1、 International Telecommunication Union ITU-T Series HTELECOMMUNICATION STANDARDIZATION SECTOR OF ITU Supplement 8(05/2008) SERIES H: AUDIOVISUAL AND MULTIMEDIA SYSTEMSGateway control protocol: Guidelines for synchronized time in ITU-T H.248 domains ITU-T H-series Recommendations Supplement 8 ITU-T H
2、-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 Coding o
3、f 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.369 Supple
4、mentary 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 H.520H.
5、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 MULTIMEDIA SER
6、VICES Broadband multimedia services over VDSL H.610H.619 Advanced multimedia services and applications H.620H.629 IPTV MULTIMEDIA SERVICES AND APPLICATIONS FOR IPTV General aspects H.700H.719 IPTV terminal devices H.720H.729 For further details, please refer to the list of ITU-T Recommendations. H s
7、eries Supplement 8 (05/2008) i Supplement 8 to ITU-T H-series Recommendations Gateway control protocol: Guidelines for synchronized time in ITU-T H.248 domains Summary Supplement 8 to ITU-T H-series Recommendations defines a time coordination function that may be used by an application process and/o
8、r a gateway control protocol in a decentralized gateway environment such as ITU-T H.248 decomposed gateways. Within the working assumptions defined, this supplement establishes a time coordination function model, addressing the components of a generic time service involving communication between gat
9、eway and gateway controller entities that relate the service and generic definitions provided by this function to the user requirements. It also identifies time synchronization protocols. The scope of this supplement is on “time of day“ information, not on other elements related to timing. Further m
10、ore, the provision of time information within a local system and implementation aspects are also out of the scope of this supplement. Source Supplement 8 to ITU-T H-series Recommendations was agreed on 2 May 2008 by ITU-T Study Group 16 (2005-2008). ii H series Supplement 8 (05/2008) FOREWORD The In
11、ternational 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,
12、 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 the ITU-T study groups which, in tu
13、rn, 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. NOT
14、E In this publication, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this publication is voluntary. However, the publication may contain certain mandatory provisions (to ensure e.g. inter
15、operability or applicability) and compliance with the publication 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
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18、lement this publication. 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 2009 All rights reserved. No part of this publication may be reproduced, by any mea
19、ns whatsoever, without the prior written permission of ITU. H series Supplement 8 (05/2008) iii CONTENTS Page 1 Scope 1 1.1 Explicitly out of scope 1 2 References. 2 3 Definitions 3 3.1 Terms defined elsewhere 3 3.2 Term defined in this supplement 4 4 Abbreviations and acronyms 4 5 Conventions 5 6 P
20、roblem for distributed systems (such as decomposed gateways) . 5 6.1 General aspects for distributed systems . 5 6.2 Specific for distributed gateways (according to ITU-T H.248) . 6 6.3 Functional areas with precise temporal information between ITU-T H.248 entities. 6 7 Requirements 7 7.1 Time repre
21、sentation requirements 7 7.2 Time accuracy and precision requirements 7 7.3 Synchronization domain requirements. 8 7.4 Time distribution requirements 9 7.5 Time service reliability requirements. 9 7.6 Local clock requirements . 10 7.7 Availability requirement for accurate time after ITU-T H.248 rest
22、art or registration 10 7.8 Availability requirement for accurate time after creation of an ITU-T H.248 stream or termination. 10 8 Model 10 8.1 MGC-MG model 10 8.2 Time alignment concept for a MGC-MG pair 12 8.3 ITU-T H.248 time domain model and time alignment concept . 12 9 Possible solutions for c
23、lock coordination within ITU-T H.248 domains. 13 9.1 Introduction 14 9.2 Time synchronization in ITU-T H.248 domains 14 9.3 Structures of time synchronization subnet . 15 9.4 ITU-T H.248 Time Domain distributed over multiple time zones. 18 H series Supplement 8 (05/2008) 1 Supplement 8 to ITU-T H-se
24、ries Recommendations Gateway control protocol: Guidelines for synchronized time in ITU-T H.248 domains 1 Scope This supplement defines a time coordination function that may be used by an application process and/or a gateway control protocol in a decentralized gateway environment such as decomposed g
25、ateways according to ITU-T H.248.1. This supplement: establishes user requirements for this synchronized time in ITU-T H.248 domains; establishes a time coordination function model, addressing the components of a generic time service involving communication between gateway and gateway controller ent
26、ities, that relates the service and generic definitions provided by this function to the user requirements; identifies time synchronization protocols. This supplement does not: address the provision of time information within a local system; define the nature of any implementation intended to provid
27、e the time coordination function. The scope of this supplement is on “time of day“ information, not on other elements related to timing. 1.1 Explicitly out of scope Synchronized time is typically relevant not only for the gateway control protocol and ITU-T H.248 interfaces. Timing and synchronizatio
28、n aspects for ITU-T H.248 entities may be also required, however subsequent functions and interfaces are out of scope. 1.1.1 Transmission layer ITU-T H.248 entities are connected to packet and/or circuit networks. Timing, timing distribution and synchronization aspects in packet networks are very di
29、fferent in comparison to circuit-switched networks. Such aspects for transmission layer technologies are addressed, e.g., by ITU-T G-series Recommendations. For instance, ITU-T G.8261, ITU-T G.8262, ITU-T G.8264 could be relevant for particular deployments of ITU-T H.248 entities. The transmission l
30、ayer aspects and technologies are out of scope. 1.1.2 User plane User plane protocols may carry time information. For instance, application-level framing protocols (e.g., IETF RTP, 3GPP-specific framing protocols) for real-time transport require time synchronization elements between source and sink
31、(e.g., synchronization aspects between an RTP end system and an ITU-T H.248 RTP termination). Synchronization aspects or time alignment procedures of such types of user plane protocols are out of scope. 1.1.3 Management plane Without synchronized time, accurately correlating information between netw
32、ork elements becomes difficult, if not impossible (Note). Management and management systems for ITU-T H.248 entities are out of scope here. 2 H series Supplement 8 (05/2008) NOTE For instance, comparison of log files between network elements requires synchronized times. Particularly when it comes to
33、 security issues, reliable information may be only derived on the basis of accurate timing information. 1.1.4 Relation to technologies for high precision time distribution for IP networks This supplement makes proposals for time distribution technologies that are sufficient to cover the requirements
34、 addressed by this supplement. These technologies themselves are evolving and may be relevant for IP networks with higher precision time, but not in this supplement for the considered ITU-T H.248 control association. NOTE Such IP-specific technologies will be, e.g., developed by the IETF working gro
35、up “Transmitting Timing over IP Connections and Transfer of Clock“ (TICTOC). 2 References ITU-T G.810 Recommendation ITU-T G.810 (1996), Definitions and terminology for synchronization networks. ITU-T G.8261 Recommendation ITU-T G.8261/Y.1361 (2008), Timing and synchronization aspects in packet netw
36、orks. ITU-T G.8262 Recommendation ITU-T G.8262/Y.1362 (2007), Timing characteristics of synchronous Ethernet equipment slave clock (EEC). ITU-T G.8264 Recommendation ITU-T G.8264/Y.1364 (2008), Distribution of timing information through packet networks. ITU-T H.248.1 Recommendation ITU-T H.248.1 v3
37、(2005), Gateway control protocol: Version 3. ITU-T H.248.47 Recommendation ITU-T H.248.47 (2008), Gateway control protocol: Statistic conditional reporting package. ITU-T X.743 Recommendation ITU-T X.743 (1998) | ISO/IEC 10164-20:1999, Information technology Open Systems Interconnection Systems Mana
38、gement: Time Management Function. ITU-T X.751 Recommendation ITU-T X.751 (1995) | ISO/IEC 10164-17:1996, Information technology Open Systems Interconnection Systems Management: Changeover function. ITU-T Y.1540 Recommendation ITU-T Y.1540 (2007), Internet protocol data communication service IP packe
39、t transfer and availability performance parameters. ETSI TR 183 025 ETSI TR 183 025 (2007), Telecommunications and Internet converged Services and Protocols for Advanced Networking (TISPAN); H.248 Non-Call Related Procedures and Management System Interaction. H series Supplement 8 (05/2008) 3 IETF R
40、FC 3339 IETF RFC 3339 (2002), Date and Time on the Internet: Timestamps. IETF RFC 1305 IETF RFC 1305 (1992), Network Time Protocol (Version 3) Specification, Implementation and Analysis. IETF RFC 4330 IETF RFC 4330 (2006), Simple Network Time Protocol (SNTP) Version 4 for IPv4, IPv6 and OSI. IETF RF
41、C 3550 IETF RFC 3550 (2003), RTP: A Transport Protocol for Real-Time Applications. ISO 8601 ISO 8601:2004, Data elements and interchange formats Information interchange Representation of dates and times. 3 Definitions 3.1 Terms defined elsewhere This supplement uses the following terms defined elsew
42、here: 3.1.1 actual clock rate ITU-T X.743: The actual clock rate is the frequency or rate at which a clock increments, including any modifications resulting from frequency adjustment or clock training. The actual clock rate is equivalent to the basic clock rate in the absence of or prior to any freq
43、uency adjustment modifications. 3.1.2 accuracy ITU-T X.743: Accuracy is a measure of how well a local clocks time value and frequency compare to UTC. 3.1.3 adjustment rate ITU-T X.743: Adjustment rate is the frequency or rate at which a single time adjustment is applied to the local clock. 3.1.4 bas
44、ic clock rate ITU-T X.743: The basic clock rate is the frequency or rate at which a clock increments in the absence of any modifications resulting from frequency adjustment. 3.1.5 coordinated universal time (UTC) ITU-T X.743: The time reference that is assumed to be universally correct. UTC was adop
45、ted by CCIR Recommendation 470 and described in CCIR Report 517. This is not the ASN.1 representation of generalized time. 3.1.6 correct clock ITU-T X.743: A clock where the absolute value of the error is less than its maximum error. 3.1.7 frequency offset ITU-T X.743: The first derivative of the cl
46、ocks error. That is, the frequency offset is the actual rate of change of error of the clock. 3.1.8 error of a clock ITU-T X.743: The time offset between the clocks reading and UTC at a given instant. 3.1.9 functioning clock ITU-T X.743: A clock in which either the frequency offset is within the max
47、imum frequency error of the clock or the clock is undergoing an adjustment. A functioning clock may be correct or incorrect. 3.1.10 granularity ITU-T X.743: The maximum precision permitted by a representation of time. 3.1.11 local clock ITU-T X.743: The collection of hardware and software that compr
48、ises a local source of time for a system. 4 H series Supplement 8 (05/2008) 3.1.12 maximum drift of a clock ITU-T X.743: The manufacturers specified maximum value of frequency offset. 3.1.13 maximum error of a clock ITU-T X.743: The maximum error bound of the absolute value of the error of a clock.
49、3.1.14 precision ITU-T X.743: The smallest value by which a clock changes. 3.1.15 rapport ITU-T X.743: The state when the local clock is correct and the maximum error of the clock is within the user specified maximum error. 3.1.16 synchronization domain ITU-T X.743: The set of local clocks involved in the exchange of time information for the purposes of coordination. This includes local clock and clock coordination resources. The members of this set
