MMUSIC J. Rosenberg Internet-Draft Cisco Systems Expires: April 26, 2007 October 23, 2006 TCP Candidates with Interactive Connectivity Establishment (ICE draft-ietf-mmusic-ice-tcp-02 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 April 26, 2007. Copyright Notice Copyright (C) The Internet Society (2006). Abstract Interactive Connectivity Establishment (ICE) defines a mechanism for NAT traversal for multimedia communication protocols based on the offer/answer model of session negotiation. ICE works by providing a set of candidate transport addresses for each media stream, which are then validated with peer-to-peer connectivity checks based on Simple Traversal of UDP over NAT (STUN). ICE provides a general framework for describing alternates, but only defines UDP-based transport protocols. This specification extends ICE to TCP-based media, including the ability to offer a mix of TCP and UDP-based candidates Rosenberg Expires April 26, 2007 [Page 1] Internet-Draft ICE October 2006 for a single stream. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Overview of Operation . . . . . . . . . . . . . . . . . . . . 4 3. Sending the Initial Offer . . . . . . . . . . . . . . . . . . 5 3.1. Gathering Candidates . . . . . . . . . . . . . . . . . . . 5 3.2. Prioritization . . . . . . . . . . . . . . . . . . . . . . 7 3.3. Choosing In-Use Candidates . . . . . . . . . . . . . . . . 8 3.4. Encoding the SDP . . . . . . . . . . . . . . . . . . . . . 8 4. Receiving the Initial Offer . . . . . . . . . . . . . . . . . 8 4.1. Forming the Check Lists . . . . . . . . . . . . . . . . . 8 5. Connectivity Checks . . . . . . . . . . . . . . . . . . . . . 9 5.1. Client Procedures . . . . . . . . . . . . . . . . . . . . 9 5.1.1. Sending the Request . . . . . . . . . . . . . . . . . 9 5.2. Server Procedures . . . . . . . . . . . . . . . . . . . . 10 6. Concluding ICE . . . . . . . . . . . . . . . . . . . . . . . . 10 7. Subsequent Offer/Answer Exchanges . . . . . . . . . . . . . . 10 7.1. Generating the Offer . . . . . . . . . . . . . . . . . . . 10 7.2. Receiving the Offer and Generating the Answer . . . . . . 10 7.3. Updating the Check and Valid Lists . . . . . . . . . . . . 11 8. Media Handling . . . . . . . . . . . . . . . . . . . . . . . . 11 8.1. Sending Media . . . . . . . . . . . . . . . . . . . . . . 11 8.2. Receiving Media . . . . . . . . . . . . . . . . . . . . . 11 9. Connection Management . . . . . . . . . . . . . . . . . . . . 12 10. Security Considerations . . . . . . . . . . . . . . . . . . . 12 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 13.1. Normative References . . . . . . . . . . . . . . . . . . . 13 13.2. Informative References . . . . . . . . . . . . . . . . . . 13 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14 Intellectual Property and Copyright Statements . . . . . . . . . . 15 Rosenberg Expires April 26, 2007 [Page 2] Internet-Draft ICE October 2006 1. Introduction Interactive Connectivity Establishment (ICE) [6] defines a mechanism for NAT traversal for multimedia communication protocols based on the offer/answer model [2] of session negotiation. ICE works by providing a set of candidate transport addresses for each media stream, which are then validated with peer-to-peer connectivity checks based on Simple Traversal of UDP over NAT (STUN) [1]. ICE provides a general framework for describing alternates, but only defines procedures for UDP-based transport protocols. There are many reasons why ICE support for TCP and TCP/TLS is important. Firstly, there are media protocols that only run over TCP or TCP/TLS. Examples of such protocols are web and application sharing and instant messaging [9]. For these protocols to work in the presence of NAT, unless they define their own NAT traversal mechanisms, ICE support for TCP and TCP/TLS is needed. In addition, RTP itself can run over TCP [4] and TCP/TLS [5]. Typically, it is preferable to run RTP over UDP, and not TCP or TCP/TLS. However, in a variety of network environments, overly restrictive NAT and firewall devices prevent UDP-based communications altogether, but general TCP-based communications are permitted. In such environments, sending RTP over TCP or TCP/TLS, and thus establishing the media session, may be preferable to having it fail altogether. With ICE, agents can gather UDP, TCP and TCP/TLS candidates for an RTP-based stream, list the UDP ones with higher priority, and then only use the TCP-based ones if the UDP ones fail altogether. This provides a fallback mechanism that allows multimedia communications to be highly reliable. The usage of RTP over TCP is particularly useful when combined with the STUN relay usage [7]. In that usage, one of the agents would connect to its STUN relay server using TCP, and obtain a TCP-based allocated address. It would offer this to its peer agent as a candidate. The answerer would initiate a TCP connection towards the STUN relay server. When that connection is established, media can flow over the connections, through the relay. The benefit of this usage is that it only requires the agents to make outbound TCP connections to a server on the public network. This kind of operation is broadly interoperable through NAT and firewall devices. Since it is a goal of ICE and this extension to provide highly reliable communications that "just works" in as a broad a set of network deployments as possible, this usage is particularly important. The usage of RTP over TCP/TLS is useful when communicating between single-user agents (such as a softphone or hardphone) and a publicly connected device, like a PSTN gateway. In this case, the PSTN Rosenberg Expires April 26, 2007 [Page 3] Internet-Draft ICE October 2006 gateway would act as the TLS server, and have a certificate. The client can then connect, validate the certificate, but offer none of its own (since its not likely to have one). STUN itself would then provide authentication of the softphone to the gateway, leveraging the exchange of a short term credential in the SIP signaling. This specification extends ICE by defining its usage with TCP and TCP/TLS based candidates. This specification does so by following the outline of ICE itself, and calling out the additions and changes necessary in each section of ICE to support TCP and TCP/TLS candidates. 2. Overview of Operation The usage of ICE with TCP and TCP/TLS is relatively straightforward. The main area of specification is around how and when connections are opened, and how those connections relate to candidate pairs. When the agents perform address allocations to gather TCP-based candidates, three types of candidates can be obtained. These are active candidates, passive candidates, and simultaneous-open candidates [3]. An active candidate is one for which the agent will attempt to open an outbound connection, but will not receive incoming connection requests. A passive candidate is one for which the agent will receive incoming connection attempts, but not attempt a connection. A simultaneous-open candidate is one for which the agent will attempt to open a connection simultaneously with its peer. These same three types are defined for TCP/TLS. When gathering candidates from a host interface, the agent typically obtains an active, passive and simultaneous-open candidates. Similarly, communications with a STUN server will provide server reflexive and relayed versions of all three types. When encoding these candidates into offers and answers, the type of the candidate is signaled. In the case of active candidates, an IP address and port is present, but it is meaningless, as it is ignored by the peer. As a consequence, active candidates do not need to be physically allocated at the time of address gathering. Rather, the physical allocations, which occur as a consequence of a connection attempt, occur at the time of the connectivity checks. When the candidates are paired together, active candidates are always paired with passive, and simultaneous-open candidates with each other. When a connectivity check is to be made for a transport address pair within a candidate pair, each agent determines whether it is to make a connection attempt for this pair. Rosenberg Expires April 26, 2007 [Page 4] Internet-Draft ICE October 2006 Why have both active and actpass candidates for local and relayed transport addresses? Why not just simultaneous-open? The reason is that NAT treatment of simultaneous opens is currently not well defined, though specifications are being developed to address this [8]. Some NATs generate block the second TCP SYN packet or improperly process the subsequent SYNACK, which will cause the connection attempt to fail. Therefore, if only simultaneous opens are used, connections may often fail. However, only doing unidirectional opens (where one side is active and the other is passive) is more reliable, but will always require a relay if both sides are behind NAT. Therefore, in the spirit of the ICE philosophy, both are tried. Simultaneous-opens are preferred since, if it does work, it will not require a relay even when both sides are behind a different NAT. The actual processing of generating connectivity checks, managing the state of the check list, and updating the Valid list, work identically for TCP and TCP/TLS as they do for UDP. ICE requires an agent to demultiplex STUN and application layer traffic, since they appear on the same port. This demultiplexing is described by ICE, and is done using the magic cookie and other fields of the message. Stream-oriented transports introduce another wrinkle, since they require a way to frame the connection so that the application and STUN packets can be extracted in order to determine which is which. For this reason, TCP or TCP/TLS media streams utilizing ICE use the basic framing provided in RFC 4571 [4], even if the application layer protocol is not RTP. When an updated offer is generated by the controlling endpoint, the SDP extensions for connection oriented media [3] are used to signal that an existing connection should be used, rather than opening a new one. 3. Sending the Initial Offer 3.1. Gathering Candidates For each TCP capable media stream the agent wishes to use (including ones, like RTP, which can either be UDP or TCP), the agent SHOULD obtain two host candidates for each component of the media stream on each interface that the host has - one for the simultaneous open, and one for the passive candidate. If the agent is capable of acting as a server in TLS connections, it SHOULD do the same for each TCP/TLS capable media stream that the agent wishes to use (such as RTP). Providers of real-time communications services may decide that it is Rosenberg Expires April 26, 2007 [Page 5] Internet-Draft ICE October 2006 preferable to have no media at all than it is to have media over TCP. To allow for choice, it is RECOMMENDED that agents be configurable with whether they obtain TCP candidates for real time media. Having it be configurable, and then configuring it to be off, is far better than not having the capability at all. An important goal of this specification is to provide a single mechanism that can be used across all types of endpoints. As such, it is preferable to account for provider and network variation through configuration, instead of hard-coded limitations in an implementation. Furthermore, network characteristics and connectivity assumptions can, and will change over time. Just because a agent is communicating with a server on the public network today, doesn't mean that it won't need to communicate with one behind a NAT tomorrow. Just because a agent is behind a NAT with endpoint indpendent mapping today, doesn't mean that tomorrow they won't pick up their agent and take it to a public network access point where there is a NAT with address and port dependent mapping properties, or one that only allows outbound TCP. The way to handle these cases and build a reliable system is for agents to implement a diverse set of techniques for allocating addresses, so that at least one of them is almost certainly going to work in any situation. Implementors should consider very carefully any assumptions that they make about deployments before electing not to implement one of the mechanisms for address allocation. In particular, implementors should consider whether the elements in the system may be mobile, and connect through different networks with different connectivity. They should also consider whether endpoints which are under their control, in terms of location and network connectivity, would always be under their control. In environments where mobility and user control are possible, a multiplicity of techniques is essential for reliability. Each agent SHOULD "obtain" an active host candidate for each component of each TCP and TCP/TLS capable media stream on each interface that the host has. The agent does not have to actually allocate a port for these candidates. These candidates serve as a placeholder for the creation of the check lists. Using each simultaneous-open and passive host TCP candidate as a base, the agent SHOULD obtain both a relayed and server reflexive candidate using the STUN relay usage. The relay usage allows the agent to ask for a UDP or TCP-based relayed candidate when connecting to the server using TCP or TLS. It is RECOMMENDED that a TCP-based host candidate be used to obtain a TCP-based relayed candidate. An agent MAY use an additional host TCP candidate to request a UDP-based candidate from the server. Usage of the UDP candidate from the relay follows the procedures defined in ICE for UDP candidates. Rosenberg Expires April 26, 2007 [Page 6] Internet-Draft ICE October 2006 Using each simultaneous-open and passive host TCP/TLS candidate as a base, the agent SHOULD obtain a server reflexive TCP/TLS candidate using the STUN Binding Discovery usage. Each agent SHOULD "obtain" an active relayed candidate for each component of each TCP and TCP/TLS capable media stream on each interface that the host has. The agent does not have to actually allocate a port for these candidates from the relay at this time. These candidates serve as a placeholder for the creation of the check lists. Like its UDP counterparts, TCP-based STUN transactions are paced out at one every Ta seconds. This pacing refers to the establishment of a TCP connection to the STUN server and the subsequent STUN request. That is, every Ta seconds, the agent will open a new TCP connection and send a STUN request, ideally an Allocate request, since it will provide multiple candidates with one request. 3.2. Prioritization The transport protocol itself is a criteria for choosing one candidate over another. If a particular media stream can run over UDP or TCP, the UDP candidates might be preferred over the TCP candidates. This allows ICE to use the lower latency UDP connectivity if it exists, but fallback to TCP if UDP doesn't work. To accomplish this, the local preference SHOULD be defined as: local-preference = (2^12)*(transport-pref) + (2^9)*(direction-pref) + (2^0)*(other-pref) When this formulation is used, the transport-pref MUST be between 0 and 15, with 15 being the most preferred. The direction-pref MUST be between 0 and 7, with 7 being the most preferred. Other-pref MUST be between 0 and 511, with 511 being the most preferred. For RTP-based media streams, it is RECOMMENDED that UDP have a transport-pref of 15, TCP of 10, and TLS of 4. It is RECOMMENDED that, for all connection-oriented media, simultaneous-open candidates have a direction-pref of 7, active of 5 and passive of 2. If any two candidates have the same type-preference, transport-pref, and direction-pref, they MUST have a unique other-pref. With this specification, the only way that can happen is with multi-homed hosts, in which case other-pref is a preference amongst interfaces. Rosenberg Expires April 26, 2007 [Page 7] Internet-Draft ICE October 2006 3.3. Choosing In-Use Candidates The In-Use candidate is chosen primarily based on the likelihood of it working with a non-ICE peer. When media streams supporting mixed modes (both TCP and UDP) are used with ICE, it is RECOMMENDED that, for real-time streams (such as RTP), the operating candidate be UDP- based. 3.4. Encoding the SDP TCP-based candidates are encoded into a=candidate lines identically to the UDP encoding described in [6]. However, the transport protocol is set to "tcp-so" for TCP simultaneous-open candidates, "tcp-act" for TCP active candidates, "tcp-pass" for TCP passive candidates, "tls-so" for TCP/TLS simultaneous-open candidates, "tls- act" for TCP/TLS active candidates, and "tls-pass" for TCP/TLS passive candidates. The addr and port encoded into the candidate attribute for active candidates MUST be set to IP address that will be used for the attempt, but the port MUST be set to 9 (i.e., Discard). For relayed candidates, the IP address that will be used for the attempt is the one from a passive or simultaneous-open candidate from the same STUN server. If the in-use candidate is TCP or TCP/TLS, the agent MUST include the parameters defined in RFC 4145 [3] and RFC 4572 [5] respectively, as they will be needed for a non-ICE peer. If the in-use candidate is not TCP or TCP/TLS, but there are TCP or TCP/TLS candidates present for a media stream, those parameters MUST NOT be included. The rules in this specification define an alternative set of procedures for connection management for TCP; for TCP/TLS, the subsequent offer/ answer is used to verify the TLS certificate fingerprint, should that candidate be selected. This is discussed in more detail below. 4. Receiving the Initial Offer 4.1. Forming the Check Lists When forming candidate pairs, the following types of candidates can be paired with each other: Rosenberg Expires April 26, 2007 [Page 8] Internet-Draft ICE October 2006 Local Remote Candidate Candidate ---------------------------- tcp-so tcp-so tcp-act tcp-pass tcp-pass tcp-act tls-so tls-so tls-act tls-pass tls-pass tls-act When the agent prunes the check list, it MUST also remove any pair for which the local candidate is either tcp-pass or tls-pass. The remainder of check list processing works like the UDP case. 5. Connectivity Checks 5.1. Client Procedures 5.1.1. Sending the Request When an agent wants to send a TCP or TCP/TLS-based connectivity check, it first opens a TCP connection if none yet exists for the 5-tuple on which the check is to be sent. This connection is opened from the local candidate of the check to the remote candidate of the check. If the local candidate is tls-act or tcp-act, the agent MUST open a connection from the interface associated with that local candidate. This connection MUST be opened from an unallocated port. For host candidates, this is readily done by connecting from the specific interface. For relayed candidates, the agent uses the procedures in [7] to initiate a new connection from the specified interface on the relay. [[TODO: need to make sure this reconciles with latest TURN]]. If the pair is TLS-based, and the local candidate is tls-so, the agent MUST offer a client certificate. Note, however, that there will not have been an a=fingerprint attribute yet in the offer/answer exchange unless the candidate pair is a match for the in-use pair. Consequently, once the TLS exchange completes, certificate validation as described in RFC 4572 is not yet done. Once the TCP or TCP/TLS connection is established, connectivity checks are sent over the connection. The agent MUST use the framing defined in RFC 4571 [4], even though the data will include both media (possibly RTP) and STUN packets. This framing MUST be used for the lifetime of this connection. Rosenberg Expires April 26, 2007 [Page 9] Internet-Draft ICE October 2006 If the TCP connection cannot be established, or the TLS handshakes fail, the check is considered to have failed, and a full-mode agent MUST update its state to Failed in the check list. 5.2. Server Procedures An agent MUST be prepared to receive incoming TCP connection requests on any host or relayed TCP or TCP/TLS candidate that is simultaneous- open or passive. When the connection request is received, the agent MUST accept it. If the candidate on which the connection was received is a TCP/TLS candidate, the agent MUST proceed with TLS negotiation. It MUST offer a certificate. As discussed above, validation of the fingerprint does not yet happen. The agent MUST use the framing defined in RFC 4571 [4], even though the data will include both media (possibly RTP) and STUN packets. This framing MUST be used for the lifetime of this connection. Once the connection is established, server procedures are identical to those for UDP candidates. Note that STUN requests received on a passive TCP or TCP/TLS candidate will typically produce a remote peer reflexive candidate. 6. Concluding ICE If the candidate pairs selected for media by ICE are TCP/TLS, the controlling agent MUST send an updated offer if the previous offer did not include a fingerprint attribute, even if those candidates match the values in the m/c-line. 7. Subsequent Offer/Answer Exchanges 7.1. Generating the Offer If an agent places a selected TCP or TCP/TLS candidate in the m/c- line of a subsequent offer, if MUST include the a=holdconn attribute from RFC 4145, since an in-use connection is being used. However, the a=active, a=passive and a=actpass attributes are not needed. For TLS candidates, the offer MUST also include the fingerprint attribute defined in RFC 4572. 7.2. Receiving the Offer and Generating the Answer The same rules for inclusion of the RFC 4145 and RFC 4572 attributes apply to the answerer as they do to the offerer. Furthermore, for TLS candidates in the m/c-line, the agent MUST verify the fingerprint Rosenberg Expires April 26, 2007 [Page 10] Internet-Draft ICE October 2006 when the subsequent offer arrives. 7.3. Updating the Check and Valid Lists If an ICE restart occurs for a media stream with TCP or TCP/TLS candidates, the agents MUST close each connection except for the ones in-use by ICE for sending media. Those connections continue to be used for media while ICE checks re-run (establishing new connections in the process). 8. Media Handling 8.1. Sending Media When sending media, if the 5-tuple to which media is sent (the base of the local candidate and the remote candidate) match an existing TCP connection, that connection is used for sending media. The framing defined in RFC 4571 MUST be used when sending media. For media streams that are not RTP-based and do not normally use RFC 4571, the agent treats the media stream as a byte stream, and assumes that it has its own framing of some sort. It then takes an arbitrary number of bytes from the bytestream, and places that as a payload in the RFC 4571 frames, including the length. The recipient can extract the bytestream and apply the application-specific framing on it. If the candidate pair selected by ICE for usage with media is TCP/ TLS, and an updated offer has not yet been received containing the fingerprint attribute, the agent MUST NOT send media on that connection. Once the fingerprints have been validated, the agent MAY send media. 8.2. Receiving Media The framing defined in RFC 4571 MUST be used when receiving media. For media streams that are not RTP-based and do not normally use RFC 4571, the agent extracts the payload of each RFC 4571 frame, and determines if it is a STUN or an application layer data based on the procedures in [6]. If it is application layer data, the agent appends this to the ongoing bytestream collected from the frames. It then parses the bytestream as if it had been directly received over the TCP or TCP/TLS connection. This allows for ICE-tcp to work without regard to the framing mechanism used by the application layer protocol. If the candidate pairs selected by ICE include TCP/TLS candidates, and an updated offer/answer exchange has not yet occurred to exchange Rosenberg Expires April 26, 2007 [Page 11] Internet-Draft ICE October 2006 and validate the fingerprint, the agent MUST NOT accept media over that connection until the fingerprints have been validated. [[TODO: Hmm, seems like a race here; we'll lose the first few packets the answerer sends until its answer is received]] 9. Connection Management Once a TCP or TCP/TLS connection is opened by ICE, its lifecycle depends on how it is used. If that candidate pair is selected by ICE for usage for media, the connection stays open until either the session terminates, the media stream is removed, or an ICE restart takes place, resulting in the selection of a different candidate pair. If that candidate pair is not selected by ICE for usage with media, an agent SHOULD close the connection once ICE processing reaches the Completed state for that media stream. If a connection is in use for either media or checks, and the connection closes for some reason, and the local candidate is either active or simultaneous-open, the agent SHOULD reopen the connection. Unlike RFC 4145, additional signaling is not required to repair a closed connection. 10. Security Considerations The main threat in ICE is hijacking of connections for the purposes of directing media streams to DoS targets or to malicious users. ICE-tcp prevents that by only using TCP connections that have been validated. Validation requires a STUN transaction to take place over the connection. This transaction cannot complete without both participants knowing a shared secret exchanged in the rendezvous protocol used with ICE, such as SIP. This shared secret, in turn, is protected by that protocol exchange. In the case of SIP, the usage of the sips mechanism is RECOMMENDED. When this is done, an attacker, even if it knows or can guess the port on which an agent is listening for incoming TCP connections, will not be able to open a connection and send media to the agent. A more detailed analysis of this attack and the various ways ICE prevents it are described in [6]. Those considerations apply to this specification. 11. IANA Considerations There are no IANA considerations associated with this specification. Rosenberg Expires April 26, 2007 [Page 12] Internet-Draft ICE October 2006 12. Acknowledgements The authors would like to thank Tim Moore, Francois Audet and Roni Even for the reviews and input on this document. 13. References 13.1. Normative References [1] Rosenberg, J., "Simple Traversal Underneath Network Address Translators (NAT) (STUN)", draft-ietf-behave-rfc3489bis-04 (work in progress), July 2006. [2] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with Session Description Protocol (SDP)", RFC 3264, June 2002. [3] Yon, D. and G. Camarillo, "TCP-Based Media Transport in the Session Description Protocol (SDP)", RFC 4145, September 2005. [4] Lazzaro, J., "Framing Real-time Transport Protocol (RTP) and RTP Control Protocol (RTCP) Packets over Connection-Oriented Transport", RFC 4571, July 2006. [5] Lennox, J., "Connection-Oriented Media Transport over the Transport Layer Security (TLS) Protocol in the Session Description Protocol (SDP)", RFC 4572, July 2006. [6] Rosenberg, J., "Interactive Connectivity Establishment (ICE): A Methodology for Network Address Translator (NAT) Traversal for Offer/Answer Protocols", draft-ietf-mmusic-ice-11 (work in progress), October 2006. [7] Rosenberg, J., "Obtaining Relay Addresses from Simple Traversal Underneath NAT (STUN)", draft-ietf-behave-turn-02 (work in progress), October 2006. 13.2. Informative References [8] Guha, S., "NAT Behavioral Requirements for TCP", draft-ietf-behave-tcp-01 (work in progress), June 2006. [9] Campbell, B., "The Message Session Relay Protocol", draft-ietf-simple-message-sessions-15 (work in progress), July 2006. Rosenberg Expires April 26, 2007 [Page 13] Internet-Draft ICE October 2006 Author's Address Jonathan Rosenberg Cisco Systems 600 Lanidex Plaza Parsippany, NJ 07054 US Phone: +1 973 952-5000 Email: jdrosen@cisco.com URI: http://www.jdrosen.net Rosenberg Expires April 26, 2007 [Page 14] Internet-Draft ICE October 2006 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. 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Disclaimer of Validity 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 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. Copyright Statement Copyright (C) The Internet Society (2006). 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. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Rosenberg Expires April 26, 2007 [Page 15]