apparent Address parameter. Spencer, et al. Expires October 17, 2007 [Page 36] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 6.5.2. TXCNT Transfer Connectivity Response Message The TXCNT message is used to verify connectivity with a potential replacement peer for a call. It MUST include the TRANSFERID IE. Upon receipt on a message of this type, and if the peer has previously received a TXREQ for this call leg, the peer MUST respond with a TXACC message. If the TXCNT Message is not successfully transmitted or if a TXACC message is not received in response to it, the transfer process MUST be aborted by sending a TXREJ message to the initiating host. It MUST include the following Information Element: +----------+----------------+----------+----------------------------+ | IE | Section | Status | Comments | +----------+----------------+----------+----------------------------+ | Transfer | Section 8.4.26 | Required | A unique number assigned | | ID | | | by the initiator. | +----------+----------------+----------+----------------------------+ 6.5.3. TXACC Response Message Like the TXCNT message, the TXACC message is used to verify connectivity with a potential replacement peer. It MUST include the TRANSFERID IE. Upon receipt on a message of this type if the peer is attempting to transfer this call leg, the peer stops sending call related media to the initiating peer and sends a TXREADY message to it. It MUST include the following Information Element: +----------+----------------+----------+----------------------------+ | IE | Section | Status | Comments | +----------+----------------+----------+----------------------------+ | Transfer | Section 8.4.26 | Required | A unique number assigned | | ID | | | by the initiator. | +----------+----------------+----------+----------------------------+ 6.5.4. TXREADY Transfer Ready Response Message The TXREADY message indicates that the sending peer has verified connectivity with the peer which it was instructed to transfer the call. It MUST include the TRANSFERID IE. When TXREADY messages are received from both remote peers, it MUST discontinue media transport and send a TXREL message to each peer. Spencer, et al. Expires October 17, 2007 [Page 37] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 It MUST include the following Information Element: +----------+----------------+----------+----------------------------+ | IE | Section | Status | Comments | +----------+----------------+----------+----------------------------+ | Transfer | Section 8.4.26 | Required | A unique number assigned | | ID | | | by the initiator. | +----------+----------------+----------+----------------------------+ 6.5.5. TXREL Transfer Release Response Message The TXREL message indicates that the transfer process has successfully completed. After sending and upon receipt of this message, no further interaction (other than an ACK, of course) is needed between the peers on this call-leg. The TXREL is also used to revert a split-media call (one where the media and signaling follow different paths) to a call where the media and signaling follow the same path. It MUST include the following Information Element: +-------------+----------------+----------+----------+ | IE | Section | Status | Comments | +-------------+----------------+----------+----------+ | Call Number | Section 8.4.20 | Required | | +-------------+----------------+----------+----------+ 6.5.6. TXMEDIA Transfer Media Message The TXREL message indicates that the MEDIA transfer process has successfully completed. After sending and upon processing of this message, full frames MUST continue to follow the original signaling path and media frames MUST follow the newly negotiated path. This split-path process continues until the call ends with a HANGUP or peer receives a TXREL message for the call leg. A peer MAY force the paths to rejoin by sending a TXREL message. It MUST include the following Information Element: +-------------+----------------+----------+----------+ | IE | Section | Status | Comments | +-------------+----------------+----------+----------+ | Call Number | Section 8.4.20 | Required | | +-------------+----------------+----------+----------+ Spencer, et al. Expires October 17, 2007 [Page 38] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 6.5.7. TXREJ Transfer Rejection Response Message The TXREJ MAY be sent at anytime during the transfer process to indicate that the transfer cannot proceed. Upon receiving a TXREJ message, if the receiver is the initiating peer, it MUST form a TXREJ message and send it to the other remote peer. The TXREJ message does not require any IEs. 6.6. Call Tear Down The messages used to finish a call vary depending on the particular process the call is in at the time. The terminal messages for a call are: HANGUP. See Section 6.2.5. REJECT. See Section 6.2.4. TRANSFER. See Section 6.4.6. TXREADY. See Section 6.5.4. These messages are discussed in their respective sections. Also, if the reliable transport procedures determines that messaging cannot be maintained, the call leg MUST be torn down without any other indications over the errant IAX2 call leg. 6.7. Network Monitoring The IAX2 protocol has various tools to determine the network load. It uses the POKE message to monitor reachability of remote peer and the LAGRQ message to measure the quality of a current call leg including the jitter buffer delay. 6.7.1. POKE Request Message A POKE message is sent to test connectivity of a remote IAX2 peer. It is similar to a PING message, except that it MUST be sent when there is no existing call to the remote endpoint. It MAY also be used to "qualify" a user to a remote peer, so that the remote peer can maintain awareness of the state of the user. A POKE MUST have 0 as its destination call number. Upon receiving a POKE message, the peer MUST respond with a PONG message. This message does not require any IEs. Spencer, et al. Expires October 17, 2007 [Page 39] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 6.7.2. PING Request Message A PING message is sent to test connectivity of the remote IAX2 endpoint on an existing call. Transmission of a PING MAY occur when a peer-defined number of seconds have passed without receiving an incoming media frame on a call, or by default every 20 seconds. Receipt of a PING requires an acknowledging PONG be sent. This message does not require any IEs. 6.7.3. PONG Response Message A PONG message is a response to a PING or a POKE. It acknowledges the connection. The receiver uses the time-stamp of the received PING or POKE and its times to determine the Round Trip Time of the connection. Several receiver report IEs MAY be included with a PONG, including received jitter, received frames, delay, and dropped frames. Receipt of a PONG requires an ACK. This message does not require any IEs. 6.7.4. LAGRQ Lag Request Message A LAGRQ is a lag request. It is sent to determine the lag between two IAX2 endpoints, including the amount of time used to process a frame through a jitterbuffer (if any). It requires a clock-based time-stamp, and MUST be answered with a LAGRP, which MUST echo the LAGRQ's time-stamp. The lag between the two peers can be computed on the peer sending the LAGRQ by comparing the time-stamp of the LAGRQ and the time the LAGRP was received. This message does not require any IEs. 6.7.5. LAGRP Lag Response Message A LAGRP is a lag reply, sent in response to a LAGRQ message. It MUST send the same time-stamp it received in the LAGRQ after passing the received frame through any jitter buffer the peer has configured. This message does not require any IEs. 6.8. Digit Dialing Digit Dialing support is an optional portion of the IAX2 protocol designed to support devices that do not maintain their own dial plans, for instance, analog telephone adapters, or ATAs. The dialing portion of the IAX2 protocol MAY be implemented for the client/ phone-side, server side or not all. The exchanges work as a series Spencer, et al. Expires October 17, 2007 [Page 40] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 of Dialing Plan requests (DPREQ) each followed by a response (DPREP) indicating if additional digits SHOULD be collected before sending the call. The sections that follow describe these messages and the rules associated with them. 6.8.1. DPREQ Dial Plan Request Message A DPREQ is a request for the server to analyze the passed called number and determine if there is a valid dialing pattern on the remote peer. It MUST include the 'called number' IE to specify what extension is being queried. This command is used in the case where a local peer does not handle its own dialplan/extension switching. The local peer can inquire (as a user dials) how the remote peer perceives the 'called number'. If a DPREP is received indicating that the number is valid, a DIAL MAY be sent. This message MAY be sent by the client and MUST be implemented on servers which provide IAX2 dialing support. It MUST include the following Information Element: +-------------+----------------+----------+----------+ | IE | Section | Status | Comments | +-------------+----------------+----------+----------+ | Call Number | Section 8.4.20 | Required | | +-------------+----------------+----------+----------+ 6.8.2. DPREP Dial Plan Response Message A DPREP is a reply to a DPREQ, containing the status of the dialplan entry requested in the 'called number' IE of the DPREQ. It MUST include the 'called number', 'dpstatus', and 'refresh' IEs. The called number is the same one received in the 'called number' IE of the DPREQ. The 'dpstatus' IE contains the status of the dialplan entry referenced by the received called number. The status indicates whether the called number exists, can exist, needs more digits, or is invalid. More information can be found in Section 8.4 under the DPSTATUS information element. The 'refresh' IE specifies the number of minutes the 'dpstatus' is valid. If the 'refresh' IE is not present, a default 10 minutes period is assumed. The sending of this message MUST be implemented by servers which support IAX2 dialing. Clients which support IAX2 dialing MUST be capable of receiving such messages. Spencer, et al. Expires October 17, 2007 [Page 41] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 It MUST include the following Information Elements: +----------+----------------+----------+----------------------------+ | IE | Section | Status | Comments | +----------+----------------+----------+----------------------------+ | Call | Section 8.4.20 | Required | | | Number | | | | | | | | | | Dial | Section 8.4.20 | Required | Indicates if number | | Plan | | | exists, is a partial | | Status | | | match, etc. | | | | | | | Dial | Section 8.4.20 | Optional | Inclusion is strongly | | Plan | | | suggested. The default is | | Refresh | | | 10 minutes. | +----------+----------------+----------+----------------------------+ 6.8.3. DIAL Request Message The DIAL message is used with IAX2 peers that do not maintain their own dialplan/extension routing. Once an extension is validated by one or more DPREQ/DPREP exchanges, the number MAY be dialed in a DIAL message, using the 'called number' IE to specify the extension it is attempting to reach. The remote peer then handles the remaining aspects of call setup, including ringing the extension and notifying the local peer when it has been answered following the same requirements as the NEW command (Section 6.2.2). The following table specifies the IEs used by this message: +-----------+---------------+----------+----------------------------+ | IE | Section | Status | Comments | +-----------+---------------+----------+----------------------------+ | Called | Section 8.4.1 | Required | | | Number | | | | | | | | | | Called | Section 8.4.5 | Optional | Use this IE if context is | | Context | | | other than default. | +-----------+---------------+----------+----------------------------+ 6.9. Firmware Download The IAX2 protocol can download firmware to devices which request it. This is an optional portion of the protocol designed such that an embedded device can retrieve binary images from a 'server' peer. Note Well: There is no security on firmware downloads. Spencer, et al. Expires October 17, 2007 [Page 42] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 6.9.1. FWDOWNL Firmware Download Request Message An FWDOWNL message is a request made by an IAX2 device to download a firmware binary using the IAX2 protocol. The FWDOWNL message MUST include the device type and the block IEs. If the recipient is capable of transmitting a firmware image, it does so with a FWDATA message which includes the 'fwblockdesc' (Section 8.4.34 and 'fwblockdata' (Section 8.4.35) IEs. On receiving this message, the server MUST determine if it has the firmware for the specified device and respond with a FWDATA message containing the data block of firmware that was requested. If the firmware is not available or the offset is invalid, it MUST respond with a REJECT message. (See Section 6.2.4.) The following table specifies IEs used by this message +-------------+----------------+----------+----------+ | IE | Section | Status | Comments | +-------------+----------------+----------+----------+ | DEVTYPE | Section 8.4.31 | Required | | | | | | | | FWBLOCKDATA | Section 8.4.35 | Required | | +-------------+----------------+----------+----------+ 6.9.2. FWDATA Firmware Data Response Message An FWDATA message is sent in response to an FWDOWNL message. It carries a block of a firmware and IEs that identify which block is being carried. The 'fwblockdata' and 'fwblockdesc' IEs are used. If the FWDATA is the last of the transaction (that is, 'fwblockdata' is of length 0), an ACK is required upon receipt. Otherwise, an FWDOWNL requesting the next block to download in the 'fwblockdesc' IE is required. The ordered set of firmware blocks is concatenated to make up the downloaded firmware. The following table specifies IEs used by this message +-------------+----------------+----------+-------------------------+ | IE | Section | Status | Comments | +-------------+----------------+----------+-------------------------+ | FWBLOCKDESC | Section 8.4.34 | Required | | | | | | | | FWBLOCKDATA | Section 8.4.35 | Required | Length 0 at end of | | | | | transfer. | +-------------+----------------+----------+-------------------------+ Spencer, et al. Expires October 17, 2007 [Page 43] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 6.10. Provisioning The IAX2 protocol allows provisioning of peer devices. This is a useful way to specify configuration information to a device that does not maintain state. Provisioning generally allows for configuration of network information (e.g., server address, UDP port number to use, type of service setting, etc.), user information (e.g., username, password, etc.), and CODEC information (i.e., which CODECs the device MAY use when transmitting media to an IAX2 peer). Provisioning can be configured for a particular class or type of device using the 'device type' information element, or for one specific device using the 'service identifier' information element. 6.10.1. PROVISION Request Message A PROVISION message is sent by a provisioning peer to a remote IAX2 device. It includes either the 'provisioning' or the 'AES provisioning' IE, which contains the data to be used to perform the actual provisioning of the device. The format is device specific. The following table specifies IEs used by this message +-----------------+----------------+-------------+------------------+ | IE | Section | Status | Comments | +-----------------+----------------+-------------+------------------+ | PROVISIONING | Section 8.4.28 | Conditional | Either | | | | | PROVISIOINNG or | | | | | AESPROVISIONING | | | | | MUST be | | | | | included. | | | | | | | AESPROVISIONING | Section 8.4.29 | Conditional | | +-----------------+----------------+-------------+------------------+ 6.11. Miscellaneous 6.11.1. ACK acknowledgement Message An ACK acknowledges the receipt of an IAX2 message. An ACK is sent upon receipt of a full frame which does not have any other protocol- defined response. An ACK MUST have both a source call number and destination call number. It MUST also not change the sequence number counters, and MUST return the same time-stamp it received. This time-stamp allows the originating peer to determine to which message the ACK is responding. Receipt of an ACK requires no action. An ACK MAY also be sent as an initial acknowledgment of an IAX2 message which requires some other protocol-defined message Spencer, et al. Expires October 17, 2007 [Page 44] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 acknowledgment, as long as the required message is also sent within some peer-defined amount of time. This allows the acknowledging peer to delay transmission of the proper IAX2 message, which may add security against brute-force password attacks during authentication exchanges. When the following messages are received, an ACK MUST be sent in return: NEW, HANGUP, REJECT, ACCEPT, PONG, AUTHREP, REGREL, REGACK, REGREJ, TXREL. ACKs SHOULD not be expected by any peer and their purpose is purely to force the transport layer to be up to date. The ACK message does not requires any IEs. 6.11.2. INVAL Invalid Response Message An INVAL is sent as a response to a received message that is not valid. This occurs when an IAX2 peer sends a message on a call after the remote peer has hungup its end. Upon receipt of an INVAL, a peer MUST destroy its side of a call. The INVAL message does not requires any IEs. 6.11.3. VNAK Voice Negative Acknowledgement Message A VNAK is sent when a message is received out of order, particularly when a mini frame is received before the first full voice frame on a call. It is a request for retransmission of dropped messages. A message is considered out of sequence if the received iseqno is different than the expected iseqno. On receipt of a VNAK, a peer MUST retransmit all frames with a higher sequence number than the VNAK message's iseqno. The VNAK message does not requires any IEs. 6.11.4. MWI Message Waiting Indicator Request Message An MWI message is used to indicate to a remote peer that it has one or more messages waiting. It MAY include the 'msgcount' IE to specify how many messages are waiting. The following table specifies IEs used by this message +----------+----------------+----------+------------+ | IE | Section | Status | Comments | +----------+----------------+----------+------------+ | MSGCOUNT | Section 8.4.23 | Optional | Suggested. | +----------+----------------+----------+------------+ Spencer, et al. Expires October 17, 2007 [Page 45] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 6.11.5. UNSUPPORT Unsupported Response Message An UNSUPPORT message is sent in response to a message that is not supported by an IAX2 peer. This occurs when an IAX2 command with an unrecognized or unsupported subclass is received. No action is required upon receipt of this message, though the peer SHOULD be aware that the message referred to in the optionally included 'IAX2 unknown' IE is not supported by the remote peer. The following table specifies IEs used by this message +---------+----------------+----------+------------+ | IE | Section | Status | Comments | +---------+----------------+----------+------------+ | UNKNOWN | Section 8.4.22 | Optional | Suggested. | +---------+----------------+----------+------------+ 6.12. Media Messages The IAX2 protocol supports many types of media and these are transported through the same UDP port as the other messages. Voice and video are unique in that they utilize two different encodings which use two different procedures to support. Abbreviated 'Mini frames' are normally used for audio and video, however, each time the time-stamp is a multiple of 32,768 (0x8000 hex) a standard or 'Full Frame' MAY be sent. This approach facilitates efficiency and reliability by sending compressed messages without guaranteed delivery packets most of the time and periodically having reliable exchanges with the peer which invokes call tear down procedures if communication is no longer successful. Upon receiving any media message, except the abbreviated audio and video mini frames, an ACK message MUST be sent. The content SHOULD be passed to the application or further to the next call leg. The data MAY be buffered before it is presented to the user. 6.12.1. DTMF Media Message The message carries a single digit of DTMF (Dual Tone Multiple Frequency). Useful background information about DTMF can be found in [RFC2833], but, note that IAX2 does not use the RTP protocol. 6.12.2. Voice Media Message The message carries voice data and indicates the CODEC used. Spencer, et al. Expires October 17, 2007 [Page 46] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 6.12.3. Video Media Message The frame carries video data and indicates the video format of the data. 6.12.4. Text Media Message The frame carries a text message. 6.12.5. Image Media Message This message carries a single image. The image MUST fit in one message in this version of the protocol. 6.12.6. HTML Media Message The HTML message class carries HTML and related data as well as status about the display of that HTML page. The subclass parameter indicates the HTML content type. It MAY be a URL, the start, middle or end of a data block. If a peer receives an HTML message for a channel that does not support HTML, it MUST respond with an HTML message that has the HTML NOT SUPPORTED indication. When a devices that supports HTML completes loading the page, it SHOULD send a LOAD COMPLETE message 6.12.7. Comfort Noise Media Message This message indicates that comfort noise SHOULD be played. It has a parameter that indicates the level. The noise is to be locally generated. Spencer, et al. Expires October 17, 2007 [Page 47] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 7. Message Transport IAX2 is sent over UDP and uses an application level protocol to provide reliable transport where needed. With respect to transport, there are two messages formats: reliable or 'Full Frames' and unacknowledged 'Mini' or 'Meta' frames. All messages except certain voice and video messages are reliable. Reliable messages are transported by a scheme which maintains message counts and time stamps for both peers involved in the call. The counts are per call. Each peer maintains a timer for all reliable messages and MUST periodically retransmit those messages until they acknowledge or the retry limit is exceeded. When starting a call, the outgoing and incoming messages sequence numbers MUST both be set to zero. Each reliable message that is sent increments the message count by one except the ACK, INVAL, TXCNT, TXACC, and VNAK messages which do not change the message count. The message includes the outgoing message count and the highest numbered incoming message which has been received. In addition, it contains a time-stamp which represents the number of milliseconds since the call started. Or, in the case of certain network timing messages, it contains a copy of the time-stamp sent to it. Timestamps MAY be approximate, but, MUST be in order. When any message is received, the timestamps in MUST be checked to make sure that they are in order. If a message is received out of order, it MUST be ignored and a VNAK message sent to resynchronize the peers. And if the message is a reliable message, the incoming message counter MUST be used to acknowledge all the messages up to that sequence number which have been sent. If no acknowledgment is received after a locally configured number of retries, default 4, the call leg SHOULD be considered unusable and the call MUST be torn down without any further interaction on this call leg. 7.1. Trunking IAX2 allows multiple media exchanges between the same two peers to be multiplexed into a single trunk call coalescing media payload into a combined packet. This decreases bandwidth usage as there are fewer total packets being transmitted. Trunking MAY occur in one or both directions of an IAX2 exchange. A trunk consists of a trunk header and one or more trunked IAX2 calls. The trunk message contains a time-stamp specifying the time of transmission of the trunk frame. The audio data from the trunked calls are encapsulated in the trunk frame following the header. Each trunked call consists of two octets Spencer, et al. Expires October 17, 2007 [Page 48] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 specifying the call's source number, two octets specifying the length in octets of the media data, and the media data itself. IAX2 permits transmitting the timestamps of each encapsulated mini frame as well, so that accurate timing information can be used for jitter buffers, etc. A flag in the meta command header specifies whether the encapsulated mini frames retain their original timestamps. If they do not retain them, they MUST assume the time-stamp in the trunk header upon being received by the trunk peer. 7.2. Timers There are various timers in the IAX2 protocol. There are other application level timers such as the call timers and ring timer which are beyond the scope of this document. This section describes the IAX2 timers and specifies their default values and behavior. 7.2.1. Retransmission Timer The message retransmission procedures are described in section Section 7. On each call, there is a timer for how long to wait for an acknowledgment of a message. This timer starts at twice the measured round trip time from the last PING/PONG command. If a retransmission is needed, it is exponentially increased until it meets a boundary value. The maximum retry time period boundary is 10 seconds. 7.2.2. Registration Period Timer Registrations are valid for a specified time period. It is the client's responsibility to renew this registration before the time period expires. The registrations SHOULD be renewed at random intervals to prevent network congestion. A registrar MUST monitor this time period and invalidate the registration if the client/ registrant has not renewed their registration before the timer elapses. 7.3. NAT Considerations IAX2 is very well suited to operating behind NAT due to its single port approach. This approach eliminates any start of call media stream delays while the NAT gateway establishes a bidirectional port association. Deploying a single IAX2 server behind a NAT gateway requires little effort. If the server acts as a registrar, the IAX2 UDP port on the NAT gateway must be forwarded to the server. If the server acts as a registrant, the default, 60 second, REGREQ refresh timer should be sufficient to maintain a port association in the NAT gateway, however, a static port mapping is preferred. Spencer, et al. Expires October 17, 2007 [Page 49] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 If multiple servers are to be deployed behind a single NAT gateway, most NAT gateways require each IAX2 server to use different UDP ports. Of course, there may be NAT implementations which recognize when multiple devices utilize the same private port and and manage it appropriately. 7.4. Encryption IAX2 supports call encryption using the symmetric key, Rijndael [AES] block cipher (also called AES---Advanced Encryption Standard). Rijndael is a 128-bit block cipher utilizing a shared secret. IAX2 encrypts on a call-by-call basis starting with a plain-text NEW message indicating, in addition to the other message parameters, that the call should be encrypted. This indication is given by sending the ENCRYPTION IE Section 8.4.42 in the NEW request message. If the called host supports encryption, it will respond with a plain-text AUTHREQ message which also includes the ENCRYPTION IE. All subsequent messages in the call MUST be encrypted. If the called host does not support encryption, the AUTHREQ sent in response to the NEW must not include the ENCRYPTION IE and the calling host MUST either HANGUP the request or continue with the unencrypted call. The key to use in encrypting the messages is computed by taking the the CHALLENGE IE Section 8.4.14 from the AUTHREQ and concatenating any one of the shared passwords then computing the 128-bit MD5 digest of this combination. To decrypt, if there is more than password for the peer, each must be tried until the message is successfully decoded. The key remains constant for the duration of the call. Only the data portion of the messages are encoded. Spencer, et al. Expires October 17, 2007 [Page 50] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 8. Message Encoding 8.1. Frame Structure This section contains the specification for each type of frame that IAX2 defines. 8.1.1. Full Frames Full frames can send signaling or media data. Generally full frames are used to control initiation, setup, and termination of an IAX2 call, but they can also be used to carry stream data (though this is generally not optimal). Full frames are sent reliably, so all full frames require an immediate acknowledgment upon receipt. This acknowledgment can be explicit via an 'ACK' message (see Section 8.2.12) or implicit based upon receipt of an appropriate response to the full frame issued. The standard full frame header length is 12 octets. Field descriptions: 'F' bit This bit specifies whether the frame is a full frame or not. If the 'F' bit is set to 1 the frame is a full frame. If it is set to 0 it is not a full frame. Source call number This 15-bit value specifies the call number the transmitting client uses to identify this call. The source call number for an active call MUST not be in use by another call on the same client. Call numbers MAY be reused once a call is no longer active, i.e. when either there is positive acknowledgment that the call has been destroyed or when all possible timeouts for the call have expired. 'R' bit This bit specifies whether the frame is being retransmitted or not. If the 'R' bit is set to 0 the frame is being transmitted for the first time. If it is set to 1 the frame is being retransmitted. IAX2 does not specify a retransmit timeout; this is left to the implementor. Destination call number Spencer, et al. Expires October 17, 2007 [Page 51] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 This 15-bit value specifies the call number the transmitting client uses to reference the call at the remote peer. This number is the same as the remote peer's source call number. The destination call number uniquely identifies a call on the remote peer. The source call number uniquely identifies the call on the local peer. time-stamp The time-stamp field contains a 32-bit time-stamp maintained by an IAX2 peer for a given call. The time-stamp is an incrementally increasing representation of the number of milliseconds since the first transmission of the call. OSeqno The 8-bit OSeqno field is the outbound stream sequence number. Upon initialization of a call its value is 0. It increases incrementally as full frames are sent. When the counter overflows, it silently resets to 0. ISeqno The 8-bit ISeqno field is the inbound stream sequence number. Upon initialization of a call its value is 0. It increases incrementally as full frames are received. At any time the ISeqno of a call represents the next expected inbound stream sequence number. When the counter overflows, it silently resets to 0. Frametype The Frametype field identifies the type of message carried by the frame. See Section 8.2 for more information. 'C' bit This bit determines how the remaining 7 bits of the Subclass field are coded. If the 'C' bit is set to 1, the Subclass value is interpreted as a power of 2. If it is not set, the Subclass value is interpreted as a simple seven bit unsigned integer. Spencer, et al. Expires October 17, 2007 [Page 52] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |F| Source Call Number |R| Destination Call Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | time-stamp | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OSeqno | ISeqno | Frame Type |C| Subclass | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : Data : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 5: Full Frame Binary Format 8.1.2. Mini frames Mini Frames are so named because their header is a minimal 4 octets. Mini frames carry no control or signaling data; their sole purpose is to carry a media stream on an already-established IAX2 call. They are sent unreliably. This decision was made because VoIP calls typically can miss several frames without significant degradation in call quality while the incurred overhead in ensuring reliability increases bandwidth requirements and decreases throughput. Further, because voice calls are typically sent in real time, lost frames are too old to be reintegrated into the audio stream by the time they can be retransmitted. Field descriptions: 'F' bit Mini frames MUST have the 'F' bit set to 0 to specify that they are not full frames. Source call number The source call number is the number that is used by the transmitting peer to identify the current call. time-stamp Mini frames carry a 16-bit time-stamp, which is the lower 16 bits of the transmitting peer's full 32-bit time-stamp for the call. The time-stamp allows synchronization of incoming frames so that they MAY be processed in chronological order instead of the (possibly different) order in which they are received. The 16-bit Spencer, et al. Expires October 17, 2007 [Page 53] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 time-stamp wraps after 65.536 seconds, at which point a full frame SHOULD be sent to notify the remote peer that its time-stamp has been reset. A call MUST continue to send mini frames starting with time-stamp 0 even if acknowledgment of the resynchronization is not received. The F bit, source call number, and 16-bit time-stamp comprise the entire four octet header for a full frame. Following this header is the actual stream data, of arbitrary length up to the maximum supported by the network. Mini frames are implicitly defined to be of type 'voice frame' (frametype 2; see Section 8.2). The subclass is implicitly defined by the most recent full voice frame of a call (i.e. the subclass for a voice frame specifies the CODEC used with the stream). The first voice frame of a call SHOULD be sent using the CODEC agreed upon in the initial CODEC negotiation. On-the-fly CODEC negotiation is permitted by sending a full voice frame specifying the new CODEC to use in the subclass field. 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |F| Source call number | time-stamp | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : Data : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 6: Mini Frame Binary Format 8.1.3. Meta frames Meta frames serve one of two purposes. Meta video frames allow the transmission of video streams with an optimized header. They are similar in purpose to mini voice frames. Meta trunk frames are used for trunking multiple IAX2 media streams between two peers into one header, to further minimize bandwidth consumption. 8.1.3.1. Meta Video Frames Field descriptions: 'F' bit Spencer, et al. Expires October 17, 2007 [Page 54] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 Meta video frames MUST have the 'F' bit set to 0 to indicate that they are not full frames. Meta Indicator The meta indicator is a 15-bit field of all zeroes, used to indicate that the frame is a meta frame. Meta frames are identifiable because the first 16 bits will always be zero in any meta frame, whereas full or mini frames will have either the 'F' bit set or some (nonzero) value for the source call number (or both). 'V' bit The 'V' bit in a meta video frame is set to 1 to specify that the frame is a meta video frame. Source call number The call number that is used by the transmitting peer to identify this video call. time-stamp Meta video frames carry a 16-bit time-stamp, which is the lower 16 bits of the transmitting peer's full 32-bit time-stamp for the call. When this time-stamp wraps, a full frame SHOULD be sent to notify the remote peer that the time-stamp has been reset to 0. Following the time-stamp is the actual video stream data. Meta video frames are implicitly defined to be of type 'video frame' (frametype 3; see Section 8.2). The video CODEC used is implicitly defined by the subclass of the most recent full video frame of a call. 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |F| Meta Indicator |V| Source Call Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |?| time-stamp | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | Data | : : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Spencer, et al. Expires October 17, 2007 [Page 55] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 Figure 7: Meta Video Frame Binary Format 8.1.3.2. Meta Trunk Frames IAX2 natively supports two methods of trunking multiple media streams between two peers into a single association. The first method sends a standard meta header, along with a single 32-bit time-stamp describing the transmission time of the trunk frame. Following the time-stamp are one or more media frames consisting of the call number and the length in octets of the stream data included in the frame. The second method of trunking is very similar to the first. It sends a standard meta header, including the 32-bit time-stamp describing the time of transmission of the trunk frame. But the media frames included in the trunk are actually complete mini frames, including the 16-bit time-stamp for each call. The first method uses slightly less bandwidth (2 fewer octets per call in the trunk), while the second method maintains the individual timestamps for each call so that jitterbuffering can use the actual timestamps associated with a call instead of the (less accurate) time-stamp representing the entire trunk. Either method is permissible for trunking. Field descriptions: 'F' bit Meta trunk frames MUST have the 'F' bit set to 0 to indicate that they are not full frames. Meta Indicator The meta indicator is a 15-bit field of all zeroes, used to indicate that the frame is a meta frame. Meta frames are identifiable because the first 16 bits will always be zero in any meta frame, whereas full or mini frames will have either the 'F' bit set or some (nonzero) value for the source call number (or both). 'V' bit The 'V' bit in a meta trunk frame is set to 0 to specify that the frame is not a meta video frame. Meta Command This seven bit field identifies whether the meta frame is a trunk or not. A value of '1' indicates that the frame is a meta trunk frame. All other values are reserved for future use. Spencer, et al. Expires October 17, 2007 [Page 56] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 Command Data This 8-bit field specifies flags for options which apply to a trunked call. The least significant bit of the field is the 'trunk timestamps' flag. A value of 0 indicates that the calls in the trunk do not include their individual timestamps. A value of 1 indicates that the calls do each include their own time-stamp. All other bits are reserved for future use. time-stamp Meta trunk frames carry a 32-bit time-stamp, which represents the actual time of transmission of the trunk frame. This is distinct from the timestamps of the calls included in the trunk. Following the 32-bit time-stamp is one or more trunked calls. If the 'trunk timestamps' flag is set to 0, each entry consists of 2 octets specifying the source call number of the call, 2 octets specifying the length in octets of the media data, and then the media data. If the 'trunk timestamps' flag is set to 1, each entry consists of 2 octets specifying the length in octets of the media data, and then a mini frame (2 octets specifying source call number, 2 octets specifying 16-bit time-stamp, and the media data). The following 2 diagrams help illustrate this pictorially. Spencer, et al. Expires October 17, 2007 [Page 57] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |F| Meta Indicator |V|Meta Command | Cmd Data (0) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | time-stamp | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |R| Source Call Number | Data Length (in octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : Data : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |R| Source Call Number | Data Length (in octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : Data : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 8: Meta Trunk Frame Binary Format (trunk timestamps 0) Spencer, et al. Expires October 17, 2007 [Page 58] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |F| Meta Indicator |V|Meta Command | Cmd Data (1) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | time-stamp | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Data Length (in octets) |R| Source Call Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | time-stamp | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | Data | : : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Data Length (in octets) |R| Source Call Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | time-stamp | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | Data | : : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 9: Meta Trunk Frame Binary Format (trunk timestamps 1) 8.1.4. Encrypted Frames All of the above frames may be encrypted. The header call numbers are passed through in the clear, first 4 bytes for a full frame or 2 bytes for a mini frame. The remainder of the frame is padded with between 16 and 32 bytes of random data, then encrypted with AES each block being xor'd with the previous block. The padding is added at the front of the data. Figure Figure 10 shows a padded full frame before encryption. and Figure Figure 11 shows the frame after encryption. Other frame types follws the same procedure, except the clear text portion is shorter as described above. Spencer, et al. Expires October 17, 2007 [Page 59] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |F| Source Call Number |R| Destination Call Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 12 Random bytes | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 28 Random bits |padding| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : between 0 and 15 (as indicated by the padding field above) : : Random bytes : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : Remainder of Actual Frame : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 10: Full Frame before encryption Since AES requires a 16 byte block size, some padding is essential. This padding has been placed at the beginning of the payload because it makes it more difficult to take advantage of the predictability of the IAX frame header. For example, the first encrypted Frame an IAX2 client sends within an incoming IAX call is entirely predictable: It is always an ACK - where even the timestamp is guessable as it is the time the AUTHREP packet was sent. 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |F| Source Call Number |R| Destination Call Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Encrypted data | | Multiple of 16 bytes | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 11: Frame after encryption The same rules apply to the miniframes, except that the initial unencrypted portion is only 2 bytes. Spencer, et al. Expires October 17, 2007 [Page 60] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 8.2. Frame Types The IAX2 protocol specifies 10 types of possible frames for the "frametype" field of a full frame. They are: 8.2.1. DTMF Frame The frame carries a single digit of DTMF (Dual Tone Multiple Frequency). More information about DTMF can be found in RFC 2833[RFC2833]. For DTMF frames, the subclass is the actual DTMF digit carried by the frame. 8.2.2. Voice Frame The frame carries voice data. The subclass specifies the audio format of the data. Predefined voice formats can be found in Section 8.5 below. 8.2.3. Video Frame The frame carries video data. The subclass specifies the video format of the data. Predefined video formats can be found in Section 8.5 below. 8.2.4. Control Frame The frame carries session control data, i.e. it refers to control of a device connected to an IAX2 endpoint. The subclass is a value from Section 8.2.11 describing the device control signal. 8.2.5. Null Frame Frames with the Null value MUST not be transmitted. 8.2.6. IAX2 Frame The frame carries control data that provides IAX2 protocol specific endpoint management. This frametype is used to manage IAX2 protocol interactions that are generally independent of the type of endpoints. The subclass is a value from Section 8.2.12 describing an IAX2 event. Spencer, et al. Expires October 17, 2007 [Page 61] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 8.2.7. Text Frame The frame carries a non-control text message. All text frames have a subclass of 0. 8.2.8. Image Frame The frame carries a single image. The subclass describes the format of the image from Section 8.5 below. 8.2.9. HTML Frame The frame carries HTML data. The subclass is a value from the HTML Subclasses table in Section 8.3. 8.2.10. Comfort Noise Frame The frame carries comfort noise. The subclass is the level of comfort noise in -dBov. Spencer, et al. Expires October 17, 2007 [Page 62] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 The following table specifies all valid Frame Type Values: +------+-------------+--------------------------+-------------------+ | TYPE | Description | Subclass Description | Data Description | +------+-------------+--------------------------+-------------------+ | 0x01 | DTMF | 0-9, A-D, *, # | Undefined | | | | | | | 0x02 | Voice | Audio Compression Format | Data | | | | | | | 0x03 | Video | Video Compression Format | Data | | | | | | | 0x04 | Control | See Control Frame Types | Varies with | | | | | subclass | | | | | | | 0x05 | Null | Undefined | Undefined | | | | | | | 0x06 | IAX2 | See IAX2 Protocol | Information | | | Control | Messages | Elements | | | | | | | 0x07 | Text | Always 0 | Raw Text | | | | | | | 0x08 | Image | Image Compression Format | Raw image | | | | | | | 0x09 | HTML | See HTML Frame Types | Message Specific | | | | | | | 0x0A | Comfort | Level in -dBov of | None | | | Noise | comfort noise | | +------+-------------+--------------------------+-------------------+ Spencer, et al. Expires October 17, 2007 [Page 63] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 8.2.11. Control Frames The following table specifies all valid Control Frame Subclasses: +-------------+---------------+-------------------------------------+ | VALUE | Name | Description | +-------------+---------------+-------------------------------------+ | 0x01 | Hangup | The call has been hungup at the | | | | remote end. | | | | | | 0x02 | Reserved | Reserved for future use | | | | | | 0x03 | Ringing | Remote end is ringing (ringback) | | | | | | 0x04 | Answer | Remote end has answered | | | | | | 0x05 | Busy | Remote end is busy | | | | | | 0x06 | Reserved | Reserved for future use | | | | | | 0x07 | Reserved | Reserved for future use | | | | | | 0x08 | Congestion | The call is congested. | | | | | | 0x09 | Flash Hook | Flash hook | | | | | | 0x0a | Reserved | Reserved for future use | | | | | | 0x0b | Option | Device-specific options are being | | | | transmitted | | | | | | 0x0c | Key Radio | Key Radio | | | | | | 0x0d | Unkey Radio | Unkey Radio | | | | | | 0x0e | Call Progress | Call is in progress | | | | | | 0x0f | Call | Call is proceeding | | | Proceeding | | | | | | | 0x10 | Hold | Call is placed on hold | | | | | | 0x11 | Unhold | Call is taken off hold | +-------------+---------------+-------------------------------------+ Spencer, et al. Expires October 17, 2007 [Page 64] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 8.2.12. IAX2 Frames Frames of type 'IAX2' are used to provide management of IAX2 endpoints. They handle IAX2 signaling (e.g. call setup, maintenance, and teardown). They MAY also handle direct transmission of media data, but this is not optimal for VoIP calls. They do not carry session-specific control (e.g. device state), as this is the purpose of Control Frames. The IAX2 commands are listed and described below. The following table specifies all valid IAX2 Frame Values: +------+-----------+-----------------------------------------+ | Hex | Name | Description | +------+-----------+-----------------------------------------+ | 0x01 | NEW | Initiate a new call | | | | | | 0x02 | PING | Ping request | | | | | | 0x03 | PONG | Ping or poke reply | | | | | | 0x04 | ACK | Explicit acknowledgment | | | | | | 0x05 | HANGUP | Initiate call teardown | | | | | | 0x06 | REJECT | Reject a call | | | | | | 0x07 | ACCEPT | Accept a call | | | | | | 0x08 | AUTHREQ | Authentication request | | | | | | 0x09 | AUTHREP | Authentication reply | | | | | | 0x0a | INVAL | Invalid message | | | | | | 0x0b | LAGRQ | Lag request | | | | | | 0x0c | LAGRP | Lag reply | | | | | | 0x0d | REGREQ | Registration request | | | | | | 0x0e | REGAUTH | Registration authentication | | | | | | 0x0f | REGACK | Registration acknowledgement | | | | | | 0x10 | REGREJ | Registration reject | | | | | | 0x11 | REGREL | Registration release | | | | | Spencer, et al. Expires October 17, 2007 [Page 65] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 | 0x12 | VNAK | Video/Voice retransmit request | | | | | | 0x13 | DPREQ | Dialplan request | | | | | | 0x14 | DPREP | Dialplan reply | | | | | | 0x15 | DIAL | Dial | | | | | | 0x16 | TXREQ | Transfer request | | | | | | 0x17 | TXCNT | Transfer connect | | | | | | 0x18 | TXACC | Transfer accept | | | | | | 0x19 | TXREADY | Transfer ready | | | | | | 0x1a | TXREL | Transfer release | | | | | | 0x1b | TXREJ | Transfer reject | | | | | | 0x1c | QUELCH | Halt audio/video [media] transmission | | | | | | 0x1d | UNQUELCH | Resume audio/video [media] transmission | | | | | | 0x1e | POKE | Poke request | | | | | | 0x1f | Reserved | Reserved for future use | | | | | | 0x20 | MWI | Message waiting indication | | | | | | 0x21 | UNSUPPORT | Unsupported message | | | | | | 0x22 | TRANSFER | Remote transfer request | | | | | | 0x23 | PROVISION | Provision an IAX2 device | | | | | | 0x24 | FWDOWNL | Download firmware request | | | | | | 0x25 | FWDATA | Transmit firmware data | +------+-----------+-----------------------------------------+ Spencer, et al. Expires October 17, 2007 [Page 66] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 8.3. HTML Command Subclasses IAX2 HTML Command Subclasses: +--------+----------------------------+ | NUMBER | DESCRIPTION | +--------+----------------------------+ | 1 | Sending a URL | | | | | 2 | Data frame | | | | | 4 | Beginning frame | | | | | 8 | End frame | | | | | 16 | Load is complete | | | | | 17 | Peer does not support HTML | | | | | 18 | Link URL | | | | | 19 | Unlink URL | | | | | 20 | Reject Link URL | +--------+----------------------------+ 8.4. Information Elements IAX2 messages sent as full frames MAY carry information elements to specify user- or call-specific data. Information elements are appended to a frame header in its data field. Zero, one, or multiple information elements MAY be included with any IAX2 message. Information elements are coded as follows: The first octet of any information element consists of the "IE" field. The IE field is an identification number which defines the particular information element. Table 31 lists the defined information elements and each information element is defined below the table. The second octet of any information element is the "data length" field. It specifies the length in octets of the information element's data field. The remaining octet(s) of an information element contain the actual data being transmitted. The representation of the data is dependent on the particular information element as identified by Spencer, et al. Expires October 17, 2007 [Page 67] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 its "IE" field. Some information elements carry binary data, some carry UTF-8 [RFC3629] data, and some have no data field at all. The data representation for each information element is described below. The following table specifies the Information Element Binary Format: 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IE | Data Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : DATA : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Following is a table of the information elements IAX2 defines, and a brief description of each information element's purpose. More information about each IE may be found below the table. +------+-----------------+------------------------------------------+ | HEX | NAME | DESCRIPTION | +------+-----------------+------------------------------------------+ | HEX | NAME | DESCRIPTION | | | | | | 0x01 | CALLED NUMBER | Number/extension being called | | | | | | 0x02 | CALLING NUMBER | Calling number | | | | | | 0x03 | CALLING ANI | Calling number ANI for billing | | | | | | 0x04 | CALLING NAME | Name of caller | | | | | | 0x05 | CALLED CONTEXT | Context for number | | | | | | 0x06 | USERNAME | Username (peer or user) for | | | | authentication | | | | | | 0x07 | PASSWORD | Password for authentication | | | | | | 0x08 | CAPABILITY | Actual CODEC capability | | | | | | 0x09 | FORMAT | Desired CODEC format | | | | | Spencer, et al. Expires October 17, 2007 [Page 68] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 | 0x0a | LANGUAGE | Desired language | | | | | | 0x0b | VERSION | Protocol version | | | | | | 0x0c | ADSICPE | CPE ADSI capability | | | | | | 0x0d | DNID | Originally dialed DNID | | | | | | 0x0e | AUTHMETHODS | Authentication method(s) | | | | | | 0x0f | CHALLENGE | Challenge data for MD5/RSA | | | | | | 0x10 | MD5 RESULT | MD5 challenge result | | | | | | 0x11 | RSA RESULT | RSA challenge result | | | | | | 0x12 | APPARENT ADDR | Apparent address of peer | | | | | | 0x13 | REFRESH | When to refresh registration | | | | | | 0x14 | DPSTATUS | Dialplan status | | | | | | 0x15 | CALLNO | Call number of peer | | | | | | 0x16 | CAUSE | Cause | | | | | | 0x17 | IAX2 UNKNOWN | Unknown IAX2 command | | | | | | 0x18 | MSGCOUNT | How many messages waiting | | | | | | 0x19 | AUTOANSWER | Request auto-answering | | | | | | 0x1a | MUSICONHOLD | Request musiconhold with QUELCH | | | | | | 0x1b | TRANSFERID | Transfer Request Identifier | | | | | | 0x1c | RDNIS | Referring DNIS | | | | | | 0x1d | PROVISIONING | Provisioning info | | | | | | 0x1e | AESPROVISIONING | AES Provisioning info | | | | | | 0x1f | DATETIME | Date/Time | | | | | | 0x20 | DEVICETYPE | Device Type | | | | | | 0x21 | SERVICEIDENT | Service Identifier | | | | | Spencer, et al. Expires October 17, 2007 [Page 69] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 | 0x22 | FIRMWAREVER | Firmware revision | | | | | | 0x23 | FWBLOCKDESC | Firmware block description | | | | | | 0x24 | FWBLOCKDATA | Firmware block of data | | | | | | 0x25 | PROVVER | Provisioning Version | | | | | | 0x26 | CALLINGPRES | Calling presentation | | | | | | 0x27 | CALLINGTON | Calling type of number | | | | | | 0x28 | CALLINGTNS | Calling transit network select | | | | | | 0x29 | SAMPLINGRATE | Supported sampling rates | | | | | | 0x2a | CAUSECODE | Hangup cause | | | | | | 0x2b | ENCRYPTION | Encryption format | | | | | | 0x2c | ENCKEY | 128-bit AES encryption key | | | | | | 0x2d | CODEC PREFS | CODEC Negotiation | | | | | | 0x2e | RR JITTER | Received jitter, as in rfc1889 | | | | | | 0x2f | RR LOSS | Received loss, as in rfc1889 | | | | | | 0x30 | RR PKTS | Received frames | | | | | | 0x31 | RR DELAY | Max playout delay for received frames in | | | | ms | | | | | | 0x32 | RR DROPPED | Dropped frames (presumably by | | | | jitterbuffer) | | | | | | 0x33 | RR OOO | Frames received Out of Order | +------+-----------------+------------------------------------------+ Table 31: Information Element Definitions 8.4.1. CALLED NUMBER The purpose of the CALLED NUMBER information element is to indicate the number or extension being called. It carries UTF-8-encoded data. The CALLED NUMBER information element MUST use UTF-8 encoding and not numeric data because it is not limited to E.164 numbers ([E164]), national numbers, or even numbers. It is possible for a number or Spencer, et al. Expires October 17, 2007 [Page 70] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 extension to include non-numeric characters. A CALLED NUMBER MAY be a SIP URI [RFC3261] The CALLED NUMBER information element is generally sent with IAX2 NEW, DPREQ, DPREP, DIAL, and TRANSFER messages. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x01 | Data Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : UTF-8-encoded CALLED NUMBER : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.2. CALLING NUMBER The purpose of the CALLING NUMBER information element is to indicate the number or extension of the calling entity to the remote peer. It carries UTF-8-encoded data. The CALLING NUMBER information element is usually sent with IAX2 NEW messages. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x02 | Data Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : UTF-8-encoded CALLING NUMBER : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.3. CALLING ANI The purpose of the CALLING ANI information element is to indicate the calling number ANI (Automatic number identification) for billing. It carries UTF-8-encoded data. The CALLING ANI information element MAY be sent with an IAX2 NEW message, but it is not required. Spencer, et al. Expires October 17, 2007 [Page 71] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x03 | Data Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : UTF-8-encoded CALLING ANI : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.4. CALLING NAME The purpose of the CALLING NAME information element is to indicate the calling name of the transmitting peer. It carries UTF-8-encoded data. The CALLING NAME information element is usually sent with IAX2 NEW messages. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x04 | Data Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : UTF-8-encoded CALLING NAME : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.5. CALLED CONTEXT The purpose of the CALLED CONTEXT information element is to indicate the context in the remote peer's dialplan the call is trying to reach. It carries UTF-8-encoded data. The CALLED CONTEXT information element MAY be sent with IAX2 NEW or TRANSFER messages, though it is not required. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x05 | Data Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : UTF-8-encoded CALLED CONTEXT : | | Spencer, et al. Expires October 17, 2007 [Page 72] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.6. USERNAME The purpose of the USERNAME information element is to specify the identity of the user participating in an IAX2 message exchange. It carries UTF-8-encoded data. The USERNAME information element MAY be sent with IAX2 NEW, AUTHREQ, REGREQ, REGAUTH, or REGACK messages, or any time a peer needs to identify a user. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x06 | Data Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : UTF-8-encoded USERNAME : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.7. CAPABILITY The purpose of the CAPABILITY information element is to indicate the media CODEC capabilities of an IAX2 peer. Its data is represented in a four octet bitmask according to Section 8.5. Multiple CODECs MAY be specified by logically OR'ing them into the CAPABILITY information element. The CAPABILITY information element is sent with IAX2 NEW messages if appropriate for the CODEC negotiation method the peer is using. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x08 | 0x04 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | CAPABILITY according to Media | | Format Subclass Values Table | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Spencer, et al. Expires October 17, 2007 [Page 73] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 8.4.8. FORMAT The purpose of the FORMAT information element is to indicate a single preferred media CODEC. When sent with a NEW message, the indicated CODEC is the desired CODEC an IAX2 peer wishes to use for a call. When sent with an ACCEPT message, it indicates the actual CODEC that has been selected for the call. Its data is represented in a four octet bitmask according to Section 8.5. Only one CODEC MUST be specified in the FORMAT information element. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x09 | 0x04 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | FORMAT according to Media | | Format Subclass Values Table | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.9. LANGUAGE The purpose of the LANGUAGE information element is to indicate the language in which the transmitting peer would like the remote peer to send signaling information. It carries UTF-8-encoded data. The LANGUAGE information element MAY be sent with an IAX2 NEW message. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x0a | Data Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : UTF-8-encoded LANGUAGE : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.10. VERSION The purpose of the VERSION information element is to indicate the protocol version the peer is using. Peers at each end of a call MUST use the same protocol version. Currently the only supported version is 2. The data field of the VERSION information element is 2 octets long. Spencer, et al. Expires October 17, 2007 [Page 74] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 The VERSION information element MUST be sent with an IAX2 NEW message. When Sent, the VERSION information element MUST be the first IE in the message. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x0b | 0x02 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x0002 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.11. ADSICPE The purpose of the ADSICPE information element is to indicate the CPE ADSI capability. The data field of the ADSICPE information element is 2 octets long. The ADSICPE information element MAY be sent with an IAX2 NEW message. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x0c | 0x02 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ADSICPE Capability | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.12. DNID The purpose of the DNID information element is to indicate the Dialed Number ID, which may differ from the 'called number'. It carries UTF-8-encoded data. The DNID information element MAY be sent with an IAX2 NEW message. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x0d | Data Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : UTF-8-encoded DNID Data : Spencer, et al. Expires October 17, 2007 [Page 75] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.13. AUTHMETHODS The purpose of the AUTHMETHODS information element is to indicate the authentication methods a peer accepts. It is sent as a bitmask 2 octets long. The table below lists the valid authentication methods. The AUTHMETHODS information element MUST be sent with IAX2 AUTHREQ and REGAUTH messages. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x0e | 0x02 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Valid Authentication Methods | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The following table lists valid values for authentication: +--------+--------------------------+ | METHOD | DESCRIPTION | +--------+--------------------------+ | 0x0001 | Reserved (was Plaintext) | | | | | 0x0002 | MD5 | | | | | 0x0004 | RSA | +--------+--------------------------+ 8.4.14. CHALLENGE The purpose of the CHALLENGE information element is to offer the MD5 or RSA challenge to be used for authentication. It carries the actual UTF-8-encoded challenge data. The CHALLENGE information element MUST be sent with IAX2 AUTHREQ and REGAUTH messages. Spencer, et al. Expires October 17, 2007 [Page 76] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x0f | Data Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : UTF-8-encoded Challenge Data : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.15. MD5 RESULT The purpose of the MD5 RESULT information element is to offer an MD5 response to an authentication CHALLENGE. It carries the actual UTF- 8-encoded challenge result. The MD5 RESULT information element MAY be sent with IAX2 AUTHREP and REGREQ messages if an AUTHREQ or REGAUTH and appropriate CHALLENGE has been received. This information element MUST NOT be sent except in response to a CHALLENGE. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x10 | Data Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : UTF-8-encoded MD5 Result : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.16. RSA RESULT The purpose of the RSA RESULT information element is to offer an RSA response to an authentication CHALLENGE. It carries the actual UTF- 8-encoded challenge result. The RSA RESULT information element MAY be sent with IAX2 AUTHREP and REGREQ messages if an AUTHREQ or REGAUTH and appropriate CHALLENGE have been received. This information element MUST NOT be sent except in response to a CHALLENGE. Spencer, et al. Expires October 17, 2007 [Page 77] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x11 | Data Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : UTF-8-encoded RSA Result : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.17. APPARENT ADDR The purpose of the APPARENT ADDR information element is to indicate the perceived network connection information used to reach a peer, which may differ from the actual address when the peer is behind NAT. The APPARENT ADDR IE is populated using the source address values of the UDP and IP headers in the IAX2 message to which this response is generated. The data field of the APPARENT ADDR information element is the same as the POSIX sockaddr struct for the address family in use (i.e., sockaddr_in for IPv4, sockaddr_in6 for IPv6). The data length depends on the type of address being represented. The APPARENT ADDR information element MUST be sent with IAX2 TXREQ and REGACK messages. When used with a TXREQ message, the APPARENT ADDR MUST specify the address of the peer the local peer is trying to transfer its end of the connection to. When used with a REGACK message, the APPARENT ADDR MUST specify the address it uses to reach the peer (which may be different than the address the peer perceives itself as in the case of NAT or multi-homed peer machines). The data field of the APPARENT ADDR information element is the same as the linux struct sockaddr_in: two octets for the address family, two octets for the port number, four octets for the IPv4 address, and 8 octets of padding consisting of all bits set to 0. Thus the total length of the APPARENT ADDR information element is 18 octets. The following diagram demonstrates the generic APPARENT ADDR format: 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x12 | Data Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sockaddr struct | : for address family in use : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Spencer, et al. Expires October 17, 2007 [Page 78] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 The following diagram demonstrates the APPARENT ADDR format for an IPv4 address: 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x12 | 0x10 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x0200 | <- Address family (INET) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x11d9 | <- Portno (default 4569) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 32-bit IP address | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | 8 octets of all 0s | | (padding in sockaddr_in) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The following diagram demonstrates the APPARENT ADDR format for an IPv6 address: 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x12 | 0x1C | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x0A00 | <- Address family (INET6) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x11d9 | <- Portno (default 4569) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 32 bits | <- Flow information | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 128-bit IP address | <- Ip6 Address | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 32 bits | <- Scope ID | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Spencer, et al. Expires October 17, 2007 [Page 79] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 8.4.18. REFRESH The purpose of the REFRESH information element is to indicate the number of seconds before an event expires. Its data field is 2 octets long. The REFRESH information element is used with IAX2 REGREQ, REGACK, and DPREP messages. When sent with a REGREQ it is a request that the peer maintaining the registration set the timeout to REFRESH seconds. When sent with a DPREP or REGACK, it is informational and tells a remote peer when the local peer will no longer consider the event valid. The REFRESH sent with a DPREP tells a peer how long it SHOULD store the received dialplan response. If the REFRESH information element is not received with a DPREP, the expiration of the cache data is assumed to be 10 minutes. If the REFRESH information element is not received with a REGACK, registration expiration is assumed to occur after 60 seconds. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x13 | 0x02 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 2 octets specifying refresh | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.19. DPSTATUS The purpose of the DPSTATUS information element is to indicate the status of a CALLED NUMBER in a remote dialplan. Its data field is a two octet bitmask specifying flags from the table below. Exactly one of the low 3 bits MUST be set, and zero, one, or two of the high two bits MAY be set. The DPSTATUS information element MUST be sent with IAX2 DPREP messages, as it is the payload of the dialplan response. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x14 | 0x02 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |M|R| |N|C|E| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Spencer, et al. Expires October 17, 2007 [Page 80] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 The following table lists the dialplan status flags: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | FLAG | DESCRIPTION | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x0001 | Exists | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x0002 | Can exist | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x0004 | Non-existent | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x4000 | Retain dialtone (ignorepat) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x8000 | More digits may match number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.20. CALLNO The purpose of the CALLNO information element is to indicate the call number a remote peer needs to use as a destination call number to identify a call being transferred. The peer managing a transfer sends the CALLNO for one transfer endpoint to the other transfer endpoint so that it knows what call number to specify for the transfer. The data field is 2 octets long and specifies a call number in the same manner as a source call number or destination call number is specified in a frame header. The CALLNO information element MUST be sent with IAX2 TXREQ, TXREADY, and TXREL messages. Transferring cannot succeed if the CALLNO IE is not included with the appropriate transfer messages. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x15 | 0x02 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Callno of transfer recipient | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.21. CAUSE The purpose of the CAUSE information element is to indicate the reason an event occurred. It carries a description of the CAUSE of the event as UTF-8-encoded data. Notification of the event itself is handled at the message level. Spencer, et al. Expires October 17, 2007 [Page 81] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 The CAUSE information element SHOULD be sent with IAX2 HANGUP, REJECT, REGREJ, and TXREJ messages. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x16 | Data Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : UTF-8-encoded CAUSE of event : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.22. IAX2 UNKNOWN The purpose of the IAX2 UNKNOWN information element is to indicate that a received IAX2 command was unknown or unrecognized. The one octet data field contains the subclass of the received frame that was unrecognized. The IAX2 UNKNOWN information element MUST be sent with IAX2 UNSUPPORT messages. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x17 | 0x01 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Rec'd Subclass| +-+-+-+-+-+-+-+-+ 8.4.23. MSGCOUNT The purpose of the MSGCOUNT information element is to indicate how many voicemail messages are waiting in a registered user's mailbox. The data field is 2 octets long. If it is set to all 1s, there is at least one message present. Any other value specifies the number of old messages in the high 8 bits and the number of new messages in the low 8 bits. The IAX2 MSGCOUNT information element MAY be sent with IAX2 REGACK messages. Spencer, et al. Expires October 17, 2007 [Page 82] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x18 | 0x02 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Old messages | New messages | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.24. AUTOANSWER The purpose of the AUTOANSWER information element is to request that a call be auto-answered upon receipt of a NEW message which includes the AUTOANSWER information element. Note that this is a request and may or may not be granted by the remote peer. There is no data field with this information element, as its presence alone indicates all necessary information. The AUTOANSWER information element MAY be sent with IAX2 NEW messages. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x19 | 0x00 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.25. MUSICONHOLD The purpose of the MUSICONHOLD information element is to request that music-on-hold be played while a call is in the QUELCH state. The optional data field specifies a music-on-hold class to be used, as UTF-8-encoded data. In the absence of a data field, no music-on-hold class is specified and the IE SHOULD be treated as a generic request for music-on-hold. The MUSICONHOLD information element MAY be sent with IAX2 QUELCH messages. If no MUSICONHOLD information element is received, music-on-hold is not requested. Spencer, et al. Expires October 17, 2007 [Page 83] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x1a | Data Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : Optional Music On Hold Class : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.26. TRANSFERID The purpose of the TRANSFERID information element is to identify a transfer across all three peers participating in a transfer event. It carries a number, four octets long, that SHOULD be unique for the duration of the transfer process. The TRANSFERID information element SHOULD be sent with IAX2 TXREQ and TXCNT messages to aid the peers involved in a transfer in identifying the proper calls. It is not required as long as the transferring peers can positively identify the calls participating in the transfer without the TRANSFERID. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x1b | 0x04 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 4 octet transfer | | identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.27. RDNIS The purpose of the RDNIS information element is to indicate the referring DNIS. It carries UTF-8-encoded data. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x1c | Data Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : UTF-8-encoded RDNIS : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Spencer, et al. Expires October 17, 2007 [Page 84] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 8.4.28. PROVISIONING The purpose of the PROVISIONING information element is to carry provisioning data. It carries binary data used to provision an IAX2 device. The coding scheme of the data included in the PROVISIONING IE is unspecified by the protocol, and is left to the implementor, however, it is strongly recommended that the provisioning data define its version, format, etc., to enhance interoperability. The PROVISIONING information element may only be sent with an IAX2 PROVISION message. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x1d | Data Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : Raw provisioning data : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.29. AESPROVISIONING The purpose of the AESPROVISIONING information element is to carry AES-encrypted provisioning data. It carries encrypted data used to provision an IAX2 device. The coding scheme of the data included in the AESPROVISIONING IE is unspecified by the protocol, as is left to the implementor. The AESPROVISIONING information element may only be sent with an IAX2 PROVISION message. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x1e | Data Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : AES provisioning data : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Spencer, et al. Expires October 17, 2007 [Page 85] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 8.4.30. DATETIME The DATETIME information element indicates the time a message is sent. This differs from the header time-stamp because that time- stamp begins at 0 for each call, while the DATETIME is a call- independent value representing the actual real-world time. The data field of a DATETIME information element is four octets long and stores the time as follows: The five least significant bits are seconds, the next six least significant bits are minutes, the next least significant five bits are hours, the next least significant five bits are the day of the month, the next least significant four bits are the month, and the most significant seven bits are the year. The year is offset from 2000, and the month is a 1-based index (i.e., January == 1, February == 2, etc). The timezone of the clock is undefined but UTC is recommended. The DATETIME information element SHOULD be sent with IAX2 NEW and REGACK messages. However, it is strictly informational. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x1f | 0x04 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | year | month | day | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | hours | minutes | seconds | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.31. DEVICETYPE The purpose of the DEVICETYPE information element is to indicate the type of device requesting registration or firmware downloading. It carries UTF-8-encoded data describing the type of device of the IAX2 peer. The DEVICETYPE information element MUST be sent with IAX2 FWDOWNL messages in order to help identify which firmware image is appropriate for the peer. It MAY be sent with IAX2 REGREQ messages, as well. If the initial FWDOWNL message of a call does not include the DEVICETYPE information element, the firmware download fails and a REJECT MUST be sent. If at least one FWDOWNL has been sent with a valid DEVICETYPE information element, subsequent FWDOWNL messages are not required to include it. Spencer, et al. Expires October 17, 2007 [Page 86] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x20 | Data Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : UTF-8-encoded device type : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.32. SERVICEIDENT The SERVICEIDENT information element uniquely identifies a device requesting provisioning so that appropriate data may be made available. The data field carries some guaranteed unique device identifier, e.g. the six octet hardware MAC address of the device. The SERVICEIDENT information element MAY be sent with IAX2 REGREQ messages so that an IAX2 device may be provisioned appropriately. It is never required. If the SERVICEIDENT information element is absent, a 'default' template may be used to provision the device. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x21 | 0x06 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Unique identifier | : (e.g. peer's MAC) : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.33. FIRMWAREVER The purpose of the FIRMWAREVER information element is to indicate the version of firmware an IAX2 device has. The data field is 2 octets long and specifies a firmware version the server has available for download for the received DEVICETYPE. The meaning of this value depends on the DEVICETYPE of the device. The FIRMWAREVER information element may be sent with IAX2 REGACK messages. Spencer, et al. Expires October 17, 2007 [Page 87] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x22 | 0x02 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Firmware version | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.34. FWBLOCKDESC The purpose of the FWBLOCKDESC information element is to identify a block of firmware. Sent with an FWDOWNL it is a request for the specified block of firmware. Sent with an FWDATA it is a declaration of the block of firmware included in the FWBLOCKDATA IE. The data field is 4 octets long and carries binary data. The FWBLOCKDESC information element is sent with IAX2 FWDOWNL and FWDATA messages. It can be used to acknowledge the amount of data transmitted or received. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x23 | 0x04 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Firmware Block | | Identification | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.35. FWBLOCKDATA The purpose of the FWBLOCKDATA information element is to carry a block of a firmware image from a server to an IAX2 device. The data field carries raw binary data. The FWBLOCKDATA information element is sent with IAX2 FWDATA messages. Once the firmware image is completely transmitted and acknowledged (via the FWBLOCKDESC information element), a FWDATA message containing a FWBLOCKDATA information element with no data MUST be sent to indicate that the image has been completely transmitted. Spencer, et al. Expires October 17, 2007 [Page 88] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x24 | Data Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : Binary Block of Firmware Data : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.36. PROVVER The purpose of the PROVVER information element is to indicate the provisioning version. The data field is 4 octets long and contains the version of the provisioning software used. The PROVVER information element MAY be sent with IAX2 REGREQ messages. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x25 | 0x04 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Provisioning Version | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.37. CALLINGPRES The purpose of the CALLINGPRES information element is to indicate the calling presentation of a caller. The data field is 1 octet long and contains a value from the table below. The CALLINGPRES information element MUST be sent with IAX2 NEW messages. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x26 | 0x01 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Calling Pres. | +-+-+-+-+-+-+-+-+ Spencer, et al. Expires October 17, 2007 [Page 89] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 The following table lists valid calling presentation values: +------+--------------------------------------+ | FLAG | PRESENTATION | +------+--------------------------------------+ | 0x00 | Allowed user/number not screened | | | | | 0x01 | Allowed user/number passed screen | | | | | 0x02 | Allowed user/number failed screen | | | | | 0x03 | Allowed network number | | | | | 0x20 | Prohibited user/number not screened | | | | | 0x21 | Prohibited user/number passed screen | | | | | 0x22 | Prohibited user/number failed screen | | | | | 0x23 | Prohibited network number | | | | | 0x43 | Number not available | +------+--------------------------------------+ 8.4.38. CALLINGTON The purpose of the CALLINGTON information element is to indicate the calling type of number of a caller, according to ITU-T Recommendation Q.931 specifications. The data field is 1 octet long and contains data from the table below. The CALLINGTON information element MUST be sent with IAX2 NEW messages. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x27 | 0x01 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Calling TON | +-+-+-+-+-+-+-+-+ Spencer, et al. Expires October 17, 2007 [Page 90] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 The following table lists valid calling type of number values from ITU-T Recommendation Q.931: +-------+-------------------------+ | VALUE | DESCRIPTION | +-------+-------------------------+ | 0x00 | Unknown | | | | | 0x10 | International Number | | | | | 0x20 | National Number | | | | | 0x30 | Network Specific Number | | | | | 0x40 | Subscriber Number | | | | | 0x60 | Abbreviated Number | | | | | 0x70 | Reserved for extension | +-------+-------------------------+ 8.4.39. CALLINGTNS The CALLINGTNS information element indicates the calling transit network selected for a call. Values are chosen according to ITU-T Recommendation Q.931 specifications. The data field is two octets long. The first octet stores the network identification plan in the least significant four bits according to the first table below, and the type of network in the next three least significant bits according to the second table below. The second octet stores the actual network identification in UTF-8-encoded data. The CALLINGTNS information element MUST be sent with IAX2 NEW messages. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x28 | 0x02 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | TON | Plan | UTF-8 Net ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The following tables list the valid values for the data field of the 'calling tns' IE. Spencer, et al. Expires October 17, 2007 [Page 91] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 Q.931 Network Identification Plan Values: +------+----------------------------------+ | BITS | DESCRIPTION | +------+----------------------------------+ | 0000 | Unknown | | | | | 0001 | Caller Identification Code | | | | | 0011 | Data Network Identification Code | +------+----------------------------------+ Q.931 Type of Network Values: +------+--------------------------------------+ | BITS | DESCRIPTION | +------+--------------------------------------+ | 000 | User Specified | | | | | 010 | National Network Identification | | | | | 011 | International Network Identification | +------+--------------------------------------+ 8.4.40. SAMPLINGRATE The purpose of the SAMPLINGRATE information element is to specify to a remote IAX2 peer the sampling rate in hertz of the audio data being the peer will use when sending data. Its data field is 2 octets long. If the SAMPLINGRATE information element is not specified, a default sampling rate of 8 kHz may be assumed. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x29 | 0x02 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sampling Rate in Hertz | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.41. CAUSECODE The purpose of the CAUSECODE information element is to indicate the reason a call was REJECTed or HANGUPed. It derives from ITU-T Recommendation Q.931. The data field is one octet long and contains Spencer, et al. Expires October 17, 2007 [Page 92] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 an entry from the table below. The CAUSECODE information element SHOULD be sent with IAX2 HANGUP, REJECT, REGREJ, and TXREJ messages. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x2a | 0x01 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Cause Code | +-+-+-+-+-+-+-+-+ +--------+----------------------------------------------------------+ | NUMBER | CAUSE | +--------+----------------------------------------------------------+ | 1 | Unassigned/unallocated number | | | | | 2 | No route to specified transit network | | | | | 3 | No route to destination | | | | | 6 | Channel unacceptable | | | | | 7 | Call awarded and delivered | | | | | 16 | Normal call clearing | | | | | 17 | User busy | | | | | 18 | No user response | | | | | 19 | No answer | | | | | 21 | Call rejected | | | | | 22 | Number changed | | | | | 27 | Destination out of order | | | | | 28 | Invalid number format/incomplete number | | | | | 29 | Facility rejected | | | | | 30 | Response to status enquiry | | | | | 31 | Normal, unspecified | Spencer, et al. Expires October 17, 2007 [Page 93] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 | 34 | No circuit/channel available | | | | | 38 | Network out of order | | | | | 41 | Temporary failure | | | | | 42 | Switch congestion | | | | | 43 | Access information discarded | | | | | 44 | Requested channel not available | | | | | 45 | Pre-empted (causes.h only) | | | | | 47 | Resource unavailable, unspecified (Q.931 only) | | | | | 50 | Facility not subscribed (causes.h only) | | | | | 52 | Outgoing call barred (causes.h only) | | | | | 54 | Incoming call barred (causes.h only) | | | | | 57 | Bearer capability not authorized | | | | | 58 | Bearer capability not available | | | | | 63 | Service or option not available (Q.931 only) | | | | | 65 | Bearer capability not implemented | | | | | 66 | Channel type not implemented | | | | | 69 | Facility not implemented | | | | | 70 | Only restricted digital information bearer capability is | | | available (Q.931 only) | | | | | 79 | Service or option not available (Q.931 only) | | | | | 81 | Invalid call reference | | | | | 82 | Identified channel does not exist (Q.931 only) | | | | | 83 | A suspended call exists, but this call identity does not | | | (Q.931 only) | | | | | 84 | Call identity in use (Q.931 only) | | | | Spencer, et al. Expires October 17, 2007 [Page 94] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 | 85 | No call suspended (Q.931 only) | | | | | 86 | Call has been cleared (Q.931 only) | | | | | 88 | Incompatible destination | | | | | 91 | Invalid transit network selection (Q.931 only) | | | | | 95 | Invalid message, unspecified | | | | | 96 | Mandatory information element missing (Q.931 only) | | | | | 97 | Message type nonexistent/not implemented | | | | | 98 | Message not compatible with call state | | | | | 99 | Information element nonexistent | | | | | 100 | Invalid information element contents | | | | | 101 | Message not compatible with call state | | | | | 102 | Recovery on timer expiration | | | | | 103 | Mandatory information element length error (causes.h | | | only) | | | | | 111 | Protocol error, unspecified | | | | | 127 | Internetworking, unspecified | +--------+----------------------------------------------------------+ 8.4.42. ENCRYPTION The purpose of the ENCRYPTION information element is to indicate what encryption methods are accepted for an IAX2 peer. The data field is a 2 octet bit mask specifying which encryption methods from the table below are accepted. The ENCRYPTION information element MAY be sent with IAX2 NEW and AUTHREQ messages. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x2b | 0x01 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Spencer, et al. Expires October 17, 2007 [Page 95] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 | Encryption Methods | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The following table lists valid native encryption methods: +--------+-------------+ | METHOD | DESCRIPTION | +--------+-------------+ | 0x0001 | AES-128 | +--------+-------------+ 8.4.43. ENCKEY The purpose of the ENCKEY information element is to share an encryption key with a remote peer in an already-encrypted exchange. This makes the process of rotating encryption keys simple to implement. Note that an ENCKEY may only be sent between peers that are already exchanging encrypted data. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x2c | Data Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : ENCKEY Data : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.44. CODEC PREFS The purpose of the CODEC PREFS information element is to indicate the CODEC preferences of the calling peer. The data field consists of a list of CODECs in the peer's order of preference as UTF-8-encoded data. The CODEC PREFS information element MAY be sent with IAX2 NEW messages. If the CODEC PREFS information element is absent, CODEC negotiation takes place via the CAPABILITY and FORMAT information elements. Spencer, et al. Expires October 17, 2007 [Page 96] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x2d | Data Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : CODEC Prefs Data : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.45. RR JITTER The purpose of the RR JITTER information element is to indicate the received jitter on a call, per [RFC1889]. The data field is 4 octets long and carries the current measured jitter. The RR JITTER information element MAY be sent with IAX2 PONG messages. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x2e | 0x04 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Received Jitter | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.46. RR LOSS The purpose of the RR LOSS information element is to indicate the number of lost frames on a call, per [RFC1889]. The data field is 4 octets long and carries the percentage of frames lost in the first octet, and the count of lost frames in the next 3 octets. The RR LOSS information element MAY be sent with IAX2 PONG messages. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x2f | 0x04 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Loss Percent | | +-+-+-+-+-+-+-+-+ Loss Count | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Spencer, et al. Expires October 17, 2007 [Page 97] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 8.4.47. RR PKTS The purpose of the RR PKTS information element is to indicate the total number of frames received on a call, per [RFC1889]. The data field is 4 octets long and carries the count of frames received. The RR PKTS information element MAY be sent with IAX2 PONG messages. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x30 | 0x04 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Frames Received Count | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.48. RR DELAY The purpose of the RR DELAY information element is to indicate the maximum playout delay for a call, per [RFC1889]. The data field is 2 octets long and specifies the number of milliseconds a frame may be delayed before it MUST be discarded. The RR DELAY information element MAY be sent with IAX2 PONG messages. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x31 | 0x02 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Maximum Playout Delay | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.49. RR DROPPED The purpose of the RR DROPPED information element is to indicate the total number of dropped frames for a call, per [RFC1889]. The data field is 4 octets long and carries the number of frames dropped. The RR DROPPED information element MAY be sent with IAX2 PONG messages. Spencer, et al. Expires October 17, 2007 [Page 98] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x32 | 0x04 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Total Frames Dropped | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.4.50. RR OOO The purpose of the RR OOO information element is to indicate the number of frames received out of order for a call, per [RFC1889]. The data field is 4 octets long and carries the number of frames received out of order. The RR OOO information element MAY be sent with IAX2 PONG messages. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x33 | 0x04 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Frames Received | | Out of Order | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8.5. Media Formats Spencer, et al. Expires October 17, 2007 [Page 99] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 Media Format Subclass Values +------------+-----------------+------------------------------------+ | SUBCLASS | DESCRIPTION | LENGTH CALCULATION | +------------+-----------------+------------------------------------+ | 0x00000001 | G.723.1 | 4, 20, and 24 byte frames of 240 | | | | samples | | | | | | 0x00000002 | GSM Full Rate | 33 byte chunks of 160 samples or | | | | 65 byte chunks of 320 samples | | | | | | 0x00000004 | G.711 mu-law | 1 byte per sample | | | | | | 0x00000008 | G.711 a-law | 1 byte per sample | | | | | | 0x00000010 | G.726 | | | | | | | 0x00000020 | IMA ADPCM | 1 byte per 2 samples | | | | | | 0x00000040 | 16-bit linear | 2 bytes per sample | | | little-endian | | | | | | | 0x00000080 | LPC10 | Variable size frame of 172 samples | | | | | | 0x00000100 | G.729 | 20 bytes chunks of 172 samples | | | | | | 0x00000200 | Speex | Variable | | | | | | 0x00000400 | ILBC | 50 bytes per 240 samples | | | | | | 0x00000800 | G.726 AAL2 | | | | | | | 0x00001000 | G.722 | 16kHz ADPCM | | | | | | 0x00002000 | AMR | Variable | | | | | | 0x00010000 | JPEG | | | | | | | 0x00020000 | PNG | | | | | | | 0x00040000 | H.261 | | | | | | | 0x00080000 | H.263 | | | | | | | 0x00100000 | H.263p | | | | | | | 0x00200000 | H.264 | | +------------+-----------------+------------------------------------+ Spencer, et al. Expires October 17, 2007 [Page 100] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 9. Example Message Flows This section includes call flow diagrams for some of the various types of IAX2 calls that can be made. In each diagram, the '=' character represents a full frame and the '-' character represents a mini frame. Notes applicable to a generic call may be presented alongside each diagram. 9.1. Ping/Pong PING->PONG Peer A Peer B ________________________________________ | | T | | i | ===PING============================> | m | | e | <============================PONG=== |Has same time-stamp | | as received PING. | | ===ACK=============================> |Has same time-stamp | | | as received PONG \ / |________________________________________| and original PING 9.2. Lagrq/Lagrp LAGRQ->LAGRP Peer A Peer B ________________________________________ | | T | | i | ===LAGRQ===========================> | m | | e | <===========================LAGRP=== |Same time-stamp as | | received LAGRQ. | | ===ACK=============================> |Same time-stamp as | | | received LAGRP and \ / |________________________________________| original LAGRQ. Spencer, et al. Expires October 17, 2007 [Page 101] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 9.3. Registration Registration of an IAX2 Peer Registrant A Registrar B ________________________________________ | | T | ===REGREQ==========================> | i | | m | <=========================REGAUTH=== | e | | | ===REGREQ==========================> | | | | | | <==========================REGACK=== | \ | / | | \|/ | ===ACK=============================> | | | |________________________________________| 9.4. Registration Registration Release Registrant A Registrar B ________________________________________ | | T | ===REGREL==========================> | i | | m | <=========================REGAUTH=== | e | | | ===REGREL==========================> | | | | | | <==========================REGACK=== | \ | / | | \|/ | ===ACK=============================> | | | |________________________________________| Spencer, et al. Expires October 17, 2007 [Page 102] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 9.5. Provisioning Provisioning an IAX2 Device Peer A (Provisioning server) Peer B (IAX2 Device) ________________________________________ | | T | | i | ===PROVISION=======================> |Carries m | | PROVISIONING IE e | <==========================ACCEPT=== | | | | | ===ACK=============================> | | | | \ / |________________________________________| 9.6. Firmware Download IAX2 Firmware Download Peer A (IAX2 Device) Peer B (FW manager) ________________________________________ | | T | | | ===FWDOWNL=========================> |IE spec Device Type i | . | and firmware block | . | desired. m | . | | <==========================FWDATA=== |IEs spec firmware e | . | block identifier | . | and data block | . | | | ===FWDOWNL=========================> |FWDOWNL/FWDATA | . | messages pass back | . | forth until all | . | firmware xmitted. | . | | | <==========================FWDATA=== |The last FWDATA | . | contains 0 length | . | FWBLOCKDATA IE | . | \ / | ==============================ACK==> |The last FWDATA | | MUST be ACKed. |________________________________________| Spencer, et al. Expires October 17, 2007 [Page 103] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 9.7. Call Path Optimization IAX2 Transfer Peer L Peer C Peer R ________________________________________ | | | T | | | | <== TXREQ =====[*]== TXREQ =========> |C requests transfer i | | | | ========================== TXCNT ==> |L sends to R m | | | | <========================= TXACC ==== |R replies e | | |R sends Media | | | to L | | | | | | = TXREADY ====> | |L tells C 'ready' | | | | C stops media to L | | | | | | <== TXCNT =========================== |L sends to R | | | | | | === TXACC ===========================> |R replies \ / | | | | | <== TXREADY ====== |R tells C 'ready' | | | C stops media to R | | | | <== TXREL =====[*]== TXREL =========> |C Releases | | |________________________________________| 9.8. IAX2 Media Call Complete end-to-end IAX2 media exchange Peer A Peer B ________________________________________ | | | ====NEW============================> | T | <=========================AUTHREQ=== |If authentication | | specified. i | ====AUTHREP========================> | m | <==========================ACCEPT=== | e | ====ACK============================> | | | | | <=============Voice (full frame)=== | Spencer, et al. Expires October 17, 2007 [Page 104] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 | | ====ACK===========================> | | | | | | <---------Voice miniframe (ring)--- | | | <---------Voice miniframe (ring)--- | | | | \ | / | <=========================RINGING=== | \|/ | ====ACK============================> | | | | <---------Voice miniframe (ring)--- | | <---------Voice miniframe (ring)--- | | | | <==========================ANSWER=== | | ====ACK============================> | | | | ====Voice (full frame)=============> | | <=============================ACK=== | | | | | | <-----------Voice miniframes-------> | exchange occurs | <--- . ---> | | <--- . ---> | | <--- . ---> | | <-----------Voice miniframes-------> | | | | | | ====Voice (full frame)=============> | (note 1) | <===ACK============================= | (note 2) | | (every 65536 ms). | <=============Voice (full frame)==== | (note 3) | ====ACK============================> | | | | | | <-----------Voice miniframes-------> | | <--- . ---> | | <--- . ---> | | <--- . ---> | | <-----------Voice miniframes-------> | | | | | | ====HANGUP=========================> | Either can hangup | <=============================ACK=== | |________________________________________| Note 1: Mini Frames carry the low 16 bits of the peer's 32-bit time-stamp. Note 2: Full frames re-sync the 32 bit time-stamp when the 16 bit time-stamp overflows. Spencer, et al. Expires October 17, 2007 [Page 105] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 Note 3:Each side has its own 32 bit time-stamp so each side needs to sync at 16 bit overflow. 9.9. IAX2 Media Call via an IAX2 Device An IAX2 peer is not required to maintain a complete dialplan. In the event that a user wishes to dial from an IAX2 peer which does not switch its own calls, the following call flow diagram may represent the transaction: Peer A (IAX2 Device) Peer B (Dialplan Server) ________________________________________ | | | ====NEW============================> | T | <=========================AUTHREQ=== | If auth specified i | ====AUTHREP========================> | m | <==========================ACCEPT=== | e | ====ACK============================> | | | | ====DPREQ==========================> | (Note 1) | | <===========================DPREP=== | | | | | | ====DIAL===========================> | | | <========================PROGRESS=== | | | ====ACK============================> | \ | / | <==========================ANSWER=== | \|/ | ====ACK============================> | | | | ====Voice (full frame)=============> | | <=============================ACK=== | | <=============Voice (full frame)==== | | ====ACK============================> | | | | | | <-----------Voice miniframes-------> | Media exchange | <--- . ---> | | <--- . ---> | | <--- . ---> | | <-----------Voice miniframes-------> | | | | | | ====Voice (full frame)=============> | (note 2) | <===ACK============================= | (note 3) | | (every 65536 ms). | <=============Voice (full frame)==== | (Note 4) | ====ACK============================> | Spencer, et al. Expires October 17, 2007 [Page 106] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 | | | | | <-----------Voice miniframes-------> | | <--- . ---> | | <--- . ---> | | <--- . ---> | | <-----------Voice miniframes-------> | | | | | | ====HANGUP=========================> | Either can hangup | <=============================ACK=== | |________________________________________| Note 1: There will be multiple DPREQ/DPREPs per call unless dialed number is 1 digit long Note 2: Mini Frames carry the low 16 bits of the peer's 32 bit time-stamp. Note 3: Full frames re-sync the 32 bit time-stamp when the 16 bit time-stamp overflows Note 4: Each side has its own 32 bit time-stamp so each side needs to sync at 16 bit overflow. Spencer, et al. Expires October 17, 2007 [Page 107] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 10. Security Considerations IAX2 is a binary protocol for setting up point to point call legs which includes both media and signaling. As such, it is simpler to secure than other more general purpose VoIP protocols, however, security remains a difficult task. IAX2 registration is one area that requires careful attention. Previous versions supported clear text passwords, this feature has been eliminated. The MD5 and RSA alternatives offer much higher security. Although not specified by the IAX2 protocol, some implementations limit the number of registrants per account to one. And a subsequent registrant with the same credentials would overwrite the prior and receive the calls destined for that user. Theft of service is trivial once a malicious caller has the ability to authenticate. Denial of service attacks can take at least two forms in IAX2. One is simply overloading the peers with bogus requests. A carefully implemented IAX2 peer would identify this situation and raise an alarm or take other protective action. Another form of denial of service (DoS) against an existing call is an engineered attack against an existing call. Injecting media, causing excess processing by inserting out of order packets, and sending commands such as hangup or transfer. These attacks require close monitoring of the binary channel to be successful as the message sequence numbers would need to be synchronized with the protocol exchange. Of course, using IPSEC, [RFC2401], would address many of these potential issues. Spencer, et al. Expires October 17, 2007 [Page 108] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 11. IANA Considerations This document requests registration of the "iax2" URI Scheme. See section Section 5. IAX2 also requires a well-known UDP port to be assigned. The current port in use is 4569. Spencer, et al. Expires October 17, 2007 [Page 109] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 12. Implementation Notes The original implementation of IAX2 was in Asterisk, the open-source pbx, but [wikipedia] lists thirteen other publically available implementations at the time of this writing. Many of these were developed using the source code as the only specification. While this approach is definitive, it is very difficult to determine the protocols higher level logic and optimize it for the particular programming language or application environment. Aside from the trials and tribulations of reverse engineering the code to create a new implementation, the key lessons learned involve the use of threads, support of international character sets, security, and improved controls to limit interference during denial of service attacks. The current Asterisk implementation has a limited number of IAX worker threads and, as a result, its scalability is limited, but it can run on low end machines where threads may not be freely available. Improving the threading model will undoubtedly improve performance. Internationalization and localization are issues that was not originally addressed by most implementations. It was always on the IAX2 developers' road-map, but never a priority. While creating this document, we formalized support for UTF-8 encoding to better support Internationalization and localization. With regards to security, many IAX2 implementations permit clear text authentication. This method is not secure and should not be used. Recently, some issues have been raised regarding server robustness when under a denial of service attack. IAX2 servers which support unauthenticated requests can receive the equivalent of a SYN attack. To mitigate the impact of these attacks, various controls to limit the number of unauthenticated calls and the number of calls per user may be added to the implementation. Other approaches, such as transferring the call to another, more protected, port or using IP rate limiting when excessive failures are detected, are also suggested. Lastly, given the open nature of the protocol and implementations, it is very easy to extend. This situation makes Postel's Robustness Principle, "Be conservative in what you do, be liberal in what you accept from others," essential to any successful IAX2 implementation. Spencer, et al. Expires October 17, 2007 [Page 110] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 13. Acknowledgments This work was supported by Internet Foundation Austria. The authors would like to thank Birgit Arkesteijn, Mohamed Boucadair, Steve Kann, Olle Johansson, Alexander Mayrhofer, and Tim Panton for their extensive review and technical input. We would also like to thank Christopher DeMarco, Frank Ellermann, Daniel Medeiros, Dimitri E. Prado, Leif Madson, and Tilghman Lesher for their support and suggestions. Spencer, et al. Expires October 17, 2007 [Page 111] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 14. References 14.1. Normative References [AES] U.S. Department of Commerce/N.I.S.T., "FIPS-197, Announcing the Advanced Encryption Standard", November 2001. [E164] ITU-T, "The International Public Telecommunication Number Plan", Recommendation E.164, May 1997. [RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, April 1992. [RFC1851] Karn, P., Metzger, P., and W. Simpson, "The ESP Triple DES Transform", RFC 1851, September 1995. [RFC1889] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", RFC 1889, January 1996. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2437] Kaliski, B. and J. Staddon, "PKCS #1: RSA Cryptography Specifications Version 2.0", RFC 2437, October 1998. [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, November 2003. [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005. 14.2. Informative References [RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the Internet Protocol", RFC 2401, November 1998. [RFC2833] Schulzrinne, H. and S. Petrack, "RTP Payload for DTMF Digits, Telephony Tones and Telephony Signals", RFC 2833, May 2000. Spencer, et al. Expires October 17, 2007 [Page 112] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 [RFC3761] Faltstrom, P. and M. Mealling, "The E.164 to Uniform Resource Identifiers (URI) Dynamic Delegation Discovery System (DDDS) Application (ENUM)", RFC 3761, April 2004. [RFC4395] Hansen, T., Hardie, T., and L. Masinter, "Guidelines and Registration Procedures for New URI Schemes", BCP 115, RFC 4395, February 2006. [wikipedia] http://en.wikipedia.org/wiki/IAX, "Inter-Asterisk eXchange". Spencer, et al. Expires October 17, 2007 [Page 113] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 Authors' Addresses Mark A. Spencer Digium, Inc. 150 West Park Loop Suite 100 Huntsville, AL 35806 US Phone: +1 256 428 6000 Email: markster@digium.com URI: http://www.digium.com/ Brian Capouch Saint Joseph's College PO Box 909 Rensselaer, IN 47978 US Phone: +1 219 866 6114 Email: brianc@saintjoe.edu Ed Guy (editor) TruPhone 235 Main Street, STE 253 Madison, NJ 07940 US Phone: +1 973 437 4519 Email: edguy@emcsw.com URI: http://www.TruPhone.com/ Frank Miller Cornfed Systems, Inc. 103 Overhill Road Baltimore, MD 21210 US Phone: +1 410 404-8790 Email: fwmiller@cornfed.com URI: http://www.digium.com/ Spencer, et al. Expires October 17, 2007 [Page 114] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 Kenneth C. Shumard 3818 N Lakegrove Way Boise, ID 83713 US Phone: +1 208 724 7801 Email: kshumard@gmail.com Spencer, et al. Expires October 17, 2007 [Page 115] Internet-Draft IAX2: Inter-Asterisk eXchange Version 2 April 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Spencer, et al. Expires October 17, 2007 [Page 116]