Internet Engineering Task Force (IETF) F. Andreasen Request for Comments: 5898 Cisco Systems Category: Standards Track G. Camarillo ISSN: 2070-1721 Ericsson D. Oran D. Wing Cisco Systems July 2010 Connectivity Preconditions for Session Description Protocol (SDP) Media Streams Abstract This document defines a new connectivity precondition for the Session Description Protocol (SDP) precondition framework. A connectivity precondition can be used to delay session establishment or modification until media stream connectivity has been successfully verified. The method of verification may vary depending on the type of transport used for the media. For unreliable datagram transports such as UDP, verification involves probing the stream with data or control packets. For reliable connection-oriented transports such as TCP, verification can be achieved simply by successful connection establishment or by probing the connection with data or control packets, depending on the situation. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc5898.
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Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Connectivity Precondition Definition . . . . . . . . . . . . . 4 3.1. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.2. Operational Semantics . . . . . . . . . . . . . . . . . . 4 3.3. Status Type . . . . . . . . . . . . . . . . . . . . . . . 5 3.4. Direction Tag . . . . . . . . . . . . . . . . . . . . . . 5 3.5. Precondition Strength . . . . . . . . . . . . . . . . . . 5 4. Verifying Connectivity . . . . . . . . . . . . . . . . . . . . 6 4.1. Correlation of Dialog to Media Stream . . . . . . . . . . 7 4.2. Explicit Connectivity Verification Mechanisms . . . . . . 7 4.3. Verifying Connectivity for Connection-Oriented Transports . . . . . . . . . . . . . . . . . . . . . . . . 9 5. Connectivity and Other Precondition Types . . . . . . . . . . 9 6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 7. Security Considerations . . . . . . . . . . . . . . . . . . . 14 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15 9.1. Normative References . . . . . . . . . . . . . . . . . . . 15 9.2. Informative References . . . . . . . . . . . . . . . . . . 16 1. Introduction The concept of a Session Description Protocol (SDP) [RFC4566] precondition in the Session Initiation Protocol (SIP) [RFC3261] is defined in RFC 3312 [RFC3312] (updated by RFC 4032 [RFC4032]). A precondition is a condition that has to be satisfied for a given media stream in order for session establishment or modification to proceed. When the precondition is not met, session progress is delayed until the precondition is satisfied or the session establishment fails. For example, RFC 3312 [RFC3312] defines the Quality of Service precondition, which is used to ensure availability of network resources prior to establishing a session (i.e., prior to starting to alert the callee). SIP sessions are typically established in order to set up one or more media streams. Even though a media stream may be negotiated successfully through an SDP offer-answer exchange, the actual media stream itself may fail. For example, when there is one or more Network Address Translators (NATs) or firewalls in the media path, the media stream may not be received by the far end. In cases where the media is carried over a connection-oriented transport such as TCP [RFC0793], the connection-establishment procedures may fail. The connectivity precondition defined in this document ensures that session progress is delayed until media stream connectivity has been verified.
The connectivity precondition type defined in this document follows the guidelines provided in RFC 4032 [RFC4032] to extend the SIP preconditions framework. 2. 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 [RFC2119]. 3. Connectivity Precondition Definition 3.1. Syntax The connectivity precondition type is defined by the string "conn", and hence we modify the grammar found in RFC 3312 [RFC3312] and RFC 5027 [RFC5027] as follows: precondition-type = "conn" / "sec" / "qos" / token This precondition tag is registered with the IANA in Section 8. 3.2. Operational Semantics According to RFC 4032 [RFC4032], documents defining new precondition types need to describe the behavior of UAs (User Agents) from the moment session establishment is suspended due to a set of preconditions, until it is resumed when these preconditions are met. An entity that wishes to delay session establishment or modification until media stream connectivity has been established uses this precondition-type in an offer. When a mandatory connectivity precondition is received in an offer, session establishment or modification is delayed until the connectivity precondition has been met (i.e., until media stream connectivity has been established in the desired direction or directions). The delay of session establishment defined here implies that alerting of the called party does not occur until the precondition has been satisfied. Packets may be both sent and received on the media streams in question. However, such packets SHOULD be limited to packets that are necessary to verify connectivity between the two endpoints involved on the media stream. That is, the underlying media stream SHOULD NOT be cut through. For example, Interactive Connectivity Establishment (ICE) connectivity checks [RFC5245] and TCP SYN, SYN- ACK, and ACK packets can be exchanged on media streams that support them as a way of verifying connectivity.
Some media streams are described by a single 'm' line but, nevertheless, involve multiple addresses. For example, RFC 5109 [RFC5109] specifies how to send FEC (Forward Error Correction) information as a separate stream (the address for the FEC stream is provided in an 'a=fmtp' line). When a media stream consists of multiple destination addresses, connectivity to all of them MUST be verified in order for the precondition to be met. In the case of RTP media streams [RFC3550] that use RTCP, connectivity MUST be verified for both RTP and RTCP; the RTCP transmission interval rules MUST still be adhered to. 3.3. Status Type RFC 3312 [RFC3312] defines support for two kinds of status types -- namely, segmented and end-to-end. The connectivity precondition-type defined here MUST be used with the end-to-end status type; use of the segmented status type is undefined. 3.4. Direction Tag The direction attributes defined in RFC 3312 [RFC3312] are interpreted as follows: o send: the party that generated the session description is sending packets on the media stream to the other party, and the other party has received at least one of those packets. That is, there is connectivity in the forward (sending) direction. o recv: the other party is sending packets on the media stream to the party that generated the session description, and this party has received at least one of those packets. That is, there is connectivity in the backwards (receiving) direction. o sendrecv: both the send and recv conditions hold. Note that a "send" connectivity precondition from the offerer's point of view corresponds to a "recv" connectivity precondition from the answerer's point of view, and vice versa. If media stream connectivity in both directions is required before session establishment or modification continues, the desired status needs to be set to "sendrecv". 3.5. Precondition Strength Connectivity preconditions may have a strength-tag of either "mandatory" or "optional".
When a mandatory connectivity precondition is offered and the answerer cannot satisfy the connectivity precondition (e.g., because the offer does not include parameters that enable connectivity to be verified without media cut through) the offer MUST be rejected as described in RFC 3312 [RFC3312]. When an optional connectivity precondition is offered, the answerer MUST generate its answer SDP as soon as possible. Since session progress is not delayed in this case, it is not known whether the associated media streams will have connectivity. If the answerer wants to delay session progress until connectivity has been verified, the answerer MUST increase the strength of the connectivity precondition by using a strength-tag of "mandatory" in the answer. Note that use of a mandatory precondition requires the presence of a SIP "Require" header with the option tag "precondition". Any SIP UA that does not support a mandatory precondition will reject such requests. To get around this issue, an optional connectivity precondition and the SIP "Supported" header with the option tag "precondition" can be used instead. Offers with connectivity preconditions in re-INVITEs or UPDATEs follow the rules given in Section 6 of RFC 3312 [RFC3312]. That is: Both user agents SHOULD continue using the old session parameters until all the mandatory preconditions are met. At that moment, the user agents can begin using the new session parameters. 4. Verifying Connectivity Media stream connectivity is ascertained by use of a connectivity verification mechanism between the media endpoints. A connectivity verification mechanism may be an explicit mechanism, such as ICE [RFC5245] or ICE TCP [ICE-TCP], or it may be an implicit mechanism, such as TCP. Explicit mechanisms provide specifications for when connectivity between two endpoints using an offer/answer exchange is ascertained, whereas implicit mechanisms do not. The verification mechanism is negotiated as part of the normal offer/answer exchange; however, it is not identified explicitly. More than one mechanism may be negotiated, but the offerer and answerer need not use the same. The following rules guide which connectivity verification mechanism to use: o If an explicit connectivity verification mechanism (e.g., ICE) is negotiated, the precondition is met when the mechanism verifies connectivity successfully.
o Otherwise, if a connection-oriented transport (e.g., TCP) is negotiated, the precondition is met when the connection is established. o Otherwise, if an implicit verification mechanism is provided by the transport itself or the media stream data using the transport, the precondition is met when the mechanism verifies connectivity successfully. o Otherwise, connectivity cannot be verified reliably, and the connectivity precondition will never be satisfied if requested. This document does not mandate any particular connectivity verification mechanism; however, in the following, we provide additional considerations for verification mechanisms. 4.1. Correlation of Dialog to Media Stream SIP and SDP do not provide any inherent capabilities for associating an incoming media stream packet with a particular dialog. Thus, when an offerer is trying to ascertain connectivity, and an incoming media stream packet is received, the offerer may not know which dialog had its "recv" connectivity verified. Explicit connectivity verification mechanisms therefore typically provide a means to correlate the media stream, whose connectivity is being verified, with a particular SIP dialog. However, some connectivity verification mechanisms may not provide such a correlation. In the absence of a mechanism for the correlation of dialog to media stream (e.g., ICE), a UAS (User Agent Server) MUST NOT require the offerer to confirm a connectivity precondition. 4.2. Explicit Connectivity Verification Mechanisms Explicit connectivity verification mechanisms typically use probe traffic with some sort of feedback to inform the sender whether reception was successful. Below we provide two examples of such mechanisms, and how they are used with connectivity preconditions: Interactive Connectivity Establishment (ICE) [RFC5245] provides one or more candidate addresses in signaling between the offerer and the answerer and then uses STUN (Simple Traversal of the UDP Protocol through NAT) Binding Requests to determine which pairs of candidate addresses have connectivity. Each STUN Binding Request contains a password that is communicated in the SDP as well; this enables correlation between STUN Binding Requests and candidate addresses for a particular media stream. It also provides correlation with a particular SIP dialog.
ICE implementations may be either full or lite (see [RFC5245]). Full implementations generate and respond to STUN Binding Requests, whereas lite implementations only respond to them. With ICE, one side is a controlling agent, and the other side is a controlled agent. A full implementation can take on either role, whereas a lite implementation can only be a controlled agent. The controlling agent decides which valid candidate to use and informs the controlled agent of it by identifying the pair as the nominated pair. This leads to the following connectivity precondition rules: o A full implementation ascertains both "send" and "recv" connectivity when it operates as a STUN client and has sent a STUN Binding Request that resulted in a successful check for all the components of the media stream (as defined further in ICE). o A full or a lite implementation ascertains "recv" connectivity when it operates as a STUN server and has received a STUN Binding Request that resulted in a successful response for all the components of the media stream (as defined further in ICE). o A lite implementation ascertains "send" and "recv" connectivity when the controlling agent has informed it of the nominated pair for all the components of the media stream. A simpler and slightly more delay-prone alternative to the above rules is for all ICE implementations to ascertain "send" and "recv" connectivity for a media stream when the ICE state for that media stream has moved to Completed. Note that there is never a need for the answerer to request confirmation of the connectivity precondition when using ICE: the answerer can determine the status locally. Also note, that when ICE is used to verify connectivity preconditions, the precondition is not satisfied until connectivity has been verified for all the component transport addresses used by the media stream. For example, with an RTP-based media stream where RTCP is not suppressed, connectivity MUST be ascertained for both RTP and RTCP. Finally, it should be noted, that although connectivity has been ascertained, a new offer/ answer exchange may be required before media can flow (per ICE). The above are merely examples of explicit connectivity verification mechanisms. Other techniques can be used as well. It is however RECOMMENDED that ICE be supported by entities that support connectivity preconditions. Use of ICE has the benefit of working for all media streams (not just RTP) as well as facilitating NAT and firewall traversal, which may otherwise interfere with connectivity. Furthermore, the ICE recommendation provides a baseline to ensure
that all entities that require probe traffic to support the connectivity preconditions have a common way of ascertaining connectivity. 4.3. Verifying Connectivity for Connection-Oriented Transports Connection-oriented transport protocols generally provide an implicit connectivity verification mechanism. Connection establishment involves sending traffic in both directions thereby verifying connectivity at the transport-protocol level. When a three-way (or more) handshake for connection establishment succeeds, bi-directional communication is confirmed and both the "send" and "recv" preconditions are satisfied whether requested or not. In the case of TCP for example, once the TCP three-way handshake has completed (SYN, SYN-ACK, ACK), the TCP connection is established and data can be sent and received by either party (i.e., both a send and a receive connectivity precondition has been satisfied). SCTP (Stream Control Transmission Protocol) [RFC4960] connections have similar semantics as TCP and SHOULD be treated the same. When a connection-oriented transport is part of an offer, it may be passive, active, or active/passive [RFC4145]. When it is passive, the offerer expects the answerer to initiate the connection establishment, and when it is active, the offerer wants to initiate the connection establishment. When it is active/passive, the answerer decides. As noted earlier, lack of a media-stream-to-dialog correlation mechanism can make it difficult to guarantee with whom connectivity has been ascertained. When the offerer takes on the passive role, the offerer will not necessarily know which SIP dialog originated an incoming connection request. If the offerer instead is active, this problem is avoided. 5. Connectivity and Other Precondition Types The role of a connectivity precondition is to ascertain media stream connectivity before establishing or modifying a session. The underlying intent is for the two parties to be able to exchange media packets successfully. However, connectivity by itself may not fully satisfy this. Quality of Service, for example, may be required for the media stream; this can be addressed by use of the "qos" precondition defined in RFC 3312 [RFC3312]. Similarly, successful security parameter negotiation may be another prerequisite; this can be addressed by use of the "sec" precondition defined in RFC 5027 [RFC5027].
6. Examples The first example uses the connectivity precondition with TCP in the context of a session involving a wireless access medium. Both UAs use a radio access network that does not allow them to send any data (not even a TCP SYN) until a radio bearer has been set up for the connection. Figure 1 shows the message flow of this example (the required PRACK transaction has been omitted for clarity -- see [RFC3312] for details): A B | INVITE | | a=curr:conn e2e none | | a=des:conn mandatory e2e sendrecv | | a=setup:holdconn | |----------------------------------->| | | | 183 Session Progress | | a=curr:conn e2e none | | a=des:conn mandatory e2e sendrecv | | a=setup:holdconn | |<-----------------------------------| | | | UPDATE | | a=curr:conn e2e none | | a=des:conn mandatory e2e sendrecv | A's radio | a=setup:actpass | bearer is +----------------------------------->| up | | | 200 OK | | a=curr:conn e2e none | | a=des:conn mandatory e2e sendrecv | | a=setup:active | |<-----------------------------------| | | | | | | | | B's radio |<---TCP Connection Establishment--->+ bearer is up | | B sends TCP SYN | | | | | 180 Ringing | TCP connection |<-----------------------------------+ is up | | B alerts the user | | Figure 1: Message Flow with Two Types of Preconditions
A sends an INVITE requesting connection-establishment preconditions. The setup attribute in the offer is set to holdconn [RFC4145] because A cannot send or receive any data before setting up a radio bearer for the connection. B agrees to use the connectivity precondition by sending a 183 (Session Progress) response. The setup attribute in the answer is also set to holdconn because B, like A, cannot send or receive any data before setting up a radio bearer for the connection. When A's radio bearer is ready, A sends an UPDATE to B with a setup attribute with a value of actpass. This attribute indicates that A can perform an active or a passive TCP open. A is letting B choose which endpoint will initiate the connection. Since B's radio bearer is not ready yet, B chooses to be the one initiating the connection and indicates this with a setup attribute with a value of active. At a later point, when B's radio bearer is ready, B initiates the TCP connection towards A. Once the TCP connection is established successfully, B knows the "sendrecv" precondition is satisfied, and B proceeds with the session (i.e., alerts the Callee), and sends a 180 (Ringing) response. The second example shows a basic SIP session establishment using SDP connectivity preconditions and ICE (the required PRACK transaction and some SDP details have been omitted for clarity). The offerer (A) is a full ICE implementation whereas the answerer (B) is a lite ICE implementation. The message flow for this scenario is shown in Figure 2 below.
A B | | |-------------(1) INVITE SDP1--------------->| | | |<------(2) 183 Session Progress SDP2--------| | | |~~~~~ Connectivity check to B ~~~~~~~~~~~~~>| |<~~~~ Connectivity to B OK ~~~~~~~~~~~~~~~~~| | | |-------------(3) UPDATE SDP3--------------->| | | |<--------(4) 200 OK (UPDATE) SDP4-----------| | | |<-------------(5) 180 Ringing---------------| | | | | Figure 2: Connectivity Precondition with ICE Connectivity Checks SDP1: A includes a mandatory end-to-end connectivity precondition with a desired status of "sendrecv"; this will ensure media stream connectivity in both directions before continuing with the session setup. Since media stream connectivity in either direction is unknown at this point, the current status is set to "none". A's local status table (see [RFC3312]) for the connectivity precondition is as follows: Direction | Current | Desired Strength | Confirm -----------+----------+------------------+---------- send | no | mandatory | no recv | no | mandatory | no and the resulting offer SDP is: a=ice-pwd:asd88fgpdd777uzjYhagZg a=ice-ufrag:8hhY m=audio 20000 RTP/AVP 0 c=IN IP4 192.0.2.1 a=rtcp:20001 a=curr:conn e2e none a=des:conn mandatory e2e sendrecv a=candidate:1 1 UDP 2130706431 192.0.2.1 20000 typ host SDP2: When B receives the offer, B sees the mandatory sendrecv connectivity precondition. B is a lite ICE implementation and hence B can only ascertain "recv" connectivity (from B's point of view)
from A; thus, B wants A to inform it about connectivity in the other direction ("send" from B's point of view). B's local status table therefore looks as follows: Direction | Current | Desired Strength | Confirm -----------+----------+------------------+---------- send | no | mandatory | no recv | no | mandatory | no Since B is a lite ICE implementation and B wants to ask A for confirmation about the "send" (from B's point of view) connectivity precondition, the resulting answer SDP becomes: a=ice-lite a=ice-pwd:qrCA8800133321zF9AIj98 a=ice-ufrag:H92p m=audio 30000 RTP/AVP 0 c=IN IP4 192.0.2.4 a=rtcp:30001 a=curr:conn e2e none a=des:conn mandatory e2e sendrecv a=conf:conn e2e send a=candidate:1 1 UDP 2130706431 192.0.2.4 30000 typ host Since the "send" and the "recv" connectivity precondition (from B's point of view) are still not satisfied, session establishment remains suspended. SDP3: When A receives the answer SDP, A notes that B is a lite ICE implementation and that confirmation was requested for B's "send" connectivity precondition, which is the "recv" precondition from A's point of view. A performs a successful send and recv connectivity check to B by sending an ICE connectivity check to B and receiving the corresponding response. A's local status table becomes: Direction | Current | Desired Strength | Confirm -----------+----------+------------------+---------- send | yes | mandatory | no recv | yes | mandatory | yes whereas B's local status table becomes: Direction | Current | Desired Strength | Confirm -----------+----------+------------------+---------- send | no | mandatory | no recv | yes | mandatory | no
Since B asked for confirmation about the "recv" connectivity (from A's point of view), A now sends an UPDATE (5) to B to confirm the connectivity from A to B: a=ice-pwd:asd88fgpdd777uzjYhagZg a=ice-ufrag:8hhY m=audio 20000 RTP/AVP 0 c=IN IP4 192.0.2.1 a=rtcp:20001 a=curr:conn e2e sendrecv a=des:conn mandatory e2e sendrecv a=candidate:1 1 UDP 2130706431 192.0.2.1 20000 typ host B knows it has recv connectivity (verified by ICE as well as A's UPDATE) and send connectivity (confirmed by A's UPDATE) at this point. B's local status table becomes: Direction | Current | Desired Strength | Confirm -----------+----------+------------------+---------- send | yes | mandatory | no recv | yes | mandatory | no and the session can continue. 7. Security Considerations General security considerations for preconditions are discussed in RFC 3312 [RFC3312] and RFC 4032 [RFC4032]. As discussed in RFC 4032 [RFC4032], it is strongly RECOMMENDED that S/MIME [RFC3853] integrity protection be applied to the SDP session descriptions. When the user agent provides identity services (rather than the proxy server), the SIP identity mechanism specified in RFC 4474 [RFC4474] provides an alternative end-to-end integrity protection. Additionally, the following security issues relate specifically to connectivity preconditions. Connectivity preconditions rely on mechanisms beyond SDP, such as TCP [RFC0793] connection establishment or ICE connectivity checks [RFC5245], to establish and verify connectivity between an offerer and an answerer. An attacker that prevents those mechanisms from succeeding (e.g., by keeping ICE connectivity checks from arriving at their destination) can prevent media sessions from being established. While this attack relates to connectivity preconditions, it is actually an attack against the connection-establishment mechanisms used by the endpoints. This attack can be performed in the presence or in the absence of connectivity preconditions. In their presence, the whole session setup will be disrupted. In their absence, only the establishment of the particular stream under attack will be
disrupted. This specification does not provide any mechanism against attackers able to block traffic between the endpoints involved in the session because such an attacker will always be able to launch DoS (Denial-of-Service) attacks. Instead of blocking the connectivity checks, the attacker can generate forged connectivity checks that would cause the endpoints to assume that there was connectivity when there was actually no connectivity. This attack would result in the user experience being poor because the session would be established without all the media streams being ready. The same attack can be used, regardless of whether or not connectivity preconditions are used, to attempt to hijack a connection. The forged connectivity checks would trick the endpoints into sending media to the wrong direction. To prevent these attacks, it is RECOMMENDED that the mechanisms used to check connectivity are adequately secured by message authentication and integrity protection. For example, Section 2.5 of [RFC5245] discusses how message integrity and data origin authentication are implemented in ICE connectivity checks. 8. IANA Considerations IANA has registered a new precondition type under the Precondition Types used with SIP subregistry, which is located under the Session Initiation Protocol (SIP) Parameters registry. Precondition-Type Description Reference ----------------- ----------------------------------- --------- conn Connectivity precondition [RFC5898] 9. References 9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [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. [RFC3312] Camarillo, G., Marshall, W., and J. Rosenberg, "Integration of Resource Management and Session Initiation Protocol (SIP)", RFC 3312, October 2002.
[RFC3853] Peterson, J., "S/MIME Advanced Encryption Standard (AES) Requirement for the Session Initiation Protocol (SIP)", RFC 3853, July 2004. [RFC4032] Camarillo, G. and P. Kyzivat, "Update to the Session Initiation Protocol (SIP) Preconditions Framework", RFC 4032, March 2005. [RFC4474] Peterson, J. and C. Jennings, "Enhancements for Authenticated Identity Management in the Session Initiation Protocol (SIP)", RFC 4474, August 2006. [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session Description Protocol", RFC 4566, July 2006. [RFC5027] Andreasen, F. and D. Wing, "Security Preconditions for Session Description Protocol (SDP) Media Streams", RFC 5027, October 2007. [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT) Traversal for Offer/Answer Protocols", RFC 5245, April 2010. 9.2. Informative References [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, September 1981. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, July 2003. [RFC4145] Yon, D. and G. Camarillo, "TCP-Based Media Transport in the Session Description Protocol (SDP)", RFC 4145, September 2005. [RFC4960] Stewart, R., "Stream Control Transmission Protocol", RFC 4960, September 2007. [RFC5109] Li, A., "RTP Payload Format for Generic Forward Error Correction", RFC 5109, December 2007. [ICE-TCP] Perreault, S., Ed. and J. Rosenberg, "TCP Candidates with Interactive Connectivity Establishment (ICE)", Work in Progress, October 2009.
Authors' Addresses Flemming Andreasen Cisco Systems, Inc. 499 Thornall Street, 8th Floor Edison, NJ 08837 USA EMail: firstname.lastname@example.org Gonzalo Camarillo Ericsson Hirsalantie 11 Jorvas 02420 Finland EMail: Gonzalo.Camarillo@ericsson.com David Oran Cisco Systems, Inc. 7 Ladyslipper Lane Acton, MA 01720 USA EMail: email@example.com Dan Wing Cisco Systems, Inc. 170 West Tasman Drive San Jose, CA 95134 USA EMail: firstname.lastname@example.org