1、 INTERNATIONAL TELECOMMUNICATION UNION ITU-T H.248.31TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (04/2004) SERIES H: AUDIOVISUAL AND MULTIMEDIA SYSTEMSInfrastructure of audiovisual services Communication procedures Gateway control protocol: Adaptive jitter buffer package ITU-T Recommendation H.2
2、48.31 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
3、.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 and multimedia services H.36
4、0H.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 and ser
5、vices 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 AND TRIPLE-PLAY
6、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.248.31 (04/2004) i ITU-T Recommendation H.248.31 Gateway control protocol: Adaptive jitter buffer package Summary This Recommendation defines a
7、package that allows the media gateway controller (MGC) to specify the nominal value and the minimum value of the adaptive jitter buffer on the media gateway (MG). This package allows the MGC to specify adaptive jitter buffer value settings on a particular stream at any time throughout a call, and it
8、 allows the MGC to enable or disable the use of a jitter buffer. In addition, the package contains a set of jitter buffer metrics that are consistent with those described in IETF RFC 3611, RTP Control Protocol Extended Reports (RTCP XR). These jitter buffer metrics may be used, for example, with voi
9、ce over IP, video, and audio. The package should be used in combination with the base network package that defines the maximum value for the jitter buffer. An adaptive jitter buffer (AJB) is characterized by these minimum, maximum, and nominal values. The AJB functions in a MG to smooth the play out
10、 of packets arriving at the MG. As the packet arrival delay varies during the course of the transmission, the jitter buffer adapts using the minimum, maximum, and nominal values to control the adaptation. Real time media requirements are stringent and, for that reason, it is important to set the jit
11、ter buffer values to their optimal setting as early on the call as possible since a jitter buffer that is too large will introduce unnecessary bearer delay, which has a negative impact on real time media quality, and a jitter buffer that is too small will prevent a smooth play out (packet loss, anot
12、her negative impact). The proper jitter buffer size is the balance between delay and packet loss. The distortion that the media receiver would otherwise observe is eliminated with the AJB. Source ITU-T Recommendation H.248.31 was approved on 22 April 2004 by ITU-T Study Group 16 (2001-2004) under th
13、e ITU-T Recommendation A.8 procedure. ii ITU-T Rec. H.248.31 (04/2004) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is
14、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 Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by
15、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 technology which fall within ITU-Ts purview, the necessary standards are prepared on a collab
16、orative 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 with this Recommendation is voluntary. However, the Recommendation may contain certai
17、n 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 obligatory language such as “must“ and the negative equivalents are used to express requiremen
18、ts. 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 of this Recommendation may involve the use of a claimed Intellectual Property Right. IT
19、U 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 the date of approval of this Recommendation, ITU had not received notice of intellectual
20、property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. ITU 2004 All rights reserved. No part of this publicatio
21、n may be reproduced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec. H.248.31 (04/2004) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Definitions 1 4 Abbreviations 1 5 Conventions 2 5.1 Convention for Termination Identifiers in this Recommendation . 2 5.2 Convention
22、for Context Identifiers in this Recommendation. 2 6 Adaptive Jitter Buffer Package. 2 6.1 Properties 2 6.2 Events . 4 6.3 Signals 4 6.4 Statistics 4 6.5 Procedures 4 ITU-T Rec. H.248.31 (04/2004) 1 ITU-T Recommendation H.248.31 Gateway control protocol: Adaptive jitter buffer package 1 Scope This Re
23、commendation defines a package that allows the media gateway controller (MGC) to specify the nominal value and the minimum value of the adaptive jitter buffer on the media gateway (MG). This package allows the MGC to specify adaptive jitter buffer value settings on a particular stream at any time th
24、roughout a call, and it allows the MGC to enable or disable the use of a jitter buffer. In addition, the package contains a set of jitter buffer metrics that are consistent with those described in IETF RFC 3611, RTP Control Protocol Extended Reports (RTCP XR). These jitter buffer metrics may be used
25、, for example, with voice over IP, video, and audio. The package should be used in combination with the base network package that defines the maximum value for the jitter buffer. An adaptive jitter buffer (AJB) is characterized by these minimum, maximum, and nominal values. The MGC will be able to d
26、etermine more meaningful values for the adaptive jitter buffer as in a majority of cases the MGC will have the knowledge of: the network architecture, the number of contexts involved in a single call, the packet networks between contexts in a call, the characteristics of the packet delay variations,
27、 etc. This, in turn, will optimize the real time media quality and end-to-end delay of a call. Each packet can encounter a different amount of delay when traversing from end-to-end. Although the variation is somewhat random, its variance depends on the network topology. For example, the greater the
28、number of hops and the longer the distance required to make the packet transmission, the more delay is expected to get through the network and the more variance in the delay. If the MGC has knowledge of the network topology, it can adjust the jitter buffer parameters accordingly. In the case of mult
29、iple MGCs being involved in an end-to-end call, each individual MGC will be responsible for determining the appropriate jitter buffer value(s) based on its own knowledge. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, c
30、onstitute 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 most recent edition of th
31、e 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 Recommendation H.248.1 (2002), Ga
32、teway control protocol: Version 2. IETF RFC 3611 (2003), RTP Control Protocol Extended Reports (RTCP XR). 3 Definitions N/A 4 Abbreviations This Recommendation uses the following abbreviations: AJB Adaptive Jitter Buffer EPH Ephemeral 2 ITU-T Rec. H.248.31 (04/2004) IP Internet Protocol MG Media Gat
33、eway MGC Media Gateway Controller RTCP RTP Control Protocol RTCP XR RTCP Extended Reports RTP Real-time Transfer Protocol TDM Time Division Multiplex (Network) VoIP Voice over IP 5 Conventions 5.1 Convention for Termination Identifiers in this Recommendation E_x: This refers to an Ephemeral Terminat
34、ion Identifier. T_x: This refers to a TDM (Physical) Termination Identifier. Where “x“ is an alphanumeric value (e.g., O (originating), T (terminating), s (send), r (receive), s2, r2, 1, 2, 3). These are set to distinguish the different terminations within the diagram. 5.2 Convention for Context Ide
35、ntifiers in this Recommendation Cy: This refers to an H.248 Context Identifier. Where “y“ is an alphanumeric value. 6 Adaptive Jitter Buffer Package PackageID: ajb (0x007a) Version: 1 Extends: nt (0x000b) version 1 This package extends the base Network Package and allows the media gateway controller
36、 (MGC) to specify the nominal value and the minimum value of the adaptive jitter buffer on a stream in the media gateway (MG). The package also provides the ability to enable/disable a jitter buffer, and it defines properties to report extended jitter buffer metrics. 6.1 Properties 6.1.1 Minimum Jit
37、ter Buffer PropertyID: jitmin (0x0008) Description: This property sets the minimum size of the adaptive jitter buffer. Type: Integer Possible Values: Any integral number of milliseconds greater than or equal to zero Defined In: LocalControlDescriptor Characteristics: Read/Write ITU-T Rec. H.248.31 (
38、04/2004) 3 6.1.2 Nominal Jitter Buffer PropertyID: jitnom (0x0009) Description: This property sets the nominal size of the adaptive jitter buffer. Type: Integer Possible Values: Any integral number of milliseconds greater than or equal to zero. Defined In: LocalControlDescriptor Characteristics: Rea
39、d/Write 6.1.3 Enable Jitter Buffer PropertyID: enabjb (0x000a) Description: It enables/disables a jitter buffer. The type of jitter buffer enabled is indicated with Jitter Buffer Type (0x000b). If disabled, no jitter buffer is inserted. Type: Boolean Possible values: on/off Defined In: LocalControlD
40、escriptor Characteristics: Read/Write 6.1.4 Jitter Buffer Type PropertyID: type (0x000b) Description: Indicates the jitter buffer type. When the jitter buffer is adaptive, then its size is being dynamically adjusted to deal with varying levels of jitter. When non-adaptive, the jitter buffer size is
41、maintained at a fixed level. Type: Enumeration Possible values: “NO“ (0x0000) No Jitter Buffer (Default) “N“ (0x0001) Non-adaptive “A“ (0x0002) Adaptive Defined In: LocalControlDescriptor Characteristics: Read/Write 6.1.5 Current Jitter Buffer PropertyID: jitcur (0x000c) Description: This property i
42、s used to obtain the current jitter buffer size at the media gateway. Type: Integer Possible Values: Any integral number of milliseconds greater than or equal to zero Defined In: LocalControlDescriptor Characteristics: Read Only 4 ITU-T Rec. H.248.31 (04/2004) 6.1.6 Adaptation Rate PropertyID: ar (0
43、x000d) Description: The adaptation rate for the adaptive jitter buffer. This is defined as the time taken in milliseconds adjusting to a step from 30 ms to 100 ms in peak-to-peak jitter divided by twice the frame size in milliseconds. This property does not apply to non-adaptive jitter buffers and s
44、hall be 0 if the jitter buffer type is set to non-adaptive. Type: Integer Possible values: Any integral number greater than or equal to zero Defined In: LocalControlDescriptor Characteristics: Read Only 6.2 Events None. 6.3 Signals None. 6.4 Statistics None. 6.5 Procedures A jitter buffer is inserte
45、d to smooth out the delay variance that real time media packets may experience through packet transport network(s). Large jitter buffers enable a GW to tolerate longer delay variance and minimize packet loss introduced by delay. However, larger jitter buffers also introduce bearer delay, which has a
46、 negative impact on real time media quality. Therefore, it is important to optimize the insertion of jitter buffers. The nominal value is a default system value that is used at the beginning of a call. In the case of adaptive jitter buffers, the media gateway will adjust the size of the jitter buffe
47、r dynamically during the call based on the packet delay variation. To optimize the delay and packet loss, it is necessary to specify the minimum, maximum, and/or nominal values of the adaptive jitter buffer based on the known network topology of each individual call. The absolute maximum jitter buff
48、er size and the absolute minimum jitter buffer size capabilities of the media gateway may be obtained through use of AuditCapabilities of the maximum jitter buffer property jit (0x0007) and the minimum jitter buffer property jitmin (0x0008). The current jitter buffer size in use may be obtained thro
49、ugh use of AuditValue of the current jitter buffer property jitcur (0x000c). AuditValue of the maximum jitter buffer property jit (0x0007) and the minimum jitter buffer property jitmin (0x0008) will provide the current maximum and minimum jitter buffer size values. When this package is implemented, the MGC is able to, on a per stream basis: enable or disable the use of a jitter buffer; specify the type of jitter buffer to be enabled; for an adaptive jitter buffer, set the minimum and nominal jitter buffer values along with the maximum jitter buffer value (as
