1、 International Telecommunication Union ITU-T H.460.18TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (03/2013) SERIES H: AUDIOVISUAL AND MULTIMEDIA SYSTEMSInfrastructure of audiovisual services Supplementary services for multimedia Traversal of ITU-T H.323 signalling across network address translato
2、rs and firewalls Recommendation ITU-T H.460.18 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
3、.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 Directory services architecture for audiovisual and multimedia services H.350H.359 Quality of service architecture for
4、 audiovisual and multimedia services H.360H.369 Supplementary services for multimedia H.450H.499MOBILITY 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 multi
5、media collaboration applications 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 procedur
6、es 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 Ubiquitous sensor network applications and Internet of Things H.640H.649 IPTV MULTIMEDIA SERVICES AND APPLICATIONS FOR IPT
7、V 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.779 Digital Signage H.780H.789 For further de
8、tails, please refer to the list of ITU-T Recommendations. Rec. ITU-T H.460.18 (03/2013) i Recommendation ITU-T H.460.18 Traversal of ITU-T H.323 signalling across network address translators and firewalls Summary Recommendation ITU-T H.460.18 extends Recommendation ITU-T H.323 to enable ITU-T H.323
9、devices to successfully exchange signalling and establish calls, even when they are placed inside a private network behind NAT/FW devices. These extensions, when used together with the facilities of ITU-T H.460.19, enable ITU-T H.323 endpoints to traverse NAT/FW installations with no additional equi
10、pment on the customer premises. Alternatively, the ITU-T H.460.18 extensions may be implemented by a proxy server to support unmodified ITU-T H.323 endpoints. This revision introduces a number of corrections and clarifications by incorporating technical and editorial corrections from the ITU-T H.323
11、-series Implementers Guide (03/2011). History Edition Recommendation Approval Study Group 1.0 ITU-T H.460.18 2005-09-13 16 2.0 ITU-T H.460.18 2013-03-16 16 Keywords Firewall, FW/NAT, ITU-T H.323, NAT, NAT/FW, network address translator, traversal. ii Rec. ITU-T H.460.18 (03/2013) FOREWORD The Intern
12、ational 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 studying technical, ope
13、rating 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 groups which, in turn,
14、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 with ISO and IEC. NOTE In
15、 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 provisions (to ensure, e.g.
16、, 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 such words does not sug
17、gest 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 position concerning the evi
18、dence, 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 received notice of intellectual property, protected by patents, which may
19、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 of this publication may be r
20、eproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU-T H.460.18 (03/2013) iii Table of Contents Page 1 Scope 1 2 References. 1 3 Definitions 2 4 Abbreviations and acronyms 2 5 Conventions 3 6 Overview 3 7 Architecture 3 8 Registration procedure 5 8.1 Traversal se
21、rver mode selection . 5 8.2 Registration when ITU-T H.460.18 mode selected by traversal server . 6 9 Outgoing call procedure . 6 10 Incoming call procedure . 7 11 ITU-T H.245 connection establishment . 7 12 Media setup procedure 8 13 Location request (LRQ/LCF) procedure 8 14 Keep-alives . 9 15 Gener
22、ic data usage in ITU-T H.225.0 9 16 Generic parameters in ITU-T H.245 . 10 16.1 connectionCorrelation 10 Annex A Signalling traversal ASN.1 definitions for use inside ITU-T H.245 and ITU-T H.225.0 generic data messages . 12 Appendix I ASN.1 OIDs defined in this Recommendation 13 Rec. ITU-T H.460.18
23、(03/2013) 1 Recommendation ITU-T H.460.18 Traversal of ITU-T H.323 signalling across network address translators and firewalls 1 Scope This Recommendation enables ITU-T H.323 signalling to traverse NAT/FW installations. When used in conjunction with ITU-T H.460.19, this allows ITU-T H.323 endpoints
24、to communicate across NAT/FWs which would otherwise be an obstacle to multimedia communications. The ITU-T H.460.18 architecture consists of a network which is divided into an internal and an external network by a NAT/FW. Typically, the internal network will be a private network, and may be managed
25、by an organization or an individual. The external network will typically be a public network such as the Internet, but may alternatively be another private network. The ITU-T H.323 internal endpoint and the ITU-T H.460.18 external traversal server (TS) work together to enable bidirectional communica
26、tion across the NAT/FW and discover the transport addresses that have been modified by the NAT/FW. 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,
27、 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 the curre
28、ntly 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.225.0 Recommendation ITU-T H.225.0 (2009), Call signalling protocols and media stream packetization for
29、 packet-based multimedia communication systems. ITU-T H.245 Recommendation ITU-T H.245 (2011), Control protocol for multimedia communication. 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 (2013), Guidelines f
30、or the use of the generic extensible framework. ITU-T H.460.19 Recommendation ITU-T H.460.19 (2013), Traversal of ITU-T H.323 media across network address translators and firewalls. ITU-T X.680 Recommendation ITU-T X.680 (2008) | ISO/IEC 8824-1:2008, Information technology Abstract Syntax Notation O
31、ne (ASN.1): Specification of basic notation. ITU-T X.691 Recommendation ITU-T X.691 (2008) | ISO/IEC 8825-2:2008, Information technology ASN.1 encoding rules: Specification of Packed Encoding Rules (PER). 2 Rec. ITU-T H.460.18 (03/2013) 3 Definitions This Recommendation defines the following terms:
32、3.1 client gatekeeper: An ITU-T H.323 gatekeeper which initiates an ITU-T H.460.18 channel to an ITU-T H.460.18 server gatekeeper for the exchange of LRQ/LCF messages. 3.2 client gateway: An ITU-T H.323 to ITU-T H.323 gateway which requires the Signalling Traversal feature. 3.3 client proxy: An ITU-
33、T H.460.18 client gateway acting as a proxy for non-ITU-T H.460.18 endpoints. 3.4 endpoint: An ITU-T H.323 terminal, gateway or MCU. An endpoint can call and be called. It generates and/or terminates information streams. 3.5 external endpoint: An endpoint located on the external network. 3.6 externa
34、l network: A network connected to the NAT/FW through the public interface of the NAT/FW. Typically, but not limited to, the public Internet. 3.7 ITU-T H.460.18 endpoint: An endpoint with the additional functionality of an ITU-T H.460.18 client. 3.8 internal endpoint: An endpoint located on the inter
35、nal network. 3.9 internal network: A network connected to the firewall through the firewalls private interface. 3.10 pinhole: A temporary binding of an internal and an external transport address in the NAT/FW which allows the bidirectional passage of packets between those addresses. 3.11 server gate
36、keeper: An ITU-T H.323 gatekeeper which accepts an ITU-T H.460.18 channel from an ITU-T H.460.18 client gatekeeper for the exchange of LRQ/LCF messages. 3.12 server gateway: An ITU-T H.323 to ITU-T H.323 gateway which provides the Signalling Traversal feature. 3.13 server proxy: An ITU-T H.460.18 se
37、rver gateway acting as a proxy for non-ITU-T H.460.18 gatekeepers. 3.14 transport address: IP address and UDP/TCP port number. 3.15 traversal server: An ITU-T H.460.18 server gateway logically combined with an ITU-T H.460.18 server gatekeeper. The traversal server is located in the external network.
38、 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: ACF Admission Confirm ARQ Admission Request LCF Location Confirm LRQ Location Request NAT/FW Network Address Translator and/or Firewall RAS Registration, Admission and Status RCF Registration Confirm RRQ
39、 Registration Request SCI Service Control Indication Rec. ITU-T H.460.18 (03/2013) 3 SCR Service Control Response TCP Transport Control Protocol TPKT Transport Protocol Data Unit Packet TS Traversal Server 5 Conventions This Recommendation uses the following conventions: “Shall“ indicates a mandator
40、y requirement. “Should“ indicates a suggested but optional course of action. “May“ indicates an optional course of action rather than a recommendation that something take place. Reference is made throughout this Recommendation to two ITU-T H.323 endpoints: EPAand EPB. EPAis an endpoint on the intern
41、al network which implements ITU-T H.460.18. EPB is located on the external network and is not required to implement ITU-T H.460.18. 6 Overview ITU-T H.460.18 utilizes the fact that NAT/FWs are typically more lenient toward traffic sessions originating from the internal network than traffic sessions
42、originating from the external network. NAT/FWs typically permit traffic that is outbound from the internal network, and typically permit inbound traffic received in response to the original outbound traffic. ITU-T H.460.18 procedures take advantage of this to open a bidirectional “pinhole“ path for
43、a given transport address by originating traffic from the inside network. The pinhole is maintained by the transmission of traffic or, in the absence of traffic, by the periodic transmission of “keep-alive“ packets. The traversal server (TS) consists of an ITU-T H.460.18-enabled ITU-T H.323 server g
44、atekeeper and an ITU-T H.460.18 server gateway. Communication between the internal endpoint and the external TS starts with the initial outgoing RAS message (GRQ or RRQ), which establishes a pinhole for RAS traffic. This RAS channel is kept open for the duration of the endpoints registration with th
45、e external TS. During call setup, this RAS channel is used to establish an ITU-T H.225.0 TCP channel, which in turn may be used to establish an ITU-T H.245 channel. Outbound calls from the internal endpoint are established according to normal ITU-T H.323 procedures. Inbound calls from external endpo
46、ints are addressed to the external IP address at the TS. The TS does not simply open a TCP connection for ITU-T H.225.0 to the internal endpoint because the NAT/FW is likely to block such a connection. Instead, the TS uses a RAS message to request the internal endpoint to open an ITU-T H.225.0 TCP c
47、onnection to the TS. This ITU-T H.225.0 TCP connection is then used for ongoing call control, including establishment of the H.245 control channel if desired. 7 Architecture ITU-T H.460.18 makes use of an ITU-T H.460.18 endpoint or client proxy and an ITU-T H.460.18 traversal server (TS) that work t
48、ogether to enable bidirectional communication across the NAT/FW, and discover the addresses that have been modified by the NAT/FW. 4 Rec. ITU-T H.460.18 (03/2013) The ITU-T H.460.18 endpoint acts as an ITU-T H.323 endpoint combined with an ITU-T H.460.18 client functionality. The endpoint may be imp
49、lemented as a single device as shown in Figure 1, which avoids the need for additional equipment on the customer premises, or as a standard ITU-T H.323 endpoint and a separate ITU-T H.460.18 client gateway as shown in Figure 2, to support unmodified ITU-T H.323 endpoints. The TS may be implemented as a single device as shown in Figure 1, as separate devices interconnected by an unspecified protocol, or as a server proxy and server gatekeeper to support unmodified ITU-T H.323 gatekeepers as shown in Figure 2. The ser
