1、 International Telecommunication Union ITU-T H.248.84TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (07/2012) SERIES H: AUDIOVISUAL AND MULTIMEDIA SYSTEMSInfrastructure of audiovisual services Communication procedures Gateway control protocol: NAT traversal for peer-to-peer services Recommendation
2、ITU-T H.248.84 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 procedur
3、es 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 servi
4、ces 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 applications
5、 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 IPT
7、V 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.248.84 (07/2012) i Recommendation ITU-T H.248.84 Gateway control protocol: NAT traversal for peer-to-peer services Summary Session border controllers (SBCs) are an important part of the Internet infrastructure. Some of these session border controllers are split
9、 into media gateway controller (MGC) and media gateway (MG) components. One important function of an SBC is to perform traversal support for remote network address/port translation (NAT) devices in the IP communication path. Recommendation ITU-T H.248.84 defines an additional tool for NAT traversal
10、for peer-to-peer (P2P) services and an initial focus on TCP-based applications. History Edition Recommendation Approval Study Group 1.0 ITU-T H.248.84 2012-07-22 16 ii Rec. ITU-T H.248.84 (07/2012) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in t
11、he 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 studying technical, operating and tariff questions and issuing Recommendations on them with a view to stan
12、dardizing 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 groups which, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is c
13、overed 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 with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to in
14、dicate both a telecommunication administration and a recognized operating agency. Compliance 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 achi
15、eved 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 such words does not suggest that compliance with the Recommendation is required of any party. INTELLECTUAL
16、 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 position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether a
17、sserted 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, protected by patents, which may be required to implement this Recommendation. However, implementers are caution
18、ed 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 of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU
19、. Rec. ITU-T H.248.84 (07/2012) iii Table of Contents Page 1 Scope 1 1.1 Problem statement 1 1.2 Example network applications . 1 2 References. 2 3 Definitions 2 3.1 Terms defined elsewhere 2 3.2 Terms defined in this Recommendation . 3 4 Abbreviations 3 5 Conventions 4 5.1 Conventions concerning th
20、e ITU-T H.248 gateway control protocol 4 5.2 Conventions concerning the TCP bearer protocol 5 5.3 Conventions concerning the SIP Call control protocol 5 6 NAT-traversal for peer-to-peer services . 5 6.1 Overview 5 6.2 Protocol dependencies 7 7 Example use cases 7 7.1 TCP bearer path with SIP signall
21、ing path 7 8 NAT-traversal peer-to-peer package 9 8.1 Properties 9 8.2 Events . 9 8.3 Signals 10 8.4 Statistics 10 8.5 Error codes 10 8.6 Procedures 10 9 TCP hole punching package . 10 9.1 Properties 11 9.2 Events . 11 9.3 Signals 12 9.4 Statistics 12 9.5 Error codes 13 9.6 Procedures 13 10 TCP traf
22、fic volume metrics package 13 10.1 Properties 13 10.2 Events . 13 10.3 Signals 13 iv Rec. ITU-T H.248.84 (07/2012) Page 10.4 Statistics 14 10.5 Error codes 15 10.6 Procedures 15 11 TCP connection control metrics package . 15 11.1 Properties 15 11.2 Events . 16 11.3 Signals 16 11.4 Statistics 16 11.5
23、 Error codes 17 11.6 Procedures 17 12 TCP connection quality metrics package . 17 12.1 Properties 17 12.2 Events . 18 12.3 Signals 18 12.4 Statistics 18 12.5 Error codes 18 12.6 Procedures 19 13 Package-independent procedures for NAT-T with TCP bearers 19 13.1 TCP mode of operation: decision baselin
24、e in MGC . 19 13.2 TCP mode of operation: control principle at ITU-T H.248 interface . 19 13.3 Supported connection model 19 13.4 Indication of IP transport protocol TCP 20 13.5 Indication of TCP mode for ITU-T H.248 MG 20 13.6 TCP connection reuse . 21 13.7 TCP connection establishment phase Handli
25、ng of TCP Protocol Control Information by the ITU-T H.248 MG 21 13.8 Unsuccessful NAT-T scenarios 22 13.9 Impact of transport protocol encryption . 22 13.10 Interactions with NAT-T method latching/relatching 23 13.11 Possible interactions with enabled filters for TCP traffic 23 14 Package-independen
26、t, bearer-independent procedures for NAT-T 23 14.1 Relations to latching/relatching based NAT traversal support . 23 14.2 Interaction with L4 filters . 23 Appendix I Example signalling scenarios . 25 I.1 Example signalling for use case “TCP bearer path with SIP signalling path“ 25 Rec. ITU-T H.248.8
27、4 (07/2012) v Page Appendix II TCP Functions versus ITU-T H.248 TCP modes of operation 32 II.1 Purpose and scope 32 II.2 Overview 32 II.3 Tables of TCP functions versus ITU-T H.248 TCP modes of operation . 33 II.4 Relation between TCP proxy and TCP merge mode 38 Appendix III TCP mode control SDP “a=
28、setup“ clarification due to b-IETF RFC 6135 40 Appendix IV Generic NAT traversal models . 41 IV.1 ITU-T H.248 gateways in SIP environments and remote NAT devices 41 IV.2 Basic types of remote NAT devices . 42 IV.3 Local NAT function by ITU-T H.248 MG and end-to-end consideration . 43 Appendix V Illu
29、stration of performance measurements . 46 V.1 Statistic “TCP connection establishment delay (in TCP merge mode)“ 46 V.2 Statistic “TCP round-trip time during connection establishment phase“ . 47 Bibliography. 50 Rec. ITU-T H.248.84 (07/2012) 1 Recommendation ITU-T H.248.84 Gateway control protocol:
30、NAT traversal for peer-to-peer services 1 Scope NAT traversal (NAT-T) support by ITU-T H.248 media gateways (MG) is an established capability for such network elements positioned in the IP infrastructure of next generation networks (NGN) and IP multimedia subsystem (IMS) networks. In ITU-T H.248 the
31、re are several methods for NAT-T, for example: ITU-T H.248.37 IP NAPT traversal package; and ITU-T H.248.50 NAT traversal toolkit packages. However, these do not define any methods for NAT-T in peer-to-peer (P2P) services, i.e., for ITU-T H.248 MGs located within the end-to-end P2P IP path providing
32、 NAT traversal support for remote NAT devices (also located in the P2P IP path). In scope of this Recommendation are NAT-T techniques as detailed by b-IETF RFC 5128. 1.1 Problem statement The problem of providing NAT-T in P2P is described in b-IETF RFC 5128. However, this IETF RFC does not consider
33、scenarios where ITU-T H.248 gateways may be located in the end-to-end IP paths of a P2P service. The ITU-T H.248 MG may provide help for NAT-T, e.g., by the capability of reporting observed IP transport addresses according to the ITU-T H.248.37 address reporting package; or/and a bearer-level applic
34、ation level gateway (ALG) function according to ITU-T H.248.78. However, the usage of either or both is conditional, dependent on: network architecture, IP applications, protocol awareness by ITU-T H.248 MG, remote NAT behaviour, etc. It should also be noted that a bearer-level application layer gat
35、eway (ALG) itself may not be sufficient for NAT-T scenarios in scope of this Recommendation. The bearer-level ALG might be a beneficial and effective NAT-T support function. However this Recommendation provides NAT-T methods for scenarios without the usage of ITU-T H.248.78. This is in order to resp
36、ect the principle of “network unawareness“ (i.e., “L4 payload agnostic“) concerning the (bearer-level) IP application protocol in P2P scenarios. 1.2 Example network applications Example network applications are for instance, ITU-T H.248 gateways located between different IP networks (so called ITU-T
37、 H.248 border gateways) which support over-layered peer-to-peer services. 2 Rec. ITU-T H.248.84 (07/2012) 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 publi
38、cation, the editions indicated were valid. All Recommendations and other references are subject to revision; 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 th
39、e currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T H.248.1 Recommendation ITU-T H.248.1 (2005), Gateway control protocol: Version 3, including Amendm
40、ent 2 (12/2009). ITU-T H.248.37 Recommendation ITU-T H.248.37 (2008), Gateway control protocol: IP NAPT traversal package. ITU-T H.248.40 Recommendation ITU-T H.248.40 (2007), Gateway control protocol: Application data inactivity detection package. ITU-T H.248.50 Recommendation ITU-T H.248.50 (2010)
41、, Gateway control protocol: NAT traversal toolkit packages. ITU-T H.248.69 Recommendation ITU-T H.248.69 (2009), Gateway control protocol: Packages for interworking between MSRP and H.248. ITU-T H.248.78 Recommendation ITU-T H.248.78 (2010), Gateway control protocol: Bearer-level application level g
42、ateway. ETSI TS 123 228 ETSI TS 123 228 V10.7.0 (2012-01), Digital cellular telecommunications system (Phase 2+); Universal Mobile Telecommunications System (UMTS); LTE; IP Multimedia Subsystem (IMS); Stage 2 (3GPP TS 23.228 version 10.7.0 Release 10). IETF RFC 793 IETF RFC 793 (1981), Transmission
43、Control Protocol. IETF RFC 4145 IETF RFC 4145 (2005), TCP-Based Media Transport in the Session Description Protocol (SDP). IETF RFC 4975 IETF RFC 4975 (2007), The Message Session Relay Protocol (MSRP). IETF RFC 5382 IETF RFC 5382 (2008), NAT Behavioral Requirements for TCP. 3 Definitions 3.1 Terms d
44、efined elsewhere This Recommendation uses the following terms defined elsewhere: 3.1.1 application level gateway (ALG) ETSI TS 123 228: An application specific functional entity that allows communication between disparate address realms or IP versions, e.g., an IPv6 node to communicate with an IPv4
45、node and vice versa, when certain applications carry network addresses in the payloads like SIP/SDP. NA(P)T-PT or NA(P)T is application unaware whereas ALGs are application specific translation entities that allow a host running an application to communicate transparently with another host running t
46、he same application but in a different IP version or IP address realm. NOTE This definition originates from the first ALG description in clause 2.9 of b-IETF RFC 2663. Rec. ITU-T H.248.84 (07/2012) 3 3.1.2 transport (TCP) relay (translator) mode b-ETSI TR 183 068: Transparent forwarding of TCP packe
47、ts in terms of stateless behaviour concerning the TCP connection state machine NOTE The term transport relay translator (TRT) mode is based on b-IETF RFC 3142, which describes the IP version translation for transport protocol aware IP nodes. 3.1.3 transport (TCP) proxy (translator) mode (also known
48、as back-to-back TCP endpoint (B2BTE) mode) b-ETSI TR 183 068: Stateful forwarding of TCP packets in terms of full protocol termination. The end-to-end TCP connection is partitioned in two TCP connection legs by the BGF. Each ITU-T H.248 Stream endpoint provides a stateful TCP connection state machin
49、e. NOTE 1 The term proxy mode is similar as used for HTTP proxy, FTP proxy, SIP proxy, etc. NOTE 2 The term BGF relates to an ITU-T H.248 (IP, IP) media gateway in this Recommendation. 3.2 Terms defined in this Recommendation This Recommendation defines the following terms: 3.2.1 hole punching: A method of dedicated network address translator (NAT) to allow appropriately designed peer-to-peer applications to create a path
