1、 International Telecommunication Union ITU-T H.248.82TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (03/2013) SERIES H: AUDIOVISUAL AND MULTIMEDIA SYSTEMSInfrastructure of audiovisual services Communication procedures Gateway control protocol: Explicit congestion notification support Recommendation
2、 ITU-T H.248.82 ITU-T H-SERIES RECOMMENDATIONS AUDIOVISUAL AND MULTIMEDIA SYSTEMS CHARACTERISTICS OF VISUAL TELEPHONE SYSTEMS H.100H.199 INFRASTRUCTURE OF AUDIOVISUAL SERVICES General H.200H.219 Transmission multiplexing and synchronization H.220H.229 Systems aspects H.230H.239 Communication procedu
3、res H.240H.259Coding of moving video H.260H.279 Related systems aspects H.280H.299 Systems and terminal equipment for audiovisual services H.300H.349 Directory services architecture for audiovisual and multimedia services H.350H.359 Quality of service architecture for audiovisual and multimedia serv
4、ices H.360H.369 Supplementary services for multimedia H.450H.499 MOBILITY AND COLLABORATION PROCEDURES Overview of Mobility and Collaboration, definitions, protocols and procedures H.500H.509 Mobility for H-Series multimedia systems and services H.510H.519 Mobile multimedia collaboration application
5、s and services H.520H.529 Security for mobile multimedia systems and services H.530H.539 Security for mobile multimedia collaboration applications and services H.540H.549 Mobility interworking procedures H.550H.559 Mobile multimedia collaboration inter-working procedures H.560H.569 BROADBAND, TRIPLE
6、-PLAY AND ADVANCED MULTIMEDIA SERVICES Broadband multimedia services over VDSL H.610H.619 Advanced multimedia services and applications H.620H.629 Ubiquitous sensor network applications and Internet of Things H.640H.649 IPTV MULTIMEDIA SERVICES AND APPLICATIONS FOR IPTV General aspects H.700H.719 IP
7、TV terminal devices H.720H.729 IPTV middleware H.730H.739 IPTV application event handling H.740H.749 IPTV metadata H.750H.759 IPTV multimedia application frameworks H.760H.769 IPTV service discovery up to consumption H.770H.779 Digital Signage H.780H.789 For further details, please refer to the list
8、 of ITU-T Recommendations. Rec. ITU-T H.248.82 (03/2013) i Recommendation ITU-T H.248.82 Gateway control protocol: Explicit congestion notification support Summary Recommendation ITU-T H.248.82 defines a package to allow ITU-T H.248 controlled media gateways to support explicit congestion notificati
9、on (ECN). ECN is a mechanism to provide indications of incipient congestion affecting a Real-Time Protocol (RTP) stream to a receiver and, usually, to a sender. ECN when used with an RTP stream over UDP uses the RTP control protocol to provide feedback of ECN congestion markings to an RTP sender. Th
10、e mechanism allows senders and/or receivers to react in order to reduce congestion in real-time communications. This Recommendation only describes the use of ECN in RTP over UDP streams. History Edition Recommendation Approval Study Group 1.0 ITU-T H.248.82 2013-03-16 16 ii Rec. ITU-T H.248.82 (03/2
11、013) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for
12、 studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study
13、 groups which, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis w
14、ith ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory pro
15、visions (to ensure, e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of
16、 such words does not suggest that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no pos
17、ition concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, prot
18、ected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2013 All rights reserved. No part
19、of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU-T H.248.82 (03/2013) iii Table of Contents Page 1 Scope 1 2 References. 1 3 Definitions 2 3.1 Terms defined elsewhere 2 3.2 Terms defined in this Recommendation . 2 4 Abbreviations a
20、nd acronyms 2 5 Conventions 3 6 Use of ECN with ITU-T H.248 3 6.1 Basic ECN control loop 3 6.2 Use of ECN with TCP traffic . 4 6.3 Use of ECN with RTP-over-UDP traffic 5 6.4 Capability declaration and negotiation of ECN in the control plane 7 6.5 ECN interworking scenarios . 8 7 ECN for RTP-over-UDP
21、 Support package . 10 7.1 Properties 10 7.2 Events . 14 7.3 Signals 14 7.4 Statistics 15 7.5 Error codes 17 7.6 Procedures 17 Rec. ITU-T H.248.82 (03/2013) 1 Recommendation ITU-T H.248.82 Gateway control protocol: Explicit congestion notification support 1 Scope Explicit congestion notification is a
22、 mechanism to provide indications of incipient congestion affecting an RTP stream to a receiver and, usually, to a sender. ECN, when used with an RTP stream over UDP, uses the RTP control protocol to provide feedback of ECN congestion markings to an RTP sender. Depending on previous signalling the s
23、ender and/or receiver can take action to minimize congestion in reception of the ECN congestion markings. The session description protocol (SDP) is utilized to indicate support of ECN and what parameters relate to its use. As a media gateway (MG) sends/receives RTP based media (and RTCP), these para
24、meters must be agreed and coordinated between the media gateway controller (MGC) and the MG. In ITU-T H.248 controlled gateways, this information must be provided via ITU-T H.248. This Recommendation defines the “ECN for RTP-over-UDP Support Package“ in order to establish ECN support on media gatewa
25、ys. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to rev
26、ision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within thi
27、s Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T E.107 Recommendation ITU-T E.107 (2007), Emergency Telecommunications Service (ETS) and interconnection framework for national implementations of ETS. ITU-T H.248.1 Recommendation ITU-T H.248.1 (2013)
28、, Gateway Control Protocol: Version 3. ITU-T H.248.47 Recommendation ITU-T H.248.47 (2008), Gateway Control Protocol: Statistic conditional reporting package. ITU-T H.248.50 Recommendation ITU-T H.248.50 (2010), Gateway Control Protocol: NAT traversal toolkit packages. ITU-T H.248.64 Recommendation
29、ITU-T H.248.64 (2013), Gateway Control Protocol: IP router packages. ITU-T H.248.81 Recommendation ITU-T H.248.81 (2011), Gateway Control Protocol: Guidelines on the use of the international emergency preference scheme (IEPS) call indicator and priority indicator in ITU-T H.248 profiles. IETF RFC 31
30、68 IETF RFC 3168 (2001), The Addition of Explicit Congestion Notification (ECN) to IP. IETF RFC 3550 IETF RFC 3550 (2003), RTP: A Transport Protocol for Real-Time Applications. IETF RFC 3611 IETF RFC 3611 (2003), RTP Control Protocol Extended Reports (RTCP XR). 2 Rec. ITU-T H.248.82 (03/2013) IETF R
31、FC 4585 IETF RFC 4585 (2006), Extended RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/AVPF). IETF RFC 5245 IETF RFC 5245 (2010), Interactive Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT) Traversal for Offer/Answer Protocols. IETF R
32、FC 5506 IETF RFC 5506 (2009), Support for Reduced-Size Real-Time Transport Control Protocol (RTCP): Opportunities and Consequences. IETF RFC 6679 IETF RFC 6679 (2012), Explicit Congestion Notification (ECN) for RTP over UDP. 3 Definitions 3.1 Terms defined elsewhere This Recommendation uses the foll
33、owing terms defined elsewhere: 3.1.1 sender IETF RFC 6679: A sender of RTP packets carrying an encoded media stream. The sender can change how the media transmission is performed by varying the media coding or packetization. It is one endpoint of the ECN control loop. NOTE The sender in this sense m
34、ay or may not be the same as the RTP End System. 3.1.2 receiver IETF RFC 6679: A receiver of RTP packets with the intention to consume the media stream. It sends RTCP feedback on the received stream. It is the other end-point of the ECN control loop. NOTE The receiver in this sense may or may not be
35、 the same as the RTP End System. 3.2 Terms defined in this Recommendation This Recommendation defines the following term: 3.2.1 AuditValue.req: An ITU-T H.248.1 AuditValue command request. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: ABNF Augmented
36、Backus-Naur Form B2BIH Back-to-Back Internet protocol Host B2BRE Back-to-Back RTP End system CE Congestion Experienced DCCP Datagram Congestion Control Protocol ECN Explicit Congestion Notification ECT ECN Capable Transport ETS Emergency Telecommunications Service IP Internet Protocol IPR Internet P
37、rotocol Router LD Local Destination LS Local Source Lx Layer number Rec. ITU-T H.248.82 (03/2013) 3 MCU Media Control Unit MG Media Gateway MGC Media Gateway Controller MSRP Message Sending Relay Protocol NAT Network Address Translation RD Remote Destination RS Remote Source RTP Real Time Protocol R
38、TCP Real-Time Transport Control Protocol SCTP Stream Control Transport Protocol SDP Session Description Protocol SIP Session Initiation Protocol SSRC Synchronization Source STUN Session Traversal Utilities for NAT UDP User Datagram Protocol 5 Conventions Elements of the ITU-T H.248 protocol model, e
39、.g., Context, Termination, Stream, Event are represented using the first letter capitalized. ITU-T H.248 Property, Event, Signal and Parameter identities are given in italics. When used in the main text SDP syntax is highlighted in bold i.e., “m=“. 6 Use of ECN with ITU-T H.248 ITU-T H.248 entities
40、(MG and MGC) may be involved with ECN in multiple ways. Clause 6.1 introduces the basic control principle. Subsequent clauses illustrate example IP transport (and possibly application) protocol-specific use of ECN with ITU-T H.248. 6.1 Basic ECN control loop IETF RFC 3168 defines an addition to IP f
41、or ECN support. This support relates to a unidirectional connection model, i.e., IP traffic in IP source host to IP destination host direction. Figure 1 illustrates the basic ECN control principle. The control loop may be abstracted by four components in the user plane: 1. the congestion notificatio
42、n information flow in source to destination host direction; 2. the feedback information flow in reverse direction, back to the traffic source; 3. the actuating elements in case of indicated congestion (typically located in the source host); and 4. the sensor elements, responsible for indicating cong
43、estion (at a network route, in an IP hop) by ECN marking in the IP path. There might be a further component in the control plane for: 5. the indication and negotiation of a congestion control. 4 Rec. ITU-T H.248.82 (03/2013) H.248.82(13)_F01X-over-IPECN-capable host1) Congestion notificationvia IP h
44、eader field “ECN“IP networkas a single ECN domainIP sourcehostControl frameworkIPIP destinationhostIP Hop entitiesin theIP Media-Path( ECN markingcapability)ECN-capable host2) Feedback from receiver to sourcevia protocol X (e.g., L4 protocol e.g., TCP,DCCP, SCTP, or L4+ protocol e.g., RTCP)3a) Contr
45、ol reaction Sender-driven congestion controlvia e.g., adaptation oftransmission (bit)rate3b) Control reaction Receiver-driven congestion control(application specific)Possible ITU-T H.248 MG role as ECN-capable IP source host.ITU-T H.248 connection models, e.g.,: (IP,IP), (IP, non-IP)Possible ITU-T H
46、.248 MG role as ECN active marker (within an ECN domain), ECN remarker (between two ECN domains), ECN transparent forwarding (passive IP hop)ITU-T H.248 connection models: (IP,IP)Possible ITU-T H.248 MG role as ECN-capable IP destination host.ITU-T H.248 connection models, e.g.,: (IP,IP), (IP, non-I
47、P)Closed control loopNOTE The thick arrow shows the unidirectional IP packet path (where hop entities may provide ECN-CE marking). The thin arrow in reverse direction indicates protocol X packets in feedback direction. Figure 1 ECN supporting IP network (ITU-T H.248 bearer plane) Basic model of the
48、ECN control loop In Figure 1, the control loop spans two ECN-capable IP host entities with information flows in both directions, requiring a bidirectional communication path. There are different protocols in use for ECN (Figure 1) in each direction: IPv4 or IPv6 in the source-to-destination host dir
49、ection for carrying ECN indications; Higher layer protocols in the reverse direction. This is normally the applied IP transport protocol if extended (like TCP) or designed for ECN support (like DCCP, SCTP); or an L4+ protocol (like RTCP in case of UDP transport). ITU-T H.248 MG entities may be involved in ECN control loops in various ways. There may be potential use cases for all four of the above indicated protocol groups to be involved in the control loop. Figure 1 outlines some po
