1、 International Telecommunication Union ITU-T H.460.24TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU Amendment 1(05/2011) SERIES H: AUDIOVISUAL AND MULTIMEDIA SYSTEMSInfrastructure of audiovisual services Supplementary services for multimedia Point-to-point media through network address translators
2、and firewalls within ITU-T H.323 systemsAmendment 1: Improvements for NAT traversal without intermediary entities Recommendation ITU-T H.460.24 (2009) Amendment 1 ITU-T H-SERIES RECOMMENDATIONS AUDIOVISUAL AND MULTIMEDIA SYSTEMS CHARACTERISTICS OF VISUAL TELEPHONE SYSTEMS H.100H.199 INFRASTRUCTURE O
3、F AUDIOVISUAL SERVICES General H.200H.219 Transmission multiplexing and synchronization H.220H.229 Systems aspects H.230H.239 Communication procedures H.240H.259 Coding of moving video H.260H.279 Related systems aspects H.280H.299 Systems and terminal equipment for audiovisual services H.300H.349 Di
4、rectory services architecture for audiovisual and multimedia services H.350H.359 Quality of service architecture for audiovisual and multimedia services H.360H.369 Supplementary services for multimedia H.450H.499MOBILITY AND COLLABORATION PROCEDURES Overview of Mobility and Collaboration, definition
5、s, protocols and procedures H.500H.509 Mobility for H-Series multimedia systems and services H.510H.519 Mobile multimedia collaboration applications and services H.520H.529 Security for mobile multimedia systems and services H.530H.539 Security for mobile multimedia collaboration applications and se
6、rvices H.540H.549 Mobility interworking procedures H.550H.559 Mobile multimedia collaboration inter-working procedures H.560H.569 BROADBAND, TRIPLE-PLAY AND ADVANCED MULTIMEDIA SERVICES Broadband multimedia services over VDSL H.610H.619 Advanced multimedia services and applications H.620H.629 IPTV M
7、ULTIMEDIA SERVICES AND APPLICATIONS FOR IPTV General aspects H.700H.719 IPTV 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.77
8、9 For further details, please refer to the list of ITU-T Recommendations. Rec. ITU-T H.460.24 (2009)/Amd.1 (05/2011) i Recommendation ITU-T H.460.24 Point-to-point media through network address translators and firewalls within ITU-T H.323 systems Amendment 1 Improvements for NAT traversal without in
9、termediary entities Summary Recommendation ITU-T H.460.24 enables an ITU-T H.323 gatekeeper to formulate a decision to enable direct media flows between ITU-T H.323 endpoints that reside behind network address translator (NAT)/firewall (FW) devices. This extension is used in conjunction with Recomme
10、ndation ITU-T H.460.18 to facilitate the traversal of media across NAT/FW devices and Recommendation ITU-T H.460.23 to discover the characteristics of NAT/FW devices sitting in front of ITU-T H.323 endpoints, reducing the frequency with which media proxy devices (as described in Recommendation ITU-T
11、 H.460.19) are needed by allowing direct media connectivity between the endpoints. Connectivity is achieved via the formulation of an intelligent media transmission decision and call signalling that instructs endpoints to initiate media flows in such a manner that a reliable direct media pathway is
12、established, even if one or both endpoints reside behind a NAT/FW device. Amendment 1 to Recommendation ITU-T H.460.24 further improves conditions where media pathways do not require the services of an intermediary to achieve NAT traversal. New Annex B allows endpoints under certain conditions, afte
13、r first establishing media flows through an intermediary entity, to probe for a direct route and, if detected, change the media pathway to flow directly between the endpoints freeing up the resources of the intermediary entity. History Edition Recommendation Approval Study Group 1.0 ITU-T H.460.24 2
14、009-12-14 16 1.1 ITU-T H.460.24 (2009) Amd. 1 2011-05-14 16 ii Rec. ITU-T H.460.24 (2009)/Amd.1 (05/2011) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU T
15、elecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardizati
16、on Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study 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 technol
17、ogy which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with 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
18、 with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (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 obligat
19、ory language such as “must“ and the negative equivalents are used to express requirements. The use of 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
20、of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position 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 th
21、e date of approval of this Recommendation, ITU had not received notice of intellectual property, protected 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 co
22、nsult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2012 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU-T H.460.24 (2009)/Amd.1 (05/2011) iii Table of Contents Page 1 Scope 1 2 Referenc
23、es. 1 3 Definitions 2 3.1 Terms defined elsewhere 2 3.2 Terms defined in this Recommendation . 2 4 Abbreviations and acronyms 2 5 Feature description 3 6 Capability advertisement 3 7 Call establishment procedure 4 7.1 Gatekeeper parameters . 5 7.2 Non-NAT/FW parameters 5 7.3 NAT/FW-specific paramete
24、rs 6 8 Calculating media pathways . 7 9 Determining media strategy 8 9.1 Compatibility 9 9.2 Same NAT/FW determination 9 9.3 Must proxy media determination 9 9.4 General NAT strategy determination . 10 9.5 Example P2Pnat media calculations . 10 9.6 Reporting NAT strategy results to the endpoint . 11
25、 10 Placing the call 12 11 Special considerations 12 11.1 RTP/SRTP/RTCP/SRTCP keep-alive packet. 12 11.2 Timeouts waiting for first packet . 12 Annex A Probing for same NAT 13 A.1 Notification of direct connectivity probing 13 A.2 Procedure to probe direct connectivity . 14 A.3 Probe packet format 1
26、4 Annex B External NAT probing . 15 B.1 Background . 16 B.2 Procedure to probe for direct connectivity . 16 B.3 Probe packet format 17 B.4 Annex B ASN.1 code . 18 Rec. ITU-T H.460.24 (2009)/Amd.1 (05/2011) 1 Recommendation ITU-T H.460.24 Point-to-point media through network address translators and f
27、irewalls within ITU-T H.323 systems Amendment 1 Improvements for NAT traversal without intermediary entities 1 Scope This Recommendation defines the capability and procedures for enabling the direct point-to-point media flow between endpoints even if at least one device is behind a network address t
28、ranslator (NAT) or firewall (FW) device. If used in conjunction with ITU-T H.460.23, this feature can be used to extend the scalability of ITU-T H.460.19 to allow media, where determined, to flow directly between endpoints and avoid the requirement to proxy media. 2 References The following ITU-T Re
29、commendations 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 revision; users of this Recommendation are
30、 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 this Recommendation does not give it, as a
31、 stand-alone document, the status of a Recommendation. ITU-T H.225.0 Recommendation ITU-T H.225.0 (2009), Call signalling protocols and media stream packetization for packet-based multimedia communication systems. ITU-T H.245 Recommendation ITU-T H.245 (2009), Control protocol for multimedia communi
32、cation. ITU-T H.323 Recommendation ITU-T H.323 (2009), Packet-based multimedia communications systems. ITU-T H.460.1 Recommendation ITU-T H.460.1 (2002), Guidelines for the use of the generic extensible framework. ITU-T H.460.17 Recommendation ITU-T H.460.17 (2005), Using H.225.0 call signalling con
33、nection as transport for H.323 RAS messages. ITU-T H.460.18 Recommendation ITU-T H.460.18 (2005), Traversal of H.323 signalling across network address translators and firewalls. ITU-T H.460.19 Recommendation ITU-T H.460.19 (2005), Traversal of H.323 media across network address translators and firew
34、alls. ITU-T H.460.23 Recommendation ITU-T H.460.23 (2009), Network address translator and firewall device determination in H.323 systems. IETF RFC 3174 IETF RFC 3174 (2001), US Secure Hash Algorithm 1 (SHA1). IETF RFC 3489 IETF RFC 3489 (2003), STUN Simple Traversal of User Datagram Protocol (UDP) T
35、hrough Network Address Translators (NATs). 2 Rec. ITU-T H.460.24 (2009)/Amd.1 (05/2011) NOTE The IETF published a new RFC that obsoletes IETF RFC 3489, changing the name of the standard and the procedures defined therein. This Recommendation relies on the protocol and procedures specified in IETF RF
36、C 3489, and the protocol and procedures defined in the new RFC are neither suitable nor compatible. As such, this Recommendation does not reference the new RFC and deliberately makes reference to the original specification, which is now referred to as “classical STUN“. IETF RFC 3550 IETF RFC 3550 (2
37、003), RTP: A Transport Protocol for Real-Time Applications. IETF RFC 3711 IETF RFC 3711 (2004), The Secure Real-time Transport Protocol (SRTP). 3 Definitions 3.1 Terms defined elsewhere This Recommendation uses the following terms defined elsewhere: 3.1.1 transport address ITU-T H.323: The transport
38、 layer address of an addressable ITU-T H.323 entity as defined by the (inter)network protocol suite in use. The Transport Address of an ITU-T H.323 entity is composed of the Network Address plus the transport layer service access point identifier of the addressable ITU-T H.323 entity. 3.2 Terms defi
39、ned in this Recommendation This Recommendation defines the following terms: 3.2.1 P2Pnat media: Indicates that media flows directly (peer-to-peer) between two communicating endpoints through NAT devices without the assistance of a media proxy. 3.2.2 pinhole: A temporary binding of an internal and an
40、 external transport address in the network address translator/firewall, which allows the bidirectional passage of packets between those addresses. 3.2.3 STUN server: A server to assist in network address translator type detection. 3.2.4 well-behaved NAT: A network address translator (NAT) that exhib
41、its consistent behaviour over time of a given NAT type as categorized in clause 5 of IETF RFC 3489. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: ACF Admission Confirm ARJ Admission Reject ARQ Admission Request CUI Channel Unique Identifier EP Endpoi
42、nt FW Firewall GEF Generic Extensibility Framework LAN Local Area Network LCF Location Confirm LRQ Location Request NAT Network Address Translator Rec. ITU-T H.460.24 (2009)/Amd.1 (05/2011) 3 OID Object Identifier OLC Open Logical Channel message OLCAck Open Logical Channel Acknowledge message PER P
43、acked Encoding Rules RTCP Real-time Transport Control Protocol RTP Real-time Transport Protocol SR Sender Report SRTCP Secure Real-Time Transport Control Protocol SRTP Secure Real-time Transport Protocol STUN Simple Traversal of User datagram protocol through Network address translators TCP Transmis
44、sion Control Protocol TSAP Transport layer Service Access Point UDP User Datagram Protocol 5 Feature description This Recommendation defines a procedure wherein gatekeepers may negotiate between each other to determine a method to traverse media between endpoints where at least one of these endpoint
45、s is located behind a NAT/FW device, without requiring the use of an ITU-T H.460.19 server to proxy media. This Recommendation is designed for use in networks that employ NAT/FW devices with well-behaved NAT characteristics. Networks that do not employ well-behaved NAT devices should continue to uti
46、lize ITU-T H.460.18 and ITU-T H.460.19 to ensure proper end-to-end media flows. 6 Capability advertisement Endpoints capable of supporting P2Pnat media shall advertise this capability via the generic extensibility framework (GEF) defined in ITU-T H.323 and ITU-T H.460.1. This feature shall be used i
47、n conjunction with ITU-T H.460.23 NAT/FW determination and ITU-T H.460.18 (or optionally ITU-T H.460.17) as an alternative to ITU-T H.460.19. Endpoints seeking to support this feature shall also support ITU-T H.460.23 and ITU-T H.460.18/ITU-T H.460.19 or optionally ITU-T H.460.17/ITU-T H.460.19. If
48、ITU-T H.460.18 or optionally ITU-T H.460.17 and ITU-T H.460.23 features are unsupported or unavailable, then this feature shall be disabled and shall not advertised. Endpoints shall advertise the P2Pnat media feature when sending an ARQ to a gatekeeper. The feature indicator shall be included in the
49、 supportedFeatures field of the featureSet field and, if or when instructed by the gatekeeper via the replying ACF message, the feature indicator shall also be to include as a supportedFeatures field in the Setup message when placing calls to remote endpoints. The gatekeeper shall also advertise this capability to other gatekeepers via the generic data field contained in the LRQ and responding LCF messages. NOTE The advertisement and use of ITU-T H.460.19 shall be determ
