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Internet Engineering Task Force (IETF)                        C. PerkinsRequest for Comments: 5762                         University of GlasgowCategory: Standards Track                                     April 2010ISSN: 2070-1721RTP and the Datagram Congestion Control Protocol (DCCP)Abstract   The Real-time Transport Protocol (RTP) is a widely used transport for   real-time multimedia on IP networks.  The Datagram Congestion Control   Protocol (DCCP) is a transport protocol that provides desirable   services for real-time applications.  This memo specifies a mapping   of RTP onto DCCP, along with associated signalling, such that real-   time applications can make use of the services provided by DCCP.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 inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc5762.Copyright Notice   Copyright (c) 2010 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Perkins                      Standards Track                    [Page 1]

RFC 5762                      RTP over DCCP                   April 2010   This document may contain material from IETF Documents or IETF   Contributions published or made publicly available before November   10, 2008.  The person(s) controlling the copyright in some of this   material may not have granted the IETF Trust the right to allow   modifications of such material outside the IETF Standards Process.   Without obtaining an adequate license from the person(s) controlling   the copyright in such materials, this document may not be modified   outside the IETF Standards Process, and derivative works of it may   not be created outside the IETF Standards Process, except to format   it for publication as an RFC or to translate it into languages other   than English.Table of Contents1. Introduction ....................................................32. Rationale .......................................................33. Conventions Used in This Memo ...................................44. RTP over DCCP: Framing ..........................................44.1. RTP Data Packets ...........................................44.2. RTP Control Packets ........................................54.3. Multiplexing Data and Control ..............................74.4. RTP Sessions and DCCP Connections ..........................74.5. RTP Profiles ...............................................85. RTP over DCCP: Signalling using SDP .............................85.1. Protocol Identification ....................................85.2. Service Codes .............................................105.3. Connection Management .....................................115.4. Multiplexing Data and Control .............................115.5. Example ...................................................116. Security Considerations ........................................127. IANA Considerations ............................................138. Acknowledgements ...............................................149. References .....................................................149.1. Normative References ......................................149.2. Informative References ....................................15Perkins                      Standards Track                    [Page 2]

RFC 5762                      RTP over DCCP                   April 20101.  Introduction   The Real-time Transport Protocol (RTP) [1] is widely used in video   streaming, telephony, and other real-time networked applications.   RTP can run over a range of lower-layer transport protocols, and the   performance of an application using RTP is heavily influenced by the   choice of lower-layer transport.  The Datagram Congestion Control   Protocol (DCCP) [2] is a transport protocol that provides desirable   properties for real-time applications running on unmanaged best-   effort IP networks.  This memo describes how RTP can be framed for   transport using DCCP, and discusses some of the implications of such   a framing.  It also describes how the Session Description Protocol   (SDP) [3] can be used to signal such sessions.   The remainder of this memo is structured as follows: it begins with a   rationale for the work inSection 2, describing why a mapping of RTP   onto DCCP is needed.  Following a description of the conventions used   in this memo inSection 3, the specification begins inSection 4 with   the definition of how RTP packets are framed within DCCP.  Associated   signalling is described inSection 5.  Security considerations are   discussed inSection 6, and IANA considerations inSection 7.2.  Rationale   With the widespread adoption of RTP have come concerns that many   real-time applications do not implement congestion control, leading   to the potential for congestion collapse of the network [15].  The   designers of RTP recognised this issue, stating inRFC 3551 that [4]:      If best-effort service is being used, RTP receivers SHOULD monitor      packet loss to ensure that the packet loss rate is within      acceptable parameters.  Packet loss is considered acceptable if a      TCP flow across the same network path and experiencing the same      network conditions would achieve an average throughput, measured      on a reasonable timescale, that is not less than the RTP flow is      achieving.  This condition can be satisfied by implementing      congestion control mechanisms to adapt the transmission rate (or      the number of layers subscribed for a layered multicast session),      or by arranging for a receiver to leave the session if the loss      rate is unacceptably high.   While the goals are clear, the development of TCP friendly congestion   control that can be used with RTP and real-time media applications is   an open research question with many proposals for new algorithms, but   little deployment experience.Perkins                      Standards Track                    [Page 3]

RFC 5762                      RTP over DCCP                   April 2010   Two approaches have been used to provide congestion control for RTP:   1) develop RTP extensions that incorporate congestion control; and 2)   provide mechanisms for running RTP over congestion-controlled   transport protocols.  An example of the first approach can be found   in [16], extending RTP to incorporate feedback information such that   TCP Friendly Rate Control (TFRC) [17] can be implemented at the   application level.  This will allow congestion control to be added to   existing applications without operating system or network support,   and it offers the flexibility to experiment with new congestion   control algorithms as they are developed.  Unfortunately, it also   passes the complexity of implementing congestion control onto   application authors, a burden which many would prefer to avoid.   The second approach is to run RTP on a lower-layer transport protocol   that provides congestion control.  One possibility is to run RTP over   TCP, as defined in [5], but the reliable nature of TCP and the   dynamics of its congestion control algorithm make this inappropriate   for most interactive real-time applications (the Stream Control   Transmission Protocol (SCTP) is inappropriate for similar reasons).   A better fit for such applications may be to run RTP over DCCP, since   DCCP offers unreliable packet delivery and a choice of congestion   control.  This gives applications the ability to tailor the transport   to their needs, taking advantage of better congestion control   algorithms as they come available, while passing the complexity of   implementation to the operating system.  If DCCP should come to be   widely available, it is believed these will be compelling advantages.   Accordingly, this memo defines a mapping of RTP onto DCCP.3.  Conventions Used in This Memo   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 inRFC 2119 [6].4.  RTP over DCCP: Framing   The following section defines how RTP and RTP Control Protocol (RTCP)   packets can be framed for transport using DCCP.  It also describes   the differences between RTP sessions and DCCP connections, and the   impact these have on the design of applications.4.1.  RTP Data Packets   Each RTP data packet MUST be conveyed in a single DCCP datagram.   Fields in the RTP header MUST be interpreted according to the RTP   specification, and any applicable RTP Profile and Payload Format.   Header processing is not affected by DCCP framing (in particular,Perkins                      Standards Track                    [Page 4]

RFC 5762                      RTP over DCCP                   April 2010   note that the semantics of the RTP sequence number and the DCCP   sequence number are not compatible, and the value of one cannot be   inferred from the other).   A DCCP connection is opened when an end system joins an RTP session,   and it remains open for the duration of the session.  To ensure NAT   bindings are kept open, an end system SHOULD send a zero-length DCCP-   Data packet once every 15 seconds during periods when it has no other   data to send.  This removes the need for RTP no-op packets [18], and   similar application-level keepalives, when using RTP over DCCP.  This   application-level keepalive does not need to be sent if it is known   that the DCCP CCID in use provides a transport-level keepalive, or if   the application can determine that there are no NAT devices on the   path.   RTP data packets MUST obey the dictates of DCCP congestion control.   In some cases, the congestion control will require a sender to send   at a rate below that which the payload format would otherwise use.   To support this, an application could use either a rate-adaptive   payload format, or a range of payload formats (allowing it to switch   to a lower rate format if necessary).  Details of the rate adaptation   policy for particular payload formats are outside the scope of this   memo (but see [19] and [20] for guidance).   RTP extensions that provide application-level congestion control   (e.g., [16]) will conflict with DCCP congestion control, and MUST NOT   be used.   DCCP allows an application to choose the checksum coverage, using a   partial checksum to allow an application to receive packets with   corrupt payloads.  Some RTP Payload Formats (e.g., [21]) can make use   of this feature in conjunction with payload-specific mechanisms to   improve performance when operating in environments with frequent non-   congestive packet corruption.  If such a payload format is used, an   RTP end system MAY enable partial checksums at the DCCP layer, in   which case the checksum MUST cover at least the DCCP and RTP headers   to ensure packets are correctly delivered.  Partial checksums MUST   NOT be used unless supported by mechanisms in the RTP payload format.4.2.  RTP Control Packets   The RTP Control Protocol (RTCP) is used in the standard manner with   DCCP.  RTCP packets are grouped into compound packets, as described   in Section 6.1 of [1], and each compound RTCP packet is transported   in a single DCCP datagram.Perkins                      Standards Track                    [Page 5]

RFC 5762                      RTP over DCCP                   April 2010   The usual RTCP timing rules apply, with the additional constraint   that RTCP packets MUST obey the DCCP congestion control algorithm   negotiated for the connection.  This can prevent a participant from   sending an RTCP packet at the expiration of the RTCP transmission   timer if there is insufficient network capacity available.  In such   cases the RTCP packet is delayed and sent at the earliest possible   instant when capacity becomes available.  The actual time the RTCP   packet was sent is then used as the basis for calculating the next   RTCP transmission time.   RTCP packets comprise only a small fraction of the total traffic in   an RTP session.  Accordingly, it is expected that delays in their   transmission due to congestion control will not be common, provided   the configured nominal "session bandwidth" (see Section 6.2 of [1])   is in line with the bandwidth achievable on the DCCP connection.  If,   however, the capacity of the DCCP connection is significantly below   the nominal session bandwidth, RTCP packets may be delayed enough for   participants to time out due to apparent inactivity.  In such cases,   the session parameters SHOULD be re-negotiated to more closely match   the available capacity, for example by performing a re-invite with an   updated "b=" line when using the Session Initiation Protocol [22] for   signalling.      Note: Since the nominal session bandwidth is chosen based on media      codec capabilities, a session where the nominal bandwidth is much      larger than the available bandwidth will likely become unusable      due to constraints on the media channel, and so require      negotiation of a lower bandwidth codec, before it becomes unusable      due to constraints on the RTCP channel.   As noted in Section 17.1 of [2], there is the potential for overlap   between information conveyed in RTCP packets and that conveyed in   DCCP acknowledgement options.  In general this is not an issue since   RTCP packets contain media-specific data that is not present in DCCP   acknowledgement options, and DCCP options contain network-level data   that is not present in RTCP.  Indeed, there is no overlap between the   five RTCP packet types defined in the RTP specification [1] and the   standard DCCP options [2].  There are, however, cases where overlap   does occur: most clearly between the Loss RLE Report Blocks defined   as part of the RTCP Extended Reports [23] and the DCCP Ack Vector   option.  If there is overlap between RTCP report packets and DCCP   acknowledgements, an application SHOULD use either RTCP feedback or   DCCP acknowledgements, but not both (use of both types of feedback   will waste available network capacity, but is not otherwise harmful).Perkins                      Standards Track                    [Page 6]

RFC 5762                      RTP over DCCP                   April 20104.3.  Multiplexing Data and Control   The obvious mapping of RTP onto DCCP creates two DCCP connections for   each RTP flow: one for RTP data packets and one for RTP control   packets.  A frequent criticism of RTP relates to the number of ports   it uses, since large telephony gateways can support more than 32768   RTP flows between pairs of gateways, and so run out of UDP ports.  In   addition, use of multiple ports complicates NAT traversal.  For these   reasons, it is RECOMMENDED that the RTP and RTCP traffic for a single   RTP session is multiplexed onto a single DCCP connection following   the guidelines in [7], where possible (it may not be possible in all   circumstances, for example when translating from an RTP stream over a   non-DCCP transport that uses conflicting RTP payload types and RTCP   packet types).4.4.  RTP Sessions and DCCP Connections   An end system SHOULD NOT assume that it will observe only a single   RTP synchronisation source (SSRC) because it is using DCCP framing.   An RTP session can span any number of transport connections, and can   include RTP mixers or translators bringing other participants into   the session.  The use of a unicast DCCP connection does not imply   that the RTP session will have only two participants, and RTP end   systems SHOULD assume that multiple synchronisation sources may be   observed when using RTP over DCCP, unless otherwise signalled.   An RTP translator bridging multiple DCCP connections to form a single   RTP session needs to be aware of the congestion state of each DCCP   connection, and must adapt the media to the available capacity of   each.  The Codec Control Messages defined in [24] may be used to   signal congestion state to the media senders, allowing them to adapt   their transmission.  Alternatively, media transcoding may be used to   perform adaptation: this is computationally expensive, induces delay,   and generally gives poor-quality results.  Depending on the payload,   it might also be possible to use some form of scalable coding.   A single RTP session may also span a DCCP connection and some other   type of transport connection.  An example might be an RTP over DCCP   connection from an RTP end system to an RTP translator, with an RTP   over UDP/IP multicast group on the other side of the translator.  A   second example might be an RTP over DCCP connection that links Public   Switched Telephone Network (PSTN) gateways.  The issues for such an   RTP translator are similar to those when linking two DCCP   connections, except that the congestion control algorithms on either   side of the translator may not be compatible.  Implementation of   effective translators for such an environment is non-trivial.Perkins                      Standards Track                    [Page 7]

RFC 5762                      RTP over DCCP                   April 20104.5.  RTP Profiles   In general, there is no conflict between new RTP profiles and DCCP   framing, and most RTP profiles can be negotiated for use over DCCP   with the following exceptions:   o  An RTP profile that is intolerant of packet corruption may      conflict with the DCCP partial checksum feature.  An example of      this is the integrity protection provided by the RTP/SAVP profile,      which cannot be used in conjunction with DCCP partial checksums.   o  An RTP profile that mandates a particular non-DCCP lower-layer      transport will conflict with DCCP.   RTP profiles that fall under these exceptions SHOULD NOT be used with   DCCP unless the conflicting features can be disabled.   Of the profiles currently defined, the RTP Profile for Audio and   Video Conferences with Minimal Control [4], the Secure Real-time   Transport Protocol [8], the Extended RTP Profile for RTCP-based   Feedback [9], and the Extended Secure RTP Profile for RTCP-based   Feedback [10] MAY be used with DCCP (noting the potential conflict   between DCCP partial checksums and the integrity protection provided   by the secure RTP variants -- seeSection 6).5.  RTP over DCCP: Signalling using SDP   The Session Description Protocol (SDP) [3] and the offer/answer model   [11] are widely used to negotiate RTP sessions (for example, using   the Session Initiation Protocol [22]).  This section describes how   SDP is used to signal RTP sessions running over DCCP.5.1.  Protocol Identification   SDP uses a media ("m=") line to convey details of the media format   and transport protocol used.  The ABNF syntax of a media line is as   follows (from [3]):       media-field = %x6d "=" media SP port ["/" integer] SP proto                     1*(SP fmt) CRLF   The proto field denotes the transport protocol used for the media,   while the port indicates the transport port to which the media is   sent.  Following [5] and [12], this memo defines these five values of   the proto field to indicate media transported using DCCP:Perkins                      Standards Track                    [Page 8]

RFC 5762                      RTP over DCCP                   April 2010       DCCP       DCCP/RTP/AVP       DCCP/RTP/SAVP       DCCP/RTP/AVPF       DCCP/RTP/SAVPF   The "DCCP" protocol identifier is similar to the "UDP" and "TCP"   protocol identifiers and denotes the DCCP transport protocol [2], but   not its upper-layer protocol.  An SDP "m=" line that specifies the   "DCCP" protocol MUST further qualify the application-layer protocol   using a "fmt" identifier (the "fmt" namespace is managed in the same   manner as for the "UDP" protocol identifier).  A single DCCP port is   used, as denoted by the port field in the media line.  The "DCCP"   protocol identifier MUST NOT be used to signal RTP sessions running   over DCCP; those sessions MUST use a protocol identifier of the form   "DCCP/RTP/..." as described below.   The "DCCP/RTP/AVP" protocol identifier refers to RTP using the RTP   Profile for Audio and Video Conferences with Minimal Control [4]   running over DCCP.   The "DCCP/RTP/SAVP" protocol identifier refers to RTP using the   Secure Real-time Transport Protocol [8] running over DCCP.   The "DCCP/RTP/AVPF" protocol identifier refers to RTP using the   Extended RTP Profile for RTCP-based Feedback [9] running over DCCP.   The "DCCP/RTP/SAVPF" protocol identifier refers to RTP using the   Extended Secure RTP Profile for RTCP-based Feedback [10] running over   DCCP.   RTP payload formats used with the "DCCP/RTP/AVP", "DCCP/RTP/SAVP",   "DCCP/RTP/AVPF", and "DCCP/RTP/SAVPF" protocol identifiers MUST use   the payload type number as their "fmt" value.  If the payload type   number is dynamically assigned, an additional "rtpmap" attribute MUST   be included to specify the format name and parameters as defined by   the media type registration for the payload format.   DCCP port 5004 is registered for use by the RTP profiles listed   above, and SHOULD be the default port chosen by applications using   those profiles.  If multiple RTP sessions are active from a host,   even-numbered ports in the dynamic range SHOULD be used for the other   sessions.  If RTCP is to be sent on a separate DCCP connection to   RTP, the RTCP connection SHOULD use the next higher destination port   number, unless an alternative DCCP port is signalled using the   "a=rtcp:" attribute [13].  For improved interoperability, "a=rtcp:"   SHOULD be used whenever an alternate DCCP port is used.Perkins                      Standards Track                    [Page 9]

RFC 5762                      RTP over DCCP                   April 20105.2.  Service Codes   In addition to the port number, specified on the SDP "m=" line, a   DCCP connection has an associated service code.  A single new SDP   attribute ("dccp-service-code") is defined to signal the DCCP service   code according to the following ABNF [14]:       dccp-service-attr = %x61 "=dccp-service-code:" service-code       service-code      = hex-sc / decimal-sc / ascii-sc       hex-sc            = %x53 %x43 "=" %x78 *HEXDIG       decimal-sc        = %x53 %x43 "="  *DIGIT       ascii-sc          = %x53 %x43 ":"  *sc-char       sc-char           = %d42-43 / %d45-47 / %d63-90 / %d95 / %d97-122   where DIGIT and HEXDIG are as defined in [14].  The service code is   interpreted as defined in Section 8.1.2 of [2] and may be specified   using either the hexadecimal, decimal, or ASCII formats.  A parser   MUST interpret service codes according to their numeric value,   independent of the format used to represent them in SDP.   The following DCCP service codes are registered for use with RTP:   o  SC:RTPA (equivalently SC=1381257281 or SC=x52545041): an RTP      session conveying audio data (and OPTIONAL multiplexed RTCP)   o  SC:RTPV (equivalently SC=1381257302 or SC=x52545056): an RTP      session conveying video data (and OPTIONAL multiplexed RTCP)   o  SC:RTPT (equivalently SC=1381257300 or SC=x52545054): an RTP      session conveying text media (and OPTIONAL multiplexed RTCP)   o  SC:RTPO (equivalently SC=1381257295 or SC=x5254504f): an RTP      session conveying any other type of media (and OPTIONAL      multiplexed RTCP)   o  SC:RTCP (equivalently SC=1381253968 or SC=x52544350): an RTCP      connection, separate from the corresponding RTP   To ease the job of middleboxes, applications SHOULD use these service   codes to identify RTP sessions running within DCCP.  The service code   SHOULD match the top-level media type signalled for the sessionPerkins                      Standards Track                   [Page 10]

RFC 5762                      RTP over DCCP                   April 2010   (i.e., the SDP "m=" line), with the exception connections using media   types other than audio, video, or text, which use SC:RTPO, and   connections that transport only RTCP packets, which use SC:RTCP.   The "a=dccp-service-code:" attribute is a media-level attribute that   is not subject to the charset attribute.5.3.  Connection Management   The "a=setup:" attribute indicates which of the endpoints should   initiate the DCCP connection establishment (i.e., send the initial   DCCP-Request packet).  The "a=setup:" attribute MUST be used in a   manner comparable with [12], except that DCCP connections are being   initiated rather than TCP connections.   After the initial offer/answer exchange, the endpoints may decide to   re-negotiate various parameters.  The "a=connection:" attribute MUST   be used in a manner compatible with [12] to decide whether a new DCCP   connection needs to be established as a result of subsequent offer/   answer exchanges, or if the existing connection should still be used.5.4.  Multiplexing Data and Control   A single DCCP connection can be used to transport multiplexed RTP and   RTCP packets.  Such multiplexing MUST be signalled using an "a=rtcp-   mux" attribute according to [7].  If multiplexed RTP and RTCP are not   to be used, then the "a=rtcp-mux" attribute MUST NOT be present in   the SDP offer, and a separate DCCP connection MUST be opened to   transport the RTCP data on a different DCCP port.5.5.  Example   An offerer at 192.0.2.47 signals its availability for an H.261 video   session, using RTP/AVP over DCCP with service code "RTPV" (using the   hexadecimal encoding of the service code in the SDP).  RTP and RTCP   packets are multiplexed onto a single DCCP connection:       v=0       o=alice 1129377363 1 IN IP4 192.0.2.47       s=-       c=IN IP4 192.0.2.47       t=0 0       m=video 5004 DCCP/RTP/AVP 99       a=rtcp-mux       a=rtpmap:99 h261/90000       a=dccp-service-code:SC=x52545056       a=setup:passive       a=connection:newPerkins                      Standards Track                   [Page 11]

RFC 5762                      RTP over DCCP                   April 2010   An answerer at 192.0.2.128 receives this offer and responds with the   following answer:       v=0       o=bob 1129377364 1 IN IP4 192.0.2.128       s=-       c=IN IP4 192.0.2.128       t=0 0       m=video 9 DCCP/RTP/AVP 99       a=rtcp-mux       a=rtpmap:99 h261/90000       a=dccp-service-code:SC:RTPV       a=setup:active       a=connection:new   The end point at 192.0.2.128 then initiates a DCCP connection to port   5004 at 192.0.2.47.  DCCP port 5004 is used for both the RTP and RTCP   data, and port 5005 is unused.  The textual encoding of the service   code is used in the answer, and represents the same service code as   in the offer.6.  Security Considerations   The security considerations in the RTP specification [1] and any   applicable RTP profile (e.g., [4], [8], [9], or [10]) or payload   format apply when transporting RTP over DCCP.   The security considerations in the DCCP specification [2] apply.   The SDP signalling described inSection 5 is subject to the security   considerations of [3], [11], [12], [5], and [7].   The provision of effective congestion control for RTP through use of   DCCP is expected to help reduce the potential for denial of service   present when RTP flows ignore the advice in [1] to monitor packet   loss and reduce their sending rate in the face of persistent   congestion.   There is a potential conflict between the Secure RTP profiles ([8],   [10]) and the DCCP partial checksum option, since these profiles   introduce, and recommend the use of, message authentication for RTP   and RTCP packets.  Message authentication codes of the type used by   these profiles cannot be used with partial checksums, since any bit   error in the DCCP packet payload will cause the authentication check   to fail.  Accordingly, DCCP partial checksums SHOULD NOT be used in   conjunction with Secure Real-time Transport Protocol (SRTP)   authentication.  The confidentiality features of the basic RTP   specification cannot be used with DCCP partial checksums, since bitPerkins                      Standards Track                   [Page 12]

RFC 5762                      RTP over DCCP                   April 2010   errors propagate.  Also, despite the fact that bit errors do not   propagate when using AES in counter mode, the Secure RTP profiles   SHOULD NOT be used with DCCP partial checksums, since the profiles   require authentication for security, and authentication is   incompatible with partial checksums.7.  IANA Considerations   The following SDP "proto" field identifiers have been registered (seeSection 5.1):      Type          SDP Name                                Reference      ----          --------                                ---------      proto         DCCP                                    [RFC5762]                    DCCP/RTP/AVP                            [RFC5762]                    DCCP/RTP/SAVP                           [RFC5762]                    DCCP/RTP/AVPF                           [RFC5762]                    DCCP/RTP/SAVPF                          [RFC5762]   The following new SDP attribute ("att-field") has been registered:      Contact name: Colin Perkins <csp@csperkins.org>      Attribute name: dccp-service-code      Long-form attribute name in English: DCCP service code      Type of attribute: Media level.      Subject to the charset attribute?  No.      Purpose of the attribute: seeRFC 5762, Section 5.2      Allowed attribute values: seeRFC 5762, Section 5.2   The following DCCP service code values have been registered (seeSection 5.2):      1381257281    RTPA    RTP session conveying audio     [RFC5762]                             data (and associated RTCP)      1381257302    RTPV    RTP session conveying video     [RFC5762]                             data (and associated RTCP)      1381257300    RTPT    RTP session conveying text      [RFC5762]                             media (and associated RTCP)      1381257295    RTPO    RTP session conveying other     [RFC5762]                             media (and associated RTCP)      1381253968    RTCP    RTCP connection, separate from  [RFC5762]                             the corresponding RTPPerkins                      Standards Track                   [Page 13]

RFC 5762                      RTP over DCCP                   April 2010   The following DCCP ports have been registered (seeSection 5.1):      avt-profile-1 5004/dccp  RTP media data       [RFC3551,RFC5762]      avt-profile-2 5005/dccp  RTP control protocol [RFC3551,RFC5762]   Note: ports 5004/tcp, 5004/udp, 5005/tcp, and 5005/udp have existing   registrations, but incorrect descriptions and references.  The IANA   has updated the existing registrations as follows:      avt-profile-1 5004/tcp   RTP media data       [RFC3551,RFC4571]      avt-profile-1 5004/udp   RTP media data       [RFC3551]      avt-profile-2 5005/tcp   RTP control protocol [RFC3551,RFC4571]      avt-profile-2 5005/udp   RTP control protocol [RFC3551]8.  Acknowledgements   This work was supported in part by the UK Engineering and Physical   Sciences Research Council.  Thanks are due to Philippe Gentric,   Magnus Westerlund, Sally Floyd, Dan Wing, Gorry Fairhurst, Stephane   Bortzmeyer, Arjuna Sathiaseelan, Tom Phelan, Lars Eggert, Eddie   Kohler, Miguel Garcia, and the other members of the DCCP working   group for their comments.9.  References9.1.  Normative References   [1]   Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson,         "RTP: A Transport Protocol for Real-Time Applications", STD 64,RFC 3550, July 2003.   [2]   Kohler, E., Handley, M., and S. Floyd, "Datagram Congestion         Control Protocol (DCCP)",RFC 4340, March 2006.   [3]   Handley, M., Jacobson, V., and C. Perkins, "SDP: Session         Description Protocol",RFC 4566, July 2006.   [4]   Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video         Conferences with Minimal Control", STD 65,RFC 3551, July 2003.   [5]   Lazzaro, J., "Framing Real-time Transport Protocol (RTP) and         RTP Control Protocol (RTCP) Packets over Connection-Oriented         Transport",RFC 4571, July 2006.   [6]   Bradner, S., "Key words for use in RFCs to Indicate Requirement         Levels",BCP 14,RFC 2119, March 1997.Perkins                      Standards Track                   [Page 14]

RFC 5762                      RTP over DCCP                   April 2010   [7]   Perkins, C. and M. Westerlund, "Multiplexing RTP Data and         Control Packets on a Single Port",RFC 5761, April 2010.   [8]   Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.         Norrman, "The Secure Real-time Transport Protocol (SRTP)",RFC 3711, March 2004.   [9]   Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,         "Extended RTP Profile for Real-time Transport Control Protocol         (RTCP)-Based Feedback (RTP/AVPF)",RFC 4585, July 2006.   [10]  Ott, J. and E. Carrara, "Extended Secure RTP Profile for Real-         time Transport Control Protocol (RTCP)-Based Feedback (RTP/         SAVPF)",RFC 5124, February 2008.   [11]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with         Session Description Protocol (SDP)",RFC 3264, June 2002.   [12]  Yon, D. and G. Camarillo, "TCP-Based Media Transport in the         Session Description Protocol (SDP)",RFC 4145, September 2005.   [13]  Huitema, C., "Real Time Control Protocol (RTCP) attribute in         Session Description Protocol (SDP)",RFC 3605, October 2003.   [14]  Crocker, D. and P. Overell, "Augmented BNF for Syntax         Specifications: ABNF", STD 68,RFC 5234, January 2008.9.2.  Informative References   [15]  Floyd, S. and J. Kempf, "IAB Concerns Regarding Congestion         Control for Voice Traffic in the Internet",RFC 3714,         March 2004.   [16]  Gharai, L.,"RTP with TCP Friendly Rate Control", Work         in Progress, July 2007.   [17]  Floyd, S., Handley, M., Padhye, J., and J. Widmer, "TCP         Friendly Rate Control (TFRC): Protocol Specification",RFC 5348, September 2008.   [18]  Andreasen, F., Oran, D., and D. Wing, "A No-Op Payload Format         for RTP", Work in Progress, May 2005.   [19]  Phelan, T., "Strategies for Streaming Media Applications Using         TCP-Friendly Rate  Control", Work in Progress, July 2007.   [20]  Phelan, T., "Datagram Congestion Control Protocol (DCCP) User         Guide", Work in Progress, April 2005.Perkins                      Standards Track                   [Page 15]

RFC 5762                      RTP over DCCP                   April 2010   [21]  Sjoberg, J., Westerlund, M., Lakaniemi, A., and Q. Xie, "RTP         Payload Format and File Storage Format for the Adaptive Multi-         Rate (AMR) and Adaptive Multi-Rate Wideband (AMR-WB) Audio         Codecs",RFC 4867, April 2007.   [22]  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.   [23]  Friedman, T., Caceres, R., and A. Clark, "RTP Control Protocol         Extended Reports (RTCP XR)",RFC 3611, November 2003.   [24]  Wenger, S., Chandra, U., Westerlund, M., and B. Burman, "Codec         Control Messages in the RTP Audio-Visual Profile with Feedback         (AVPF)", Work in Progress, October 2007.Author's Address   Colin Perkins   University of Glasgow   Department of Computing Science   Glasgow  G12 8QQ   UK   EMail: csp@csperkins.orgPerkins                      Standards Track                   [Page 16]