1、INTERNATIONAL TELECOMMUNICATION UNIONITU-TG.768TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU(03/2001)SERIES G: TRANSMISSION SYSTEMS AND MEDIA,DIGITAL SYSTEMS AND NETWORKSDigital terminal equipments Principal characteristics oftranscoder and digital multiplication equipmentDigital circuit multiplicat
2、ion equipment using 8kbit/s CS-ACELPCAUTION !PREPUBLISHED RECOMMENDATIONThis prepublication is an unedited version of a recently approved Recommendation.It will be replaced by the published version after editing. Therefore, there will bedifferences between this prepublication and the published versi
3、on.FOREWORDThe International Telecommunication Union (ITU) is the United Nations specialized agency in the field of tele-communications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU.ITU-T is responsible for studying technical, operating and tariff questions an
4、d issuing Recommendations onthem with a view to standardizing telecommunications on a worldwide basis.The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishesthe topics for study by the ITU-T study groups which, in turn, produce Recommendations on these
5、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 areprepared on a collaborative basis with ISO and IEC.NOTEIn this Recommendation, the expression “
6、Administration“ is used for conciseness to indicate both atelecommunication administration and a recognized operating agency.INTELLECTUAL PROPERTY RIGHTSITU draws attention to the possibility that the practice or implementation of this Recommendation may involvethe use of a claimed Intellectual Prop
7、erty Right. ITU takes no position concerning the evidence, validity orapplicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of theRecommendation development process.As of the date of approval of this Recommendation, ITU had/had not received notice o
8、f intellectual property,protected by patents, which may be required to implement this Recommendation. However, implementors arecautioned that this may not represent the latest information and are therefore strongly urged to consult the TSBpatent database. ITU 2001All rights reserved. No part of this
9、 publication may be reproduced or utilized in any form or by any means,electronic or mechanical, including photocopying and microfilm, without permission in writing from ITU.ITU-T G.768 (03/2001) Prepublished version 1Recommendation G.768DIGITAL CIRCUIT MULTIPLICATION EQUIPMENT USING 8 KBIT/S CS-ACE
10、LP(Geneva, 2001)SummaryThis Recommendation specifies the elements of DCME using 8 kbit/s CS-ACELP, Digital SpeechInterpolation (DSI) and Facsimile Demodulation/Remodulation in order to achieve interworking ofsuch equipment. It specifies extensions and deviations for Recommendations G.763, G.766 and
11、G.767which specify a 32 kbit/s ADPCM DCME, and Facsimile Demodulation/Remodulation and 16 kbit/sLD-CELP DCME respectively.1 ScopeThis Recommendation specifies the elements of DCME using 8 kbit/s CS-ACELP, Digital SpeechInterpolation (DSI) and facsimile demodulation/remodulation in order to achieve i
12、nterworking of suchequipment. It is an extension to ITU-T Recommendations G.763 (Digital Circuit MultiplicationEquipment Using 32 kbit/s ADPCM and Digital Speech Interpolation) and G.766 (FacsimileDemodulation/Remodulation for DCME), as it specifies the deviations of the 8 kbit/s DCME from theG.763.
13、2 ReferenceThe following ITU-T Recommendations and other references contain provisions which, throughreference in this text, constitute provisions of this Recommendation. At the time of publication, theeditions indicated were valid. All Recommendations and other references are subject to revision; a
14、llusers of this Recommendation are therefore encouraged to investigate the possibility of applying themost recent edition of the Recommendations and other references listed below. A list of the currentlyvalid ITU-T Recommendations is regularly published. ITU-T Recommendation G.726, (12/90) - 40, 32,
15、 24, 16 kbit/s Adaptive Differential PulseCode Modulation (ADPCM) Annex J (09/99) to ITU-T Recommendation G.728 - Variable bit-rate operation of LD-CELPmainly for voiceband-data applications in DCME ITU-T Recommendation G.729 (03/96) - C source code and test vectors for implementationverification of
16、 the G.729 8 kbit/s CS-ACELP speech coder Annex D to (09/98) to ITU-T Recommendation G.729 - Coding of speech at 8 kbit/s usingConjugate Structure Algebraic-Code-Excited Linear-Prediction (CS-ACELP) Annex D: 6.4kbit/s CS-ACELP speech coding algorithm ITU-T Recommendation G.763 (1998), Digital circui
17、t multiplication equipment usingADPCM (Recommendation G.726) and digital speech interpolation. ITU-T Recommendation G.766 (1996), Facsimile demodulation/remodulation for digitalcircuit multiplication equipment.ITU-T G.768 (03/2001) Prepublished version 2 ITU-T Recommendation G.767 (10/98) - Digital
18、circuit multiplication equipment using16kbit/s LD-CELP, digital speech interpolation and facsimile demodulation/remodulation3 Terms and DefinitionsIn addition to the terms and definitions of ITU-T Recommendations G.763 and G.766, the followinglist is used in this Recommendation:3.1 Basic Control Cha
19、nnel (BCC)A DCME Control Channel used for a pool with IT numbers less than or equal to 240. It canaccommodate four assignment messages/frame.3.2 Expanded Control ChannelA DCME Control Channel used for a pool with IT numbers more than 240. It can accommodate eightassignment messages/frame.4 Abbreviat
20、ionsIn addition to the abbreviations and acronyms of ITU-T Recommendations G.763 and G.766, thefollowing list is used in this Recommendation:BCC Basic Control ChannelECC Expanded Control Channel5 DCME Frame Structure5.1 General5.1.1 Supported ServicesThe 8 kbit/s DCME frame structure accommodates th
21、e following services: 8 bit channels to support 64 kbit/s transparent of VBD calls, 1 bit channels to support voice calls at CS-ACELP 8 kbit/s and 6.4 kbit/s according to ITU-TRecommendation G.729 and its Annex D, 2 bit channels to support SS No. 5 Tone Signals at 16 kbit/s according to ITU-T Recomm
22、endationG.726, 5 bit channels to support VBD calls at 40 kbit/s according to ITU-T Recommendation G.728 andits Annex J, 4 bit channels to support fax banks carrying demodulated fax calls in the same manner as in ITU-TRecommendations G.763 and G.766, 4 bit channels to support bit banks carrying the f
23、ifth bits of 40 kbit/s channels for non-demodulatedfax calls and voice band data calls, 8, 5 and 1 bit channels to support 64 kbit/s, 40 kbit/s, 8 kbit/s, and 6.4 kbits preassigned channels.ITU-T G.768 (03/2001) Prepublished version 35.1.2 PCM FrameAs in G.763, the bearer structure of the 8 kbit/s D
24、CME retains compatibility with ITU-TRecommendation G.704, so it contains 24 or 32 consecutively numbered 8 bit time slots, from 1 to 24,for a 1544 kbit/s facility, or from 0 to 31, for a 2048 kbit/s facility.5.1.3 DCME Frame and Sub-FrameThe low rate encoding algorithm used for speech signals in the
25、 8 kbit/s DCME is CS-ACELP speechencoding algorithm conforming to ITU-T Recommendation G.729 and its Annex D. The CS-ACELPalgorithm has 10 ms of coding frame period, and consequently, the frame period of 8kbit/s DCME is10 ms.ndles5.1.4 DCME MultiframeThe IT related circuit supervision/alarm conditio
26、n field of the asynchronous word supports up to620 ITs, carried over up to 20 primary rate interfaces. The G.768 DCME multiframe of 18 DCMEframes is used to accommodate that.5.1.5 Relationship between the FramesA DCME Frame, having is composed of four DCME Sub frames having sub frame period of 2.5 m
27、s,and each DCME Sub Frame is composed of 20 PCM Frames. A DCME Multi Frame is composed of18 DCME Frames. Figure 1/G.768 shows the relationship between DCME Multiframe, DCME Frame,DCME Sub-frame and PCM Frame.Figure 1/G.768 Relationship between Associated Frames and Multi FramesDCMEMulti frame #1DCME
28、Multi frame #2DCMEMulti frame #nDCMEFrame # 0DCMEFrame #1DCMEFrame #17DCMESub-frame #0DCMESub-frame #1DCMESub-frame #3PCMFrame #0PCMFrame #2PCMFrame #19TS 0TS 1TS 31ITU-T G.768 (03/2001) Prepublished version 46 Trunk Interface Structure6.1 Type of Trunk InterfaceTrunk interface shall be either E1 or
29、 T1 PRI.6.2 Number of Trunk Interfaces, Trunk ChannelsUp to 20 E1 or T1 interfaces shall be supported by DCME. The maximum number of ITs shall be 620.6.3 Type of Trunk ChannelsThe type of Trunk channels shall be 64 kbit/s A-law or -law.7 Bearer Interface Structure7.1 Cliques, Destinations and Bearer
30、s7.1.1 Number of CliquesThe total number of cliques (pools) available over the 2 bearers shall be 4. Each pool starts and endson TS boundaries (and therefore occupies an integral number of time slots); any single clique shall notbe split into different physical interfaces and, consequently, shall no
31、t exceed the maximum bearercapacity of 31 time slots.7.1.2 Number of DestinationsThe maximum number of destinations is 4 including the cases of mixed operation between multi-clique and multi-destination modes.7.1.3 Multiple outgoing BearersOptionally the equipment can support a maximum of 2 outgoing
32、 bearer facilities. A single bearerfacility may be able to carry up to 4 cliques, so if a single bearer carries the maximum of 4 cliques,there is no option for a second bearer. The purpose of supporting two outgoing bearer facilitiesis toutilize the outgoing bearer facilities more efficiently. The D
33、CME is supporting Multidestinationoperation with up to 4 destinations and consequently four incoming bearer facilities become necessary,whereas one outgoing facility is enough to send out signals resulting three outgoing bearer facilities arenot in use in typical hardware implementation.The basic ph
34、ilosophy to support two outgoing bearer is to make more efficient use of hardware resources, withthe potential sacrifice of compression gain.One possibility is to dismiss the necessity of external cross-connect facility at bearer side. The outgoing bearerchannel pools can be assigned to different ou
35、tgoing facilities.Another possibility is to make use more bearer channels to accommodate the traffics including voiceband datasignals. Using two outgoing bearer facilities can enables the full use of ITs even in the case a high compressiongain can not be expected because of the existence of VBD call
36、s.In this context, using two outgoing bearer facilities does not imply the duplication of DCME capacity. Thefundamental design of 8 kbit/s DCME shall be based on the usage of single outgoing bearer.7.2 Assignment MessageFollowings are the list of assignment messages to be processed in G.768 DCME. Th
37、e number impliestheir priorities to be processed at transmission unit. Compared with G.763 DCME and G.767 DCME,ITU-T G.768 (03/2001) Prepublished version 51. Dummy message2. Signalling message via through USM3. On-demand 64 kb/s Channel disconnection message4. Fax-bank disconnection message5. Overlo
38、ad BC disconnection message6. On-demand 64 kb/s Channel connection message7. Fax-bank release message8. Data Connection message9. Speech Connection message10. Channel Check Test disconnection message11. Refreshment messageCompared with conventional G.763 DCME and G.767 DCME, 10thmessage for Channel
39、Check Testdisconnection is added. The reason to add this new message is to avoid CCT sequence to stay on the same BCin case the channel activity is rather low.The details of the procedure for generating Channel Check Test disconnection message is as follows;When CCT signal connected to a BC becomes
40、inactive, the connection shall be disconnected. Thetransmit unit shall execute disconnection procedure and send out an assignment message beingcomposed of corresponding BC number and the Synchronous data word of “0000”. On receiving thismessage, the receive unit shall disconnect corresponding BC and
41、 the special test port. Associated BC,encoder and decoder shall become free.7.3 Bearer Channels (BC)8 kbit/s CS-ACELP encoded voice calls nominally use 1 bits every PCM frame. Therefore the 8 kbit/sDCME bearer channels occupy 1 bit each. These basic Bearer Channels (BCs) shall occupies 80 bitsevery
42、DCME frame.7.4 Control Channel (CC)The Basic Control Channel (BCC) of the 8 kbit/s DCME occupies 4 bits every PCM frame, i.e. 2 QBs.BCC holds the synchronization word, four assignment message (IT and BC numbers and synchronousdata word), the asynchronous data word and some error correction bits in e
43、very DCME frame. BCCshall be applied to the pool with ITs less than or equal to 240 channels.If the number of ITs exceeds 240 channels on specific pool, an Expanded Control Channel (ECC) shallbe used for the pool. ECC occupies 6 bits every PCM frame, i.e. 3 QBs, and holds the synchronizationword, ei
44、ght assignment message (IT and BC numbers and synchronous data word), the asynchronousdata words and some error correction bits in every DCME frame.7.5 BC numbering and the use of the bearer frameEach time slot is subdivided into 1-bit slots. The leftmost two or three QBs (four or six 1-bit slots) o
45、feach pool carries the control channel (BCC or ECC, respectively). The remaining 1-bit slots of thepool are the Bearer Channels (BCs) and are used to carry traffic.The normal range BCs are consecutively numbered. When BCC is used, the BC that follows thecontrol channel is BC number one. In the case
46、of ECC, the numbering starts with 3, i.e. BC number 1ITU-T G.768 (03/2001) Prepublished version 6and 2 are skipped. In the case of a single pool, the maximum number of normal BCs is 244 for BCCcase and 242 for ECC case. The numbering scheme is shown in Figure 2/G.768.1Figure 2/G.768 Example of DCME
47、frame structure7.5.1 8-bit (64 kbit/s transparent calls) BCsThe BC number in the assignment message indicates the BC which carries the first bit of the 8-bitsample (MSB). The rest of the bits are carried by the next seven higher BCs. The same restrictions ofG.763 are maintained, so unrestricted 64 k
48、bit/s ITs will occupy one G.704 time slot. 8 kbit/s DCMEshall maintain frame integrity of consecutive trunk time slots which are allocated for N 64 kbit/scalls.7.5.2 5-bit (VBD optimized 40 kbit/s LD-CELP) BCsThe BC number in the assignment message indicates the BC which carries the first bit (MSB)
49、of the 5-bit sample. The next higher BC carries the next bits (MSB 1) and so on. The 5thbit (LSB) is obtainedfrom a different 4-bit bearer channel which is independently assigned as a bit bank. Similarly toRecommendation G.763, all 4-bit BCs (Data, FB or BB) occupy either the four MSBs or the four LSBsof a G.704 time slot. This implies that the BC number in the assignment message, for such BCs, can beexpressed as;14 + n (n= 0, 1, 2, 3)7.5.3 4-bit BCs (Bit bank, Fax bank)8 kbit/s DCME fax banks and bit banks are used in the same manner as they are used in
