Reason Header in Responses June 2007 BLISS Roland Jesske Internet Draft Deutsche Telekom Intended Status: private Document: draft-jesske-sipping-etsi-ngn-reason-01.txt Expires: December 2007 June 2007 Use of the Reason header field in Session Initiation Protocol (SIP) responses draft-jesske-sipping-etsi-ngn-reason-01.txt 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. 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 December 6, 2007. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract This document proposes the use of the Reason header field in SIP responses. In addition for the interoperability wit DSS1 interworked devices and the ISUP a Location fild is defined in addition. Jesske Expires - December 2007 [Page 1] Reason Header in Responses June 2007 Table of Contents 1. Overview.......................................................2 2. Overall Applicability..........................................2 3. Terminology....................................................3 4. Procedures.....................................................3 4.1 Procedures at the UA.......................................3 4.2 Procedures at a SIP proxy..................................3 4.3 Procedures at an application server........................3 5. Procedures at an interworking point with ISUP..................4 6. Example........................................................4 7. Security Considerations........................................5 8. IANA Considerations............................................5 9. References.....................................................5 1. Overview The European Telecommunication Standards Institute (ETSI) is defining a Next Generation Network (NGN) where a substantial part of it is based on the IP Multimedia Subsystem (IMS) defined by the Third- Generation Partnership Project (3GPP). IMS is largely based on the Session Initiation Protocol [1]. ETSI has developed a number of requirements draft-jesske-sipping- tispan-requirements [5] to support the usage of SIP in Next Generation Networks that interoperate, at the service level, with the Public Switched Telephone Network (PSTN), the Integrated Services Digital Network (ISDN), the 3GPP IP Multimedia Subsystem (IMS), and SIP networks and terminals that implement the service logic. In order to provide full support in SIP of existing services, extensions to SIP are needed. This document proposes the use of the Reason header field in responses. This is needed for creating services that must be interoperable with the PSTN/ISDN network and the interoperability of traversing communications through SIP not using SIP-I. This fulfils the requirement [REQ-GEN-1 in draft-jesske-sipping-tispan- requirements [5]] 2.Overall Applicability The SIP procedures specified in this document are foreseen for networks providing simulation services and/or interworking to the PSTN/ISDN. Jesske Expires - December 2007 [Page 2] Reason Header in Responses June 2007 The document is describing the use of the Reason header in SIP responses. These procedures are only valuable if the reason contained in the element "protocol" is "Q.850". A inclusion of a SIP reason (protocol="SIP") is not helpful due to the fact that the response already provides the SIP reason. The Release Causes are described within ETSI EN300 485 [5] 3. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119. [9]. 4. Procedures For providing services and PSTN/ISDN interoperability for SIP networks it MUST be possible to include Reason header fields with Q.850 Cause values in responses. 4.1 Procedures at the UA A UA that supports the Reason header field can process the Q.850 Cause Value and display it or an equivalent text. The inclusion of a Reason header field by UA is only for 2B2 UA interworking with the PSTN/ISDN or providing PSTN/ISDN like services foreseen. For a pure SIP UA the reason header will not harm if not supported because it will not be processed. For SIP end devices the support of the Reason header field the cause maybe an valuable hint why the call was released by an non SIP entity. 4.2 Procedures at a SIP proxy SIP proxies that receive a response containing a Reason header field is forwarding the response without changing the reason. A SIP proxy receiving a request that includes a Reason header field can route the request to an application server for further analysis and base services on it. Based on network policy a Proxy can remove a Reason header field send from a UAC. 4.3 Procedures at an application server An application server that receives a SIP request that contains a response including a Reason header MAY analyze the SIP Reason and base further procedures on this analyses. Jesske Expires - December 2007 [Page 3] Reason Header in Responses June 2007 For Example the application server could use the reason for sending a announcement towards the originating entity of the Session. If the application server provides a Service it can provide also Responses include a Q.850 reason in responses. 5. Procedures at an interworking point with ISUP For interoperability reasons the Q.850 Cause Value of a Release shall be mapped to the Reason Header. 6. Example Figure 1 shows the example of SIP interworking with the PSTN/ISDN A Gateway Proxy AS | IAM | | | |------------------>| INVITE | | | |----------------->| INVITE | | | 100 Trying |----------------->| | |<-----------------| 100 Trying | | | |<-----------------| | ACK SDP held | | | |<------------------| | 603 Decline | | | 603 Decline | Reason Q850 #87 | | | Reason Q850 #87 | | | REL Cause #87 | |<-----------------| | |<-----------------| | |<----------------- | | | | | | | | | | | | | | | Figure 1: Example of an ISDN like service executed within the SIP domain Figure 2 shows the example of SIP interworking with the PSTN/ISDN where the call is traversed through the SIP network A Gateway Gateway B | IAM | | | |------------------>| INVITE | | | |----------------->| IAM | | | 100 Trying |----------------->| | | | REL Cause #29 | | | 500 Server Error | | | | Reason Q850 #29 | | Jesske Expires - December 2007 [Page 4] Reason Header in Responses June 2007 | REL Cause #29 | |<-----------------| | |<-----------------| | |<----------------- | | | | | | | | | | | Figure 1: Example of an ISDN - SIP - ISDN Call 7. Security Considerations The presence of the Reason header in a response does not affect the treatment of the response. Including such a header by an untrusted entity could adulterate the reactions of the originating entities. E.G. sending back a cause value "87" can cause an announcement within the PSTN/ISDN saying that the call was rejected due to the Closed User Group service. Therefore it is RECOMMENDED to include the Reason header only by trusted entities as it is described within RFC3325 [8] or at least by network entities. 8. IANA Considerations This document describes the use of the Reason header field described within RFC 3326 [2]. No additional SIP elements are defined within this document. Therefore, this document does not provide any action to IANA. 9. References [1] 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. [2] H. Schulzrinne, D. Oran, G. Camarillo, "The Reason Header for the Session Initiation Protocol (SIP)", RFC 3326. [3] Jesske, R., Alexeitsev, D., Garcia-Martin, M. "Input Require- ments for the Session Initiation Protocol (SIP) in support for the European Telecommunications Standards Institute (ETSI) Next Generation Network (NGN) simulation services", draft-jesske- sipping-tispan-requirements-04.txt (work in progress), June 2007. [4] 3GPP TS 24.229: "IP Multimedia Call Control Protocol based on SIP and SDP". Jesske Expires - December 2007 [Page 5] Reason Header in Responses June 2007 [5] ETSI EN 300 485: "Integrated Services Digital Network (ISDN); Dfinition and usage of cause and location in Digital Subscriber Signalling System No. one (DSS1) and Signalling System No. 7 (SS7) ISDN User Part (ISUP) [ITU-T Recommendation Q.850 (1998) with addendum modified] ". [6] Jesske, R., Alexeitsev, D., Garcia-Martin, M. "Analysis of the Input Requirements for the Session Initiation Protocol (SIP) in support for the European Telecommunications Standards Institute (ETSI) Next Generation Networks (NGN) simulation services" (work in progress) June 2005 [8] Jennings C., Peterson J., and Watson M. "Private Extensions to the Session Initiation Protocol (SIP) for Asserted Identity within Trusted Networks", RFC 3325, November 2002. [9] RFC2119 Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels," BCP 14, RFC 2119, March 1997 (TXT, HTML, XML). Note: The ETSI specifications can be downloaded under http://pda.etsi.org/pda/queryform.asp free of charge. Contributors Denis Alexeitsev Deutsche Telekom Deutsche Telekom Allee1 64307 Darmstadt Germany Phone: +496151832130 Email: d.alexeitsev@t-com.net Acknowledgments The author would like to thank the members of the ETSI TISPAN WG3 for their comments to this memo. Author's Addresses Roland Jesske Deutsche Telekom Deutsche Telekom Allee1 64307 Darmstadt Jesske Expires - December 2007 [Page 6] Reason Header in Responses June 2007 Germany Phone: +496151835940 Email: r.jesske@t-com.net 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. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 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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 Jesske Expires - December 2007 [Page 7] Reason Header in Responses June 2007 Administrative Support Activity (IASA). Jesske Expires - December 2007 [Page 8]