1、 International Telecommunication Union ITU-T H.248.49TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (08/2007) SERIES H: AUDIOVISUAL AND MULTIMEDIA SYSTEMSInfrastructure of audiovisual services Communication procedures Gateway control protocol: Session description protocol RFC and capabilities packa
2、ges ITU-T Recommendation H.248.49 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 Com
3、munication 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 audiovisual
4、and multimedia services 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 collab
5、oration 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.559Mobile multimedia collaboration inter-working procedures H.560H.569
6、 BROADBAND AND TRIPLE-PLAY MULTIMEDIA SERVICES Broadband multimedia services over VDSL H.610H.619 For further details, please refer to the list of ITU-T Recommendations. ITU-T Rec. H.248.49 (08/2007) i ITU-T Recommendation H.248.49 Gateway control protocol: Session description protocol RFC and capab
7、ilities packages Summary ITU-T Recommendation H.248.1 uses the session description protocol (SDP) to convey information in the local and remote descriptors of the text encoding of the protocol. Typically this SDP has been based on the use of IETF RFC 2327. New variants of SDP have been developed whi
8、ch contain some incompatibilities with IETF RFC 2327. ITU-T Recommendation H.248.49 allows a media gateway controller to firstly determine which SDP IETF RFC the media gateway is compliant to, as well as being able to determine the SDP capabilities. This allows greater interoperability between the m
9、edia gateway controller and media gateway. Source ITU-T Recommendation H.248.49 was approved on 29 August 2007 by ITU-T Study Group 16 (2005-2008) under the ITU-T Recommendation A.8 procedure. ii ITU-T Rec. H.248.49 (08/2007) FOREWORD The International Telecommunication Union (ITU) is the United Nat
10、ions 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, operating and tariff questions and issuing Recommendations
11、 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, produce Recommendations on these topics. The approval o
12、f 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 this Recommendation, the expression “Administration“ i
13、s 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., interoperability or applicability) and compliance with
14、 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 suggest that compliance with the Recommendation is required
15、 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 evidence, validity or applicability of claimed Intellectual
16、 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, protected by patents, which may be required to implement this Recommendation. Howeve
17、r, 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 2008 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prio
18、r written permission of ITU. ITU-T Rec. H.248.49 (08/2007) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Terms and definitions . 2 3.1 Terms defined elsewhere 2 3.2 Terms defined in this Recommendation. 2 4 Abbreviations and acronyms 2 5 Conventions 2 6 Session Description Protocol RFC Package. 2 6.
19、1 Properties 3 6.2 Events . 3 6.3 Signals 3 6.4 Statistics 3 6.5 Error codes 3 6.6 Procedures 3 7 Session description protocol capabilities package 5 7.1 Properties 5 7.2 Events . 10 7.3 Signals 10 7.4 Statistics 10 7.5 Error codes 10 7.6 Procedures 11 Appendix I Comparison of SDP variants between R
20、FC 4566 and RFC 2327 . 12 I.1 Introduction 12 I.2 RFC 4566 versus RFC 2327. 13 I.3 Specific impact on H.248/SDP. 20 ITU-T Rec. H.248.49 (08/2007) 1 ITU-T Recommendation H.248.49 Gateway control protocol: Session description protocol RFC and capabilities packages 1 Scope When the text encoding of ITU
21、-T H.248.1 is used, local descriptors (LD) and remote descriptors (RD) consisting of “session“ descriptions are based on the session description protocol (SDP) (clause 7.1.8 of ITU-T H.248.1). As a result, SDP information elements are embedded in the H.248 protocol syntax. The encoder/decoder for H.
22、248 Messages for Annex B of ITU-T H.248.1 text mode therefore comprises of an SDP encoder/decoder in addition to the basic H.248 encoder/decoder. There are multiple versions of H.248.1, and multiple variants of SDP IETF RFC 2327, and IETF RFC 4566. H.248 versions and SDP variants are orthogonal in t
23、he sense, that principally any H.248 version could be operated with any SDP variant. However, there are dependencies due to the history concerning the different timelines of H.248.1 and SDP developments, e.g.,: H.248.1 Version 1 (03/2002) is based on SDP IETF RFC 2327; H.248.1 Version 2 (05/2002) is
24、 based on SDP IETF RFC 2327; or H.248.1 Version 3 (09/2005) is based on SDP IETF RFC 2327. The protocol versioning of H.248 and SDP, as well as backward compatibility, requires a negotiation mechanism to select a common H.248 protocol version as well as a common SDP RFC for the text-based encoding o
25、f LD and RD on MGC and MG side. Whereas H.248 protocol version negotiation is already supported by H.248 ServiceChange elements, an explicit mechanism is still missing for SDP version determination. This Recommendation enables a media gateway controller to determine which SDP RFC a media gateway sup
26、ports. Once the SDP RFC has been determined the media gateway controller can then indicate to the media gateway which SDP RFC version it will use. SDP based on IETF RFC 4566 may be of use when a media gateway controller is already using IETF RFC 4566 in its call/session control protocols. By setting
27、 a particular SDP RFC version, the MG will behave as if all references in H.248.1 to the use of IETF RFC 2327 have been replaced by that particular version of SDP RFC. In order for media gateway controllers and media gateways to be backward compatible, they shall support IETF RFC 2327 even if a new
28、SDP RFC is also supported. In addition to providing a capability to determine the supported SDP RFC, this Recommendation provides the capability to determine which SDP parameters the MG supports. 2 References The following ITU-T Recommendations and other references contain provisions which, through
29、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 therefore encouraged to investigate the possibility of applying the
30、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 stand-alone document, the status of a Recommendation. ITU-T H.248.1
31、ITU-T Recommendation H.248.1 (2005), Gateway control protocol: Version 3. 2 ITU-T Rec. H.248.49 (08/2007) IETF RFC 2327 IETF RFC 2327 (1998), SDP: Session Description Protocol. IETF RFC 3266 IETF RFC 3266 (2002), Support for IPv6 in Session Description Protocol (SDP). IETF RFC 4566 IETF RFC 4566 (20
32、06), SDP: Session Description Protocol. 3 Terms and definitions 3.1 Terms defined elsewhere None. 3.2 Terms defined in this Recommendation This Recommendation defines the following terms: 3.2.1 AuditCapabilities.req: H.248.1 AuditCapabilities command request. 3.2.2 AuditValue.req: H.248.1 AuditValue
33、 command request. 3.2.3 SDP RFC: The IETF RFCs for SDP specifications are not explicitly denoted as “protocol versions“ (Note 1). The H.248.49 property “SDP RFC“ shall be related to the definition. NOTE 1 The SDP “v=“ line is aimed at signalling the SDP protocol version. Nevertheless, all existing S
34、DP RFCs IETF RFC 2327 and IETF RFC 3266 define protocol version 0 (see clause 5.1 in IETF RFC 4566: “The “v=“ field gives the version of the Session Description Protocol. This memo defines version 0. There is no minor version number.“) NOTE 2 The SDP “o=“ line contains the “version number of the ses
35、sion description“ (field ). This session version should not be confused with the SDP or H.248.1 protocol version. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: LD Local Descriptor MG Media Gateway MGC Media Gateway Controller RD Remote Descriptor SDP
36、 Session Description Protocol 5 Conventions None. 6 Session Description Protocol RFC Package Package Name: Session Description Protocol RFC PackageID: sdpr (0x00bb) Description: This package allows the MGC to determine which SDP RFCs the MG supports. It also allows the MGC to choose and indicate to
37、the MG which SDP RFC both the MG and the MGC can support and shall use for the control association. Version: 1 Extends: None ITU-T Rec. H.248.49 (08/2007) 3 6.1 Properties 6.1.1 SDP RFC Property Name: SDP RFC PropertyID: RFC (0x0001) Description: This property indicates the supported SDP RFC. Type:
38、Integer Possible values: The IETF RFC number that defines the SDP RFC. E.g., 2327 for RFC 2327 3266 for RFC 3266 NOTE Support of RFC 3266 implies support of RFC 2327 also. 4566 for RFC 4566 Default: 2327 Defined in: TerminationState (Root Termination only) Characteristics: Read/Write 6.2 Events None
39、. 6.3 Signals None. 6.4 Statistics None. 6.5 Error codes 6.5.1 Invalid SDP Syntax Error Code #: 474 Name: Invalid SDP Syntax Definition: The SDP received by the MG contains invalid or unexpected syntax according to the expected SDP RFC syntax. Error Text in the Error Descriptor: None Comment: The co
40、mmand is disregarded. 6.6 Procedures 6.6.1 Version determination and specification As a general rule, upon establishment of a new H.248 control association and before the MGC has modified the MGs Root termination LocalControl descriptor property sdpr/RFC, both the MGC and the MG should implicitly as
41、sume that the default SDP IETF RFC 2327 is used within this H.248 control association where ITU-T H.248.1 version 1, 2 or 3 is used. However, this default may change if a H.248 profile is negotiated. 4 ITU-T Rec. H.248.49 (08/2007) If the MGC wants to modify the SDP RFC to be used within this H.248
42、control association, it should first send an AuditCapability request for the Root termination with an Audit descriptor containing the LocalControl sdpr/RFC property, e.g., AuditCapability = ROOT Audit Media LocalControl sdpr/RFC The MGs reply would then contain a list of all possible SDP RFC values
43、the MG supports according to clause 7.2.6 of ITU-T H.248.1. The MGC may then issue a Modify request for the Root termination containing a LocalControl descriptor including the sdpr/RFC property with a single property value which should be equal to one of the values contained in the list the MG retur
44、ned in the AuditCapability response. If the MG supports the requested SDP RFC, according to standard ITU-T H.248.1 rules, it answers positively to the Modify request. From this point in time onwards, the SDP exchanged between MGC and MG in local and remote descriptors is understood to comply to the
45、SDP RFC set by the MGC in the Modify command on the Root termination. This is applicable to both text and binary implementations as binary implementations may use Annex C of ITU-T H.248.1 SDP properties. It is not recommended to change the Root termination property sdpr/RFC after the first call-rela
46、ted H.248 context had been created within the newly established H.248 control association. The MGC should only modify the sdpr/RFC property of the Root termination immediately after any ServiceChange procedure resulting in the setting or negotiation of the H.248.1 version and before the first local
47、or remote descriptor is being exchanged between MGC and MG. If terminations are already instantiated at the setting of the sdpr/RFC property, the MGC and MG shall use the new SDP RFC for these terminations. If mismatches occur between the old and new SDP RFCs for these terminations for subsequent si
48、gnalling altering the local and remote descriptors, then error code 474 “Invalid SDP Syntax“ should be used. 6.6.2 Unsuccessful root property modification If the MG receives a Modify request for the Root termination containing an unsupported sdpr/RFC SDP RFC value, it should answer with error code 4
49、49 “Unsupported or Unknown Parameter or Property value“. In this case, the value of the sdpr/RFC property remains unchanged and the previously used SDP RFC syntax continues to the used. 6.6.3 Unsuccessful LD or RD descriptor modification If the MG receives a Modify request to modify the LD or RD encoded according to a non-set SDP RFC value, it should answer with error code 474 “Invalid SDP Syntax“. ITU-T Rec. H.248.49 (08/2007) 5 7 Session description protocol capabilities packa
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