1、ITU-T RECNNtH-244 95 M 4862593 ObOBLbb 449 = INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU H.244 (07/95) TRANSMISSION OF NON-TELEPHONE SIGNALS SYNCHRONIZED AGGREGATION OF MULTIPLE 64 OR 56 kbis CHANNELS ITU-T Recommendation H.244 (Previously “CCITT Recom
2、mendation”) FOREWORD The IT-T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (IT). The IT-T is responsible for studying technical, operating and tariff questions and issuing Recommen- dations on them with a view to standardizing telecommu
3、nications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. The approval of Recommendations by the Members of the
4、 -T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993). IT-T Recommendation H.244 was prepared by ITU-T Study Group 15 (1993-1996) and was approved under the WTSC Resolution No. 1 procedure on the 10th of July 1995. NOTE In this Recommendation, the expression
5、 “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. O ITU 1996 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and
6、 microfilm, without permission in writing from the ITU. CONTENTS 1 Scope 2 Normative references . 3 Definitions and symbols . 3.1 Definitions 3.2 Symbols 4 Abbreviations . 5 General . Application of this Recommendation . 5.1.1 Intercommunication of Audiovisual equipments 5.1.2 5.2 Definition of the
7、Modes of transmission on the MC side . 5.3 General description of the aggregation process 5.4 CAU functionality 6 Choice of H.244 or IS0 aggregation 7 H.244 aggregation procedure . 7.1 Call control . 7.1.1 Initial channel 7.1.2 Additional channels In-band procedure using H.22 1 BAS codes . 7.3.1 Con
8、trol of transfer rate 7.3.2 Determination of the transfer-rate capabilities to be transmitted on the MC side . 7.3.3 Determination of the transfer-rate capabilities to be transmitted on the SC side 7.3.4 Capability sets transmitted from a CAU . 7.3.5 Notification of change of Na . 7.3.6 Commands tra
9、nsmitted from a CAU . 7.4 Transmission of user information by a CAU Initialisation, ModeRate changing and Fault recovery . 8.1 Initialisation 8.1.1 Single-channel Side 8.1.2 Multi-channel Side, initial channel . 8.1.3 Multi-channel Side, additional channels . 8.2 Change of transmission rate during a
10、 session . 8.3 8.4 Further mode changes . 9 IS0 aggregation procedure Appendix I - Examples of procedures Appendix II - Example of SDL diagram for TAC initialisation . Appendix III - Comments on the modification of capsets and commands . 5.1 Intercommunication of non-audiovisual equipments - Case D
11、7.2 Channel synchronisation . 7.3 8 Recovery from fault conditions Page 1 1 1 1 2 3 4 4 4 5 5 8 9 10 12 12 12 12 12 12 13 13 13 13 15 15 16 16 16 16 17 17 18 18 18 18 19 23 24 Recommendation H.244 (07/95) 1 ITU-T RECflN*H.244 95 m 48b259L ObO83b9 158 m Recommendation H.244 SYNCHRONIZED AGGREGATION O
12、F MULTIPLE 64 OR 56 kbis CHANNELS (Geneva, 1995) 1 Scope This Recommendation provides for synchronisation and aggregation of multiple channels of 64 kbit/s or 56 kbivs, each being with or without octet integrity and relative transmission delay in the range f 1 second. It is applicable to a wide rang
13、e of user data transport up to 63 channels using ISO/IEC standard 13871, but special provision is made for audiovisual systems according to Recommendation H.221 i, up to 24 channels; the aggregation may be network-based or associated with Customer-Remises Equipment. The available operating modes (B
14、1, B2, B3, H2) provide options with/without transmission-management overhead and user-data rates aless-than the exact multiples of 64/56 kbids. The number of aggregated channels may be varied dynamically during a session. Procedures are given for dealing with faults, including loss of channels and s
15、lip. Call control is not covered in this Recommendation. 2 Normative references The following 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. Al
16、l Recommendations and other references are subject to revision; all 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 i
17、s regularly published. i IT Recommendation H.221 (1993), Frame structure for a 64 to 1920 kbit/s channel in audiovisual teleservices. 2 ITU Recommendation H.242 (1 993), System for establishing communication between audiovisual terminals using digital channels up to 2 Mbids. 3 ITU Recommendation H.3
18、20 (1993), Narrow-band visual telephone systems and terminal equipment. 4 ISO/IEC CD 13871, Digital Channel Aggregation. 5 ITU Recommendation H.230 (1 993, Frame-synchronous control and indication signalsfor audiovisual systems. 3 Definitions and symbols 3.1 Definitions For the purposes of this Reco
19、mmendation, the following definitions apply: 3.1.1 H.244 aggregation: Channel aggregation by the process described in clauses 7 and 8. 3.1.2 IS0 aggregation: Channel aggregation by the process described in 4. 3.1.3 single bidirectional digital connection. single channel equipment (SCE): A terminal o
20、r other unit (such as a LAN interface) having an interface for a 3.1.4 for multiple bidirectional digital connections at 64 kbit/s each. multiple channel equipment (MCE): A terminal or other unit (such as a LAN interface) having interface(s) Recommendation H.244 (07/95) 1 ITU-T RECMNxH-244 95 48b259
21、1 Ob08170 9T 3.1.5 channel aggregation unit (CAU): A device having both multiple 64 kbids accesses and a single access at a higher bit rate. Reference in this Recommendation to TAU or “aggregator” shall mean equipment conforming to this Recommendation. 3.1.6 in i. H.221 frame structure, H.221 framin
22、g: Frame structure according to Recommendation H.221, as set out 3.1.7 Capset: Abbreviation for “Capability set” - see 2. 3.1.8 Note 1.) user information: The application data streams passing (in both directions) between CAU and SCE. (See 3.1.9 calling end: The CAU or MCE which requests the first 64
23、/56-channel connection of the whole session, resulting in the establishment of the “initial channel”. If during fault-recovery procedures the intial channel is transferred to another connection, this does not affect the definition. (See Note 2.) 3.1.10 called end: The CAU or MCE which accepts the fi
24、rst 64/56-channel connection request of the whole session, resulting in the establishment of the “initial channel”. If during fault-recovery procedures the intial channel is transferred to another connection, this does not affect the definition. (See Note 2.) 3.1.11 clauses 7-8. TAC case: In-band co
25、mmunication between SCE and CAU takes place using H.221 BAS codes - see 3.1.12 NoTAC case: No in-band management communication between SCE and CAU takes place - the single channel is only a clear path for the data which will be wholly transmitted to the remote party; any communication between the te
26、rminal and the CAU is by means not specified in this Recommendation. 3.1.13 modes B1, B2, B3: Modes of aggregation by the method of 4 - see 5.2. 3.1.14 mode H2: Modes of aggregation by the method of clauses 7-8. 3.1.15 which is still in force. redundant command: A BAS command which repeats, unchange
27、d, a previously transmitted mode value 3.1.16 compatibility bits: Bit 8 of the first sixteen octets in every time-slot of a single channel except Time-slot 1. 3.1.17 determine the behaviour of a CAU as to choice of option or timing of its action. external setting: This term is used to express operat
28、ions outside the scope of this Recommendation which NOTES 1 2 In the audiovisual cases, the application data stream includes the H.221 frame structure. The significance of “calling” and “called” end-points is mentioned in 8.1.3. 3.2 Symbols NOTE - For readability, the capability and command values l
29、isted in References I and 5 are referred to in this Recommendation by their names rather than codepoint byte values; the use of name) for capabilities and name for commands serves to distinguish between these. N An integer, applied to 64/56-channels to define a parallel (un-aggregated) bitstream of
30、rate N x 64 kbits. n An integer, applied to 64 kbit/s to define a serial (or otherwise aggregated) bitstream of rate n*64 kbit/s. Na The number of active 64/56-channels between CAU and MCE or between two CAUS. Nm The maximum number of 64/56-channels which can be accepted by a CAU transmitting the va
31、lue IN,x BI. Nm Used to denote the incoming value of N, from the remote CAU, or equivalent from an MCE. 2 Recommendation H.244 (07/95) ITU-T RECMN*H.244 95 m i.1862593 Ob08373 806 m Nd The number of connections requested by the calling end, the lower of N, and Nm (N x 64k) Capabilities in the series
32、 IB), 2B), 3B corresponding to N = 1,2,3 . (applies to Mode H2 only). (n*64k) Capabilities in the series 64k, 128k, 192k) corresponding to n = 1,2,3 . nm Such that nm*64k is the highest transfer-rate capability incoming from the SCE for which the continuous series of rate capabilities (n, - 1)*64k,
33、(n, - 2)*64k), 2*64k is also present in the capset. N x 641 Multiplechannel commands defined in i. n*64k Single-channel commands defined in I. capex Command issued by a CAU (see 7.3.6.3) to an SCE to stimulate a capability exchange. AggIN* A double SBE symbol indicating the number n as determined by
34、 the process of 7.3.4.2; see the procedure described in clause 8 - see 5. null) Capability having no significance other than as a filler; only ever transmitted by a CAU, and therefore it identifies the capset as having last come from, or been forwarded by, a CAU; SCE must ignore any number of these
35、in an incoming capset - see I. SM-comp Capability to transmit and receive user information without using any compatibility bits, setting these to 1 -see i. SM-comp User information is not contained in the compatibility bits (and shall not be sent in the compatibility bits in the reverse direction ei
36、ther) - see i. S Audible signal (to be defined), which would be recognised by a human user as a call progress tone (he would not hang up). 4 Abbreviations For the purposes of the Recommendation, the following abbreviations are used: BAS CAU Channel Aggregation Unit FAS H.221 See 3.1 Bit-rate Allocat
37、ion Signal - see 11 Frame Alignment Signal - see i MC (side) Multiple Channel (side, of a CAU) MCE Multiple-Channel Equipment NCA, NIA, NIC, NID, NIS See 5 NoTAC No Terminal-Aggregator Communication SC (side) Single Channel (side, of a CAU) SCE Single-Channel Equipment SM-comp Single-Multiple compat
38、ibility TAC Terminal-Aggregator Communication UD Unspecified Data ITU-T RECMN*H-244 95 W 48b259L Ob08172 7Y2 ,. ., TAC 5 General CAU 5.1 Application of this Recommendation On the single-channel connections, which may be very short if the terminal and CAU are colocated, or much longer if a telecommun
39、ications link is involved, two options are provided for in this Recommendation: no in-band management communication on the single channel, this being only a clear path for the data which will be wholly transmitted to the remote party; any communication between the terminal and the CAU is by means no
40、t specified in this Recommendation; this is referred to as the “NoTAC” case - No Terminai-Aggregator Communication and applies when “IS0 aggregation” is used (see 4); in-band communication as specified in this Recommendation, using the BAS codes defined in 11 and the procedures of 2; this is referre
41、d to as the “TAC” case - Terminal-Aggregator Communication, and applies when “H.244 aggregation” is used (see clauses 7 and 8). 5.1.1 Intercommunication of Audiovisual equipments For audiovisual terminals conforming to 11 and 2. this Recommendation provides for synchronisation and aggregation of up
42、to 24 channels of 64 kbitfs or 56 kbitfs. each being with or without octet integrity and relative transmission delay in the range $: 1 second. Provision is made for the following intercommunication Cases A-C. 5.1.1.1 Case A For interconnection of a single-channel (SCE) and a multiple-channel audiovi
43、sual end-point (MCE), both conforming to 11 and 2, only H.244 aggregation is permissible (see Figure 1); this involves only one CAU, which may be within the network or close to the single-channel end-point. FIGURE 1M.244 5.1.1.2 Case B This case provides for interconnection between two single-channe
44、l audiovisual end-points which see the aggregated link purely as a clear data channel; each has a CAU associated with it, but there is no in-band control communication between the end-point and its associated CAU (see Figure 2); this is the NoTAC approach. The system is exactly the same as for unspe
45、cified data applications (see 5.1.2); the CAU-ISDN-CAU combination provides a clear channel at one of the transfer rates specified in l, and therefore shall use IS0 aggregation, Mode B1 or B3 (see 5.2). 4 Recommendation H.244 (07/95) CAU (NOTAC) FIGURE 2m.244 CAU (NoTAC) 5.1.13 CaseC ,. ., CAU TAC T
46、his provides for interconnection of two single-channel end-points both conforming to i and 2 and capable of the H.244 agregation operation described in clauses 7-8 (see Figure 3); this involves two CAUS, which may be within the network or close to the single-channel end-points. NOTE - It is not poss
47、ible to use TAC at one end and NoTAC at the other - see clause 6. , CAU .A TAC FIGURE 3m.244 5.1.2 Intercommunication of non-audiovisual equipments - Case D This Recommendation provides for synchronisation and aggregation of up to 63 channels of 64 kbit/s or 56 kbit/s, each being with or without oct
48、et integrity and relative transmission delay in the range * 1 second. It is applicable to a wide range of user information transport, including LAN-LAN interconnect, private circuit back-up, and other “unspecified data” applications. No in-band control communication takes place on the single-channel
49、 side. The equipments see the aggregated link purely as a clear data channel, and the structure or content of the data streams is of no concern to the aggregating equipment. IS0 aggregation is appropriate (see Figure 2); the CAU-ISDN-CAU combination provides a clear channel at one of the transfer rates specified in 4 using Mode B1, B2 or B3 (see 5.2). 5.2 Definition of the Modes of transmission on the MC side The four modes of transmission are defined below, the
