MMUSIC Working Group F.
AndreasonAndreasen Internet-Draft Cisco System, Inc. Expires: October 26, 2005April 22, 2006 G. Camarillo Ericsson D. Oran Cisco Systems, Inc D. Wing Cisco Systems, Inc. April 24,October 19, 2005 Connectivity Preconditions for Session Description Protocol Media Streams draft-ietf-mmusic-connectivity-precon-00.txtdraft-ietf-mmusic-connectivity-precon-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 October 26, 2005.April 22, 2006. Copyright Notice Copyright (C) The Internet Society (2005). Abstract This document defines a new connectivity precondition for the Session Description Protocol precondition framework described in RFC 3312 (and its update, RFC4032). A connectivity precondition can be used to delay session establishment or modification until media stream connectivity has been verified successfully. The method of verification may vary depending on the type of transport used for the media. For reliable connection-oriented transports such as TCP verification is achieved by successful connection establishment. For unreliable datagram transports such as UDP, verification involves probing the stream with data or control packets. NOTE: This document is the result of a merge of two prior documents with overlapping scope: draft-ietf-mmusic-connectivityprecondition-02 and draft-ietf-mmusic-connection-precon-02. The former covered the case of datagram unreliable transports; the latter the case of connection-oriented reliable transports. The merged version covers these two but also describes operations in hybrid cases of unreliable connection-oriented transports and reliable datagram transports.Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 43 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 43 3. Connectivity Precondition Definition . . . . . . . . . . . . . 4 3.13 3.1. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.23 3.2. Operational semantics . . . . . . . . . . . . . . . . . . 5 3.34 3.3. Status type . . . . . . . . . . . . . . . . . . . . . . . 5 3.44 3.4. Direction tag . . . . . . . . . . . . . . . . . . . . . . 5 3.54 3.5. Precondition strength . . . . . . . . . . . . . . . . . . 65 4. Verifying connectivity . . . . . . . . . . . . . . . . . . . . 7 4.16 4.1. Procedures for connection-oriented transports . . . . . . 8 4.27 4.2. Procedures for datagram transports . . . . . . . . . . . . 8 5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 6. Security Considerations . . . . . . . . . . . . . . . . . . . 14 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15 8.18.1. Normative References . . . . . . . . . . . . . . . . . . . 15 8.28.2. Informative References . . . . . . . . . . . . . . . . . . 15 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 16. . 17 Intellectual Property and Copyright Statements . . . . . . . . 17. . 18 1. Introduction The concept of a Session Description Protocol (SDP)  precondition in the Session Initiation Protocol (SIP) [SIP] is defined in RFC3312  (updated by 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, RFC3312 defines the Quality of Service precondition, which is used to ensure availability of network resources prior to establishing (i.e. alerting) a call. SIP sessions are typically established in order to setup 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 ,, 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, or the session itself is abandoned. The connectivity precondition type defined in this document follows the guidelines provided in RFC4032  to extend the SIP preconditions framework. 2. Terminology In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119  and indicate requirement levels for compliant implementations. 3. Connectivity Precondition Definition 3.13.1. Syntax The connectivity precondition type is defined by the string "conn" and hence we modify the grammar found in RFC 3312 as follows: precondition-type = "conn" | "qos" | token This precondition tag is registered with the IANA in Section 7. 3.23.2. Operational semantics According to RFC4032 , documents defining new precondition types need to describe the behavior of UAs from the moment session establishment is suspended due to a set of preconditions until 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., media stream connectivity has been established in the desired direction(s). 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, i.e. the underlying media stream SHOULD NOT be cut through. For example, STUN packets [STUN], RTP No-Op packets and corresponding RTCP reports, as well as TCP SYN and ACK packets can be exchanged on media streams that support them as a way of verifying connectivity. When the 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-based media streams, RTCP connectivity however is not a requirement. 3.33.3. Status type RFC 3312 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. 3.43.4. Direction tag The direction attributes defined in RFC 3312 are interpreted as follows: o send: The party who generated the session description (the offerer in an offer-answer exchange) is sending packets on the media stream to the other party, and the other party has received at least one of those packets, i.e., there is connectivity in the forward (sending) direction. o recv: The other party (the answerer in an offer-answer exchange) is sending packets on the media stream to this party, and this party has received at least one of those packets, i.e., there is connectivity in the backwards (receiving) direction. o sendrecv: Both the send and recv conditions hold. In the case of a connection-oriented transport such as TCP, once established the connection would usually have an associated direction tag of sendrecv because it can carry data in both directions. 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 MUST be set to "sendrecv". 3.53.5. 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. 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, i.e.: "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." It should be noted, that connectivity may not exist between two entities initially, e.g., when one or both entities are behind a symmetric NAT. Subsequent packet exchanges however may create the necessary address bindings in the NAT(s) thereby creating connectivity. The ICE  methodology for example ensures that such bindings are created following an offer/answer exchange. 4. Verifying connectivity The above definitions of send and receive connectivity preconditions beg two questions: How does the sender of a packet know the other party received it, and how does the receiver of a packet know who sent it (in particular, the correlation between an incoming media packet and a particular SIP dialog may not be obvious).obvious) ? Media stream connectivity can be ascertained in a variety of ways. This document does not mandate any particular mechanism for doing so, however the appropriate machinery is likely to vary depending on the type of transport used for media carriage. In order to comply with the intent of an endpoint requiring connectivity preconditions, the following general principles apply: o The 3-way handshake connection establishment procedures of a reliable transport protocol such as TCP are usually adequate to demonstrate bi-directional connectivity (and hence "sendrecv" media capability). Probe packets sent over the connection are generally not required to satisfy the precondition. o A pure datagram transport such as UDP (whether carrying RTP or some other protocol) by itself provides no useful feedback about connectivity. Hence, some sort of probe traffic is necessary to ascertain whether packets are being received successfully. o Connectivity preconditions are used to verify connectivity based on the address information exchanged in offers and answers. When overlapping IP address spaces are used (e.g. because one or both endpoints are behind a Network Address Translator), it is possible to inadvertently verify connectivity with an unrelated entity. In order to address this issue, a correlation mechanism is needed between media stream packets on one side and offers and answers on the other side. ICE  defines one such correlation mechanism, however use of it is above and beyond the connection-oriented connectivity preconditions defined here. o Some connection-oriented transport protocols may allow the data transfer phase to operate in an unreliable mode (today there is no standards-track IETF protocol which exhibits this characteristic). In such cases the success of connection establishment may not definitively demonstrate connectivity in the data phase, and hence probe traffic MAY be necessary to ascertain if the precondition is met. o Hybrid protocols such as DCCP  provide their own feedback channel and initialization procedures, which can serve to verify connectivity without the use of explicit probe traffic. The determination depends on the exact method being used to verify connectivity. 4.14.1. Procedures for connection-oriented transports TCP connections are bidirectional and hence there is no difference between send and recv connectivity preconditions. Once the TCP three-way hand shake 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. Implementations SHOULD NOT require the receipt of probe traffic in order to consider the precondition satisfied. SCTP  connections have similar semantics as TCP and SHOULD be treated the same as TCP. 4.2 Procedures for datagram transports VerificationWhen a connection-oriented transport is part of connectivity on datagram transports usually entailan offer, it may be passive, active, or active/passive . When it is passive, the sending of probe traffic with some form of feedbackofferer expects the answerer to informinitiate the sender whether reception was successful. Any ofconnection establishment, and when it is active, the following techniques MAY be used. Other techniques which meetofferer wants to initiate the requirement of Section 4 above MAY also be used. o RTP no-op : The sender of an RTP No-Op payload can verify send connectivity by examiningconnection establishment. When it is active/passive, the RTCP report(s) being returned. Inanswerer decides. SIP and SDP do not provide any inherent capabilities for associating an incoming media stream packet with a particular dialog. Thus, when the offerer is passive and an incoming connection is being established, the offerer cannot guarantee that the packet is associated with a particular dialog. When SIP forking is being used, this implies that the offerer cannot determine which of the early dialogs now has its recv connectivity precondition satisfied - a correlation mechanism is missing. This turns out not to be a problem however, since the successful completion of the connection- establishment procedure itself (e.g. receipt of SYN-ACK in the case of TCP) informs the answerer that the precondition has been satisfied, and hence there is no need for the offerer to explicitly inform the answerer of this (by sending a SIP UPDATE message). In the absence of a correlation mechanism (e.g. ICE), an answerer therefore MUST NOT require the offerer to confirm a connectivity precondition on a connection-oriented transport. 4.2. Procedures for datagram transports Verification of connectivity on datagram transports usually entails the sending of probe traffic with some form of feedback to inform the sender whether reception was successful. Techniques that can be used to verify connectivity on datagram transports include: o ICE : ICE provides one or more candidate addresses in signaling between the offerer and the answerer and then uses STUN Binding Requests to determine which pairs of candidate addresses have connectivity. Each STUN Binding Request contains a password which is communicated in the SDP as well; this enables correlation between STUN Binding Requests and candidate addresses for a particular media stream. In ICE, connectivity is always checked in both directions by following a state machine with a set of states for the offerer and a set of states for the answerer: The offerer ascertains "recv" connectivity for a particular transport address pair by transitioning into the "validating" state, whereas "send" connectivity is ascertained by transitioning into the "valid" state. The answerer ascertains both "send" and "recv" connectivity for a particular transport address pair by transitioning into the "send-valid" state. As a consequence of this, 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. When ICE is used to verify connectivity preconditions, the precondition is satisfied as soon as one of the candidates becomes valid, i.e. 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; this is a tightening of the general operational semantics provided in Section 3.2 imposed by ICE. Finally, it should be noted, that though connectivity has been ascertained, a new offer/answer exchange may be required before media can actually flow (per ICE). o RTP no-op : The sender of an RTP No-Op payload can verify send connectivity by examining the RTCP report(s) being returned. In particular, the source SSRC in the RTCP report block is used for correlation. The RTCP report block also contains the SSRC of the sender of the report and the SSRC of incoming RTP No-Op packets identifies the sender of the RTP packet. Thus, once send connectivity has been ascertained, receipt of an RTP No-Op packet from the same SSRC provides the necessary correlation to determine receive connectivity. Alternatively, the duality of send and receive preconditions can be exploited, with one side confirming when his send precondition is satisfied, which in turn implies the other sides recv precondition is satisfied. o STUN :The STUN binding request message sent to check connectivity contains a transaction ID which is returned in the STUN binding response, thus send connectivity is verified easily. STUN binding requests also contain a username and a password which ICE  communicates via SIP. When an incoming STUN message is received, it is therefore easy to determine the sourceabove are merely examples of techniques that message and hence receive connectivitycan be determined that way. ICE presents the peer with a number of alternative candidate addresses for a particular media stream. Once connectivity has been verified for one of those candidate addresses, connectivity has been verified, regardless of whether this candidate address is the one that ends up beingused. If a media stream consists of multiple destination addresses, verification of a candidate address for each must occur in order forOther techniques which meet the precondition torequirements of Section 4 above can be satisfied.used as well. It is however RECOMMENDED that the No-Op RTP payload formatICE be supported by entities that support connectivity preconditions. This willpreconditions for datagram transports. Use of ICE has the benefit of working for all datagram based media streams (not just RTP) as well as facilitate 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 at least one common way of ascertaining connectivity. 5. 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 setup for the connection. Figure 1 shows the message flow of this example (the PRACK transaction has been omitted for clarity): 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 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 so 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 alerts the callee and sends a 180 (Ringing) response. The second example shows a basic SIP session establishment using SDP connectivity preconditions and RTP No-Op. Note that not all SDP details are provided in the following. below shows the message flow for this scenario shown in Figure 2 below. A B | | |-------------(1) INVITE SDP1--------------->| | | |<------(2) 183 Session Progress SDP2--------| | | |<~~~~~ Connectivity check to A ~~~~~~~~~~~~~| | | |----------------(3) PRACK------------------>| | | |~~~~~ Connectivity to A OK ~~~~~~~~~~~~~~~~>| | | |<-----------(4) 200 OK (PRACK)--------------| | | |~~~~~ Connectivity check to B ~~~~~~~~~~~~~>| |<~~~~ Connectivity to B OK ~~~~~~~~~~~~~~~~~| | | |-------------(5) UPDATE SDP3--------------->| | | |<--------(6) 200 OK (UPDATE) SDP4-----------| | | |<-------------(7) 180 Ringing---------------| | | | | | | Figure 2: Connectivity precondition with RTP no-op 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 RFC 3312) 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: m=audio 20000 RTP/AVP 0 96 c=IN IP4 192.0.2.1 a=rtpmap:96 no-op/8000 a=curr:conn e2e none a=des:conn mandatory e2e sendrecv SDP2: When B receives the offer, B sees the mandatory sendrecv connectivity precondition. B can ascertain connectivity to A ("send" from B's point of view) by use of the RTP No-Op, however B wants A to inform it about connectivity in the other direction ("recv" 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 wants to ask A for confirmation about the "recv" (from B's point of view) connectivity precondition, the resulting answer SDP becomes: m=audio 30000 RTP/AVP 0 96 a=rtpmap:96 no-op/8000 c=IN IP4 192.0.2.4 a=curr:conn e2e none a=des:conn mandatory e2e sendrecv a=conf:conn e2e recv Meanwhile, B performs a connectivity check to A, which succeeds and hence B's local status table is updated as follows: Direction | Current | Desired Strength | Confirm -----------+----------+------------------+---------- send | yes | mandatory | no recv | no | mandatory | no Since the "recv" connectivity precondition (from B's point of view) is still not satisfied, session establishment remains suspended. SDP3: When A receives the answer SDP, A notes that confirmation was requested for B's "recv" connectivity precondition, which is the "send" precondition from A's point of view. A performs a connectivity check to B, which succeeds, and A's local status table becomes: Direction | Current | Desired Strength | Confirm -----------+----------+------------------+---------- send | yes | mandatory | yes recv | no | mandatory | no Since B asked for confirmation about the "send" connectivity (from A's point of view), A now sends an UPDATE (5) to B to confirm the connectivity from A to B: m=audio 20000 RTP/AVP 0 96 a=rtpmap:96 no-op/8000 c=IN IP4 192.0.2.1 a=curr:conn e2e send a=des:conn mandatory e2e sendrecv 6. Security Considerations In addition to the general security considerations for preconditions provided in RFC 3312, the following security issues, which are specific to connectivity preconditions, should be considered. Connectivity preconditions rely on mechanisms beyond SDP, e.g. TCPTCP connection establishment, RTP No-Op  or STUN ,, to establish and verify connectivity between an offerer and an answerer. An attacker that prevents those mechanism from succeeding can prevent media sessions from being established and hence it is RECOMMENDED that such mechanisms are adequately secured by message authentication and integrity protection. Also, the mechanisms SHOULD consider how to prevent denial of service attacks. Similarly, an attacker that can forge packets for these mechanisms can enable sessions to be established when there in fact is no media connectivity, which may lead to a poor user experience. Authentication and integrity protection of such mechanisms can prevent this type of attacks and hence use of it is RECOMMENDED. It is also strongly RECOMMENDED that integrity protection be applied to the SDP session descriptions. S/MIME  is the natural choice to provide such end-to-end integrity protection, as described in RFC 3261 . 7. IANA Considerations IANA is hereby requested to register a RFC 3312 precondition type called "conn" with the name "Connectivity precondition". The reference for this precondition type is the current document. 8. References 8.18.1. Normative References  Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.  Handley, M. and V. Jacobson, "SDP: Session Description Protocol", RFC 2327, April 1998.  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.  Camarillo, G., Marshall, W., and J. Rosenberg, "Integration of Resource Management and Session Initiation Protocol (SIP)", RFC 3312, October 2002.  Peterson, J., "S/MIME Advanced Encryption Standard (AES) Requirement for the Session Initiation Protocol (SIP)", RFC 3853, July 2004.  Camarillo, G. and P. Kyzivat, "Update to the Session Initiation Protocol (SIP) Preconditions Framework", RFC 4032, March 2005. 8.2 Rosenberg, J., "Interactive Connectivity Establishment (ICE): A Methodology for Network Address Translator (NAT) Traversal for Offer/Answer Protocols", draft-ietf-mmusic-ice-05 (work in progress), July 2005. 8.2. Informative References  Postel, J., "Transmission Control Protocol", STD 7, RFC 793, September 1981.  Stone, J., Stewart, R., and D. Otis, "Stream Control Transmission Protocol (SCTP) Checksum Change", RFC 3309, September 2002.  Rosenberg, J., Weinberger, J., Huitema, C., and R. Mahy, "STUN - Simple Traversal of User Datagram Protocol (UDP) Through Network Address Translators (NATs)", RFC 3489, March 2003.  Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video Conferences with Minimal Control", STD 65, RFC 3551, July 2003.  Yon, D. and G. Camarillo, "TCP-Based Media Transport in the Session Description Protocol (SDP)", RFC 4145, September 2005.  Andreasen, F., "RTP"A No-Op Payload Format", draft-wing-avt-rtp-noop-01 (work in progress), October 2004.  Rosenberg, J., "Interactive Connectivity Establishment (ICE): A Methodology for Network Address Translator (NAT) TraversalFormat for Multimedia Session Establishment Protocols", draft-ietf-mmusic-ice-04RTP", draft-wing-avt-rtp-noop-03 (work in progress), FebruaryMay 2005.  Kohler, E., "Datagram Congestion Control Protocol (DCCP)", draft-ietf-dccp-spec-11 (work in progress), March 2005. Authors' Addresses Flemming Andreasen Cisco System, 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 94301 USA Email: firstname.lastname@example.org 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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