1、 International Telecommunication Union ITU-T H.248.55TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (06/2008) SERIES H: AUDIOVISUAL AND MULTIMEDIA SYSTEMSInfrastructure of audiovisual services Communication procedures Gateway control protocol: Generic pull mode package Recommendation ITU-T H.248.55
2、 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 procedures H.240H.259
3、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 and multimedia services H.360H.36
4、9 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 and services
5、 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 BROADBAND AND TRIPLE-PLAY MULTIM
6、EDIA SERVICES Broadband multimedia services over VDSL H.610H.619 For further details, please refer to the list of ITU-T Recommendations. Rec. ITU-T H.248.55 (06/2008) i Recommendation ITU-T H.248.55 Gateway control protocol: Generic pull mode package Summary H.248 represents a resource control proto
7、col concerning the control of media gateway-level resources. There are two major categories concerning resource control strategies: push mode and pull mode. Push mode is an inherent architectural characteristic of the H.248 master-slave model, where the master entity MGC is pushing the slave entity
8、MG into a particular mode. Pull mode is also supported by the H.248 protocol architecture, but requires additional protocol elements to control a particular pull mode scenario. Recommendation ITU-T H.248.55 defines a generic set of such capabilities. Source Recommendation ITU-T H.248.55 was approved
9、 on 13 June 2008 by ITU-T Study Group 16 (2005-2008) under Recommendation ITU-T A.8 procedure. ii Rec. ITU-T H.248.55 (06/2008) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technolo
10、gies (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 standardizing telecommunications on a worldwide basis. The World Telecommu
11、nication 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 covered by the procedure laid down in WTSA Resolution 1. In some areas
12、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 indicate both a telecommunication administration and a recognized operat
13、ing 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 achieved when all of these mandatory provisions are met. The words “shall“ o
14、r 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 PROPERTY RIGHTS ITU draws attention to the possibility that the practic
15、e 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 asserted by ITU members or others outside of the Recommendation developme
16、nt 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 cautioned that this may not represent the latest information and are therefore
17、strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2009 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.248.55 (06/2008) iii CONTENTS Page 1 Scope 1 2 References
18、. 1 3 Terms and Definitions 1 3.1 Terms defined elsewhere 1 3.2 Terms defined in this Recommendation. 2 4 Abbreviations and acronyms 2 5 Conventions 2 6 Resource control framework. 2 6.1 Background. 2 6.2 Resource control mechanisms 3 6.3 Summary. 8 7 Generic pull mode package 9 7.1 Properties 9 7.2
19、 Events . 10 7.3 Signals 12 7.4 Statistics 12 7.5 Error codes 12 7.6 Procedures 12 8 Resource control scenarios . 16 8.1 Introduction 16 8.2 Push mode 16 8.3 Context-created MG pull mode 17 8.4 Context-less MG pull mode 19 Bibliography. 21 Rec. ITU-T H.248.55 (06/2008) 1 Recommendation ITU-T H.248.5
20、5 Gateway control protocol: Generic pull mode package 1 Scope There are various resource control mechanisms used in next generation networks (NGNs) such as those described in ITU-T Y.2111. A policy control mechanism (such as QoS resource control) is described by this Recommendation. The mechanism it
21、self may result in different control scenarios that are primarily dependent on dedicated user and customer premises equipment (UE, CPE) types. This Recommendation describes how H.248 entities behave in such a network environment, and defines an H.248 package, which may be used in a specific resource
22、 control scenario. Clause 6 provides a background on resource and admission control functions (RACFs) and discusses the resource control modes. The clause then focuses on the “pull mode“ of resource control and provides a mapping of the RACF functions and flows of this mode to the H.248 architecture
23、. 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 revis
24、ion; 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 this
25、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. ITU-T H.248.13 Recommendation ITU-T H.248.13 (2002), Gateway control protocol: Quality Alert Ceasing package. ITU-T H.24
26、8.14 Recommendation ITU-T H.248.14 (2002), Gateway control protocol: Inactivity timer package. ITU-T H.248.36 Recommendation ITU-T H.248.36 (2005), Gateway control protocol: Hanging Termination Detection package. ITU-T H.248.40 Recommendation ITU-T H.248.40 (2007), Gateway control protocol: Applicat
27、ion data inactivity detection package. ITU-T Y.2111 Recommendation ITU-T Y.2111 (2006), Resource and admission control functions in next generation networks. 3 Terms and definitions 3.1 Terms defined elsewhere This Recommendation uses the following terms defined elsewhere: 3.1.1 path-coupled QoS sig
28、nalling: ITU-T Y.2111: A mode of signalling where the signalling messages follow a path that is tied to the data packets. Signalling messages are routed only through nodes that are in the data path. 3.1.2 pull mode ITU-T Y.2111: Defined in clause 6.1.2 of ITU-T Y.2111, “Scenario 2: Pull mode QoS res
29、ource control scenario“. 2 Rec. ITU-T H.248.55 (06/2008) 3.1.3 push mode ITU-T Y.2111: Defined in clause 6.1.2 of ITU-T Y.2111, “Scenario 1: Push mode QoS resource control scenario“. 3.2 Terms defined in this Recommendation This Recommendation defines the following term: 3.2.1 authorization token: A
30、 piece of information, either clear or encrypted, which can be used to validate a request for specific resources. This information is used as a unique identifier in policy pull mode. The token is generated by the MGC and may be sent back by the MG to the MGC for the re-authorization of the resource
31、request in the pull mode. NOTE The authorization token may or may not use H.248 information elements. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: ATM Asynchronous Transfer Mode CPE Customer Premises Equipment IP Internet Protocol MG Media Gateway M
32、GC Media Gateway Controller MID Message Identifier NACF Network Attachment Control Function NGN Next Generation Network PD-E Policy Decision Entity PE-E Policy Enforcement Entity PSTN Public Switched Telecommunications Network QoS Quality of Service RACF Resource and Admission Control Function SCF S
33、ervice Control Functions UE User Equipment VMG Virtual Media Gateway 5 Conventions None. 6 Resource control framework 6.1 Background Figure 1 provides a simplified model of RACFs in next generation networks. The RACF is aimed at providing real-time application-driven and policy-based transport resou
34、rce management for a wide range of services and for a variety of transport technologies. See ITU-T Y.2111 for a detailed description of the RACF subsystem within an NGN. Rec. ITU-T H.248.55 (06/2008) 3 TransportFunctionsNACFSCFUERACFLegend:NACF Network Attachment Control Functions RACF Resource and
35、Admission Control FunctionsPD-E Policy Decision EntityPE-E Policy Enforcement EntitySCF Service Control Functions UE User Equipment Scope of this RecommendationApplication signalling (e.g. call/session control protocol)RACF controlTransport/Path-coupled QoS signallingBearer connection (IP)PE-EPD-ERA
36、CF within the NGN architecture MG MGCH.248 in this RecommendationFigure 1 Simplified model of a NGN architecture Relationship to this Recommendation The policy decision entity (PD-E) and policy enforcement entity (PE-E) are elements of this network architecture and in scope of this Recommendation be
37、cause both could be mapped to H.248 entities (see b-ITU-T Q.3300 and b-ITU-T Q.3303.0). 6.2 Resource control mechanisms The RACF should support different resource control modes in order to handle different types of user equipment (UE), customer premises equipment (CPE) and/or transport QoS capabilit
38、ies (see clause 6 of ITU-T Y.2111). This clause describes those control modes and their relationship to this Recommendation. 6.2.1 Push versus pull mode There are two basic resource control modes (see clause 6.1.1 of ITU-T Y.2111): 1) Push mode: The RACF makes the authorization and resource control
39、decision based on policy rules and autonomously instructs the transport functions to enforce the policy decision. 2) Pull mode: The RACF makes the authorization decision based on policy rules and, upon the request of the transport functions, re-authorizes the resource request and responds with the f
40、inal policy decision for enforcement. The correspondent high-level resource control scenarios are summarized by Figure 2. The detailed signalling and control phases are not relevant for this Recommendation (they are outlined in ITU-T Y.2111). For information regarding messages associated with each o
41、f the numbered flows below see b-ITU-T Q-Sup.59. 4 Rec. ITU-T H.248.55 (06/2008) TransportFunctionsNACFSCFUERACFLegend:NACF Network Attachment Control Functions RACF Resource and Admission Control FunctionsSCF Service Control Functions UE User Equipment Application signalling (e.g. call/session cont
42、rol protocol)RACF controlTransport/Path-coupled QoS signallingBearer connection (IP)21875 643TransportFunctionsNACFSCFUERACF21658 943107Push mode (1)PolicyPolicyTokenTTTTPull mode (2)Figure 2 High-level resource control and policy enforcement Principles of push and pull mode From the perspective of
43、this Recommendation, the main difference between these resource control modes is related to the binding mechanism, between a call/session and associated bearer connection(s) and media flows, i.e., H.248 streams/terminations. This relates to a correlation identifier (between service and transport str
44、atum in general NGN terms), which is called authorization token (briefly token) in case of RACF. Pull mode requires the signalling of such a token between the network and the UE/CPE, but not in push mode. This Recommendation describes the pull mode operation. Push mode is already supported by H.248
45、as such, thus it is out of scope of this Recommendation. Rec. ITU-T H.248.55 (06/2008) 5 6.2.2 Pull mode variants Different token generation mechanisms The MGC (PD-E) is involved in the generation of the token. There are multiple possibilities concerning the management of tokens by the MGC. Two poss
46、ible variants providing representative examples concerning used H.248 capabilities from this Recommendation are depicted by Figure 3. Further variants are not excluded. TransportFunctionsNACFSCFUERACF21658 943107PolicyTokenTTTTTransportFunctionsNACFSCFUERACF21658 943107PolicyTokenTTTTPull mode (2.a)
47、:PD-E-initiated Token generationPull mode (2.b):SCF-triggered Token generation2- 5+Token generation 2) resource reservation; 3) resource commitment; 4) resource modification(s); 5) resource de-activation; 6) resource release; There are many descriptions of how one or multiple resource control operat
48、ions may be mapped on signalling flows (e.g., see ITU-T Y.2111). Thus, the described resource control scenarios in this clause are examples. The figures use pseudo code for the H.248 signalling elements. 8.2 Push mode Figure 10 shows a typical flow with pseudo code for push mode. This clause and exa
49、mple is only for completeness; no capabilities from this Recommendation are required. Rec. ITU-T H.248.55 (06/2008) 17 PolicyMGCPolice Decision EntityMGPolice Enforcement EntityADD.request(Context=$; Termination=$)1. Policy decision, resource reservationADD.reply(Context=x; Termination=IP/y)2. ResourcecommitmentScenario may continue with possible further resource modifications, possible resource de-activation, till resource release.NOTE - Only the 1st H.248 Termination and Stream is shown. There are at least two
