1、- ITU-T RECNN*G.765 APPENDIXJI 95 48b2591 Ob15290 875 = INTERNATIONAL TELECOMMUNICATION UNION ITU=T TELECOMMUNICATION STAN DARD IZATION SECTOR OF ITU Appendix I Rec. G.765 (1 1 /95) GENERAL ASPECTS OF DIGITAL TRANSMISSION SYSTEMS A GUIDE TO PCME Appendix I to ITU-T Recommendation G.765 (Previously “
2、CCITT Recommendation”) ITU-T RECMN+Gmb5 APPENDIXmI 95 H 48b2591 ObL529L 701 FOREWORD The IT-T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (ITU). The IT-T is responsible for studying technical, operating and tariff questions and issuing
3、 Recommen- dations on them with a view to standardizing telecommunications 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 th
4、ese topics. The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993). Appendix I to ITU-T Recommendation G.765 was prepared by ITU-T Study Group 15 (1993-1996) and was approved under the WTSC Resolution No
5、. 1 procedure on the 13th of November 1995. NOTE In this Appendix, the expression “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
6、in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the IT. . ITU-T RECHN*G.bS APPENDIXWI 95 m 4862571 Ob15292 648 I . 1 1.2 1.3 1.4 CONTENTS Terms and definitions . 1.1.1 I . 1.2 I . 1.3 I . 1.4 1.1.5 I . 1.6 1.1.7 I . 1.8
7、I . 1.9 1.1.10 1.1.11 1.1.12 1.1.13 1.1.14 1.1.15 1.1.16 1.1.17 1.1.18 1.1.19 I . 1.20 1.1.21 I . 1.22 I . 1.23 I . 1.24 I . 1.25 I . 1.26 1.1.27 I . 1.28 I . 1.29 I . 1.30 1.1.31 I . 1.32 block block dropping bursts . coding type (CT) field . core bits . data link connection identifier (DLCI) delay
8、 equalization (EQ) bit . digital circuit emulation (DICE) protocol . embedded adaptive differential pulse code modulation (ADPCM) block dropping indicator (BDI) digital speech interpolation . enhancement bits . errored second (ES) . frame relay gap . high level data link control (HDLC) protocol . ke
9、ep alive aim more (M) bit noise field originating endpoint packet header packet stream packetization interval scheduled play-out time terminating endpoint . unnumbered information (vi) frame . unnumbered information with header check (UIH) frame virtual data link capability (VDLC) protocol voice fra
10、me voice information field wideband packet network . time stamp (TS) . PCME tutorial . 1.2.1 Digital speech interpolation 1.2.2 Echo cancellation . 1.2.3 ADPCM coding of voiceband signais . 1.2.4 Facsimile demodulatiorremodulation 1.2.5 Packetization . 1.2.6 Frame relay and packet cross-connections
11、Performance 1.3.1 Congestion control 1.3.2 Traffic smoothing effects of block dropping 1.3.3 Performance of facsimile on IDR links . Planning and dimensioning . 1.4.1 General 1.4.2 PCME traffk engineering . 1.4.3 Bandwidth usage at various coding rates 1.4.4 Average bids vs . traffic load . 1.4.5 Bu
12、ild-out settings vs . traffic load Recommendation G.765 (11/95) Page 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 5 5 6 6 6 7 9 9 9 10 10 14 14 15 17 18 19 1 ITU-T RECMN*G-765 APPENDIX*I 95 = 4862593 0635293 584 1.5 Installation and acceptance . 1.5.1 A possible configuration ma
13、p for PCME 1.6.1 Point-to-point application . 1.6.2 Point-to-multipoint application . 1.6.3 Transient traffic applications I.6.4 Frame relay applications . 1.6.5 Mobile telephony applications 1.6 Examples of applications Page 22 22 23 23 23 23 25 27 Bibliography 33 11 Recommendation G.765 (1V95) App
14、endix I to Recommendation G.765 A GUIDE TO PCME (Geneva, 1995) (This appendix does not form an integral part of this Recommendation) 1.1 Terms and definitions This Recommendation uses the following terms that are not currently defined in Recommendation G.701. 1.1.1 block F: bloc S: bloque A block is
15、 a specific group of octets within a voice packet that is made of bits of the same significance. 1.1.2 block dropping F: abandon de blocs S: eliminacin de bloques Block dropping is a process by which one or more of the less significant blocks of a voice packet is dropped to alleviate congestion. 1.1
16、.3 block dropping indicator (BDI) F: indicateur dabandon de blocs S: indicator de eliminacin de bloques The Block Dropping Indicator (BDI) is the field of the voice packet header that indicates the number of blocks that have been dropped and the maximum number that can be dropped. 1.1.4 bursts F: sa
17、lves S: rfugas Bursts are periods of high energy content signals present in the access channel of a wideband network. 1.1.5 coding type (CT) field F: champ du type de codage S: campo de tipo de codificacin The coding type field of a voice/voiceband data packet is a 5-bit sequence in the packet heade
18、r that indicates the method of coding speech samples used at the originating endpoint before packetization. 1.1.6 core bits F: bits essentiels S: bits primarios The core bits form the subset of the total codeword of an embedded ADPCM coder that must reach the decoder. 1.1.7 data link connection iden
19、tifier (DLCI) F: identificateur de connexion de liaison de donnes S: identificador de conexin de enlace de datos The DLCI is a 13-bit field that defines the destination address of a frame on a physical-link-by-physical-link basis. Recommendation G.765 (1U95) 1 1TU-T RECMN*G=765 APPENDIXrI 95 4862573
20、 Ob35295 357 1.1.8 delay equalization (EQ) bit F: bit de compensation du dlai S: bit de igualacin de retardo The EQ bit is a parameter used to indicate to the terminating endpoint whether a packet should be built out or played out immediately to the channelized side. 1.1.9 digital circuit emulation
21、ICE) protocol F: protocole d?mulation de circuits numriques S: protocolo de emulacin de circuitos digitales The DICE protocol is a wideband protocol used to transport digital data that arrive on the channelized side through a specific format containing idle codes and repetition of user?s data. 1.1.1
22、0 digital speech interpolation F: interpolation numrique de la parole S: interpolacin digital de la palabra Digital speech interpolation is a process that takes advantage of inactive periods of a conversation to insert speech from other conversations and to remove silent periods. This is the same pr
23、ocess used for a G.763 DCF. 1.1.11 embedded adaptive differential pulse code modulation (ADPCM) F: modulation par impulsions et codage diffrentiel adaptatif imbriqu (MICDA) S: modulacin por impulsos codificados diferencial adaptable jerarquizada (MICDA) Embedded APCM algorithms are ADPCM algorithms
24、that quantize the difference between the input and the estimated signal into core bits and enhancement bits. 1.1.12 enhancement bits F: bits d?amlioration S: bits secundarios The enhancement bits in embedded ADPCM are bits that are not used in the prediction process in both the encoder and the decod
25、er. They enhance the coding performance when used in the decoding process by reducing the quantization noise in the reconstructed signal. 1.1.13 errored second (ES) F: seconde errone S: segundo con errores An errored second is a second during which one or more errors have occurred. 1.1.14 frame rela
26、y F: relayage de trame S: retransmisin de tramas Frame relay is a method of transporting HDLC frames within a network whereby the network nodes provide error detection without retransmission. Retransmissions are done at the endpoints of the network only. 1.1.15 gap F: pause S: pausa A gap is a perio
27、d of signals of low-energy contents present at a speech detection device. 2 Recommendation 6.765 (11/95) 1.1.16 high level data link control (HDLC) protocol F: protocole de commande de liaison de donnes haut niveau (HDLC) S: protocolo de control de enlace de datos de alto nivel (HDLC HDLC is a famil
28、y of bit-oriented, link-layer protocols defined by the International Organization for Standardization (ISO). 1.1.17 keep alive alarm F: alarme sur perte de rception de paquets S: alarma de prdida de paquetes A keep alive alarm is an alarm generated by a terminating endpoint that experiences loss of
29、keep alive packets. 1.1.18 more (M) bit F: bit de continuation . S: bit ms (M The M-bit is a bit used to indicate that more packets in sequence are to be expected by the terminating endpoint. 1.1.19 noise field F: champ de bruit S: campo de ruido The noise field is the field of the packet header tha
30、t indicates the level of background noise the terminating end may play out in the absence of packets. 1.1.20 originating endpoint F: extrmit dorigine S: punto extremo de origen The originating endpoint of a wideband packet node is the point that receives channelized traffic, packetizes it, and sends
31、 it into the wideband packet network. 1.1.21 packet header F: en-tte de paquet S: encabezamiento de paquete The G.764/G.765 packet header consists of Octets 4 to 8 (inclusive) of the frame (HDLC flags are excluded from the octet count). 1.1.22 packet stream F: train de paquets S: tren de paquetes A
32、packet stream is a collection of logical links multiplexed together onto one physical channel between two endpoints of the wideband packet network. 1.1.23 packetization interval F: intervalle de mise en paquets S: intervalo de empaquetado The packetization interval is the duration of the channelized
33、 traffic that has been packetized. 1.1.24 scheduled play-out time F: horaire de restitution S: horario de restitucidn The scheduled play-out time is the time at which a received packet is to be played out. Recommendation G.765 (1l95) 3 ITU-T RECMN*G-7b5 APPENDIXrI 95 4862593 Ob15297 l12T 1.1.25 term
34、inating endpoint F: extrmit de signalisation S: punto extremo de terminacin The terminating endpoint of a wideband packet node is the part of the node that receives packetized traffic, depacketizes it, and then plays it back as channelized traffk. 1.1.26 time stamp (TS) F: horodateur S: indicacin de
35、 tiempo The time stamp is a field that records the cumulative variable queueing delay experienced by packet in transversing the network with a resolution of 1 ms. 1.1.27 unnumbered information (Vi) frame F: trame dinformation non numrote S: trama de informacin no numerada (VI) A u1 frame is a frame
36、used to transfer unacknowledged information between two link-layer entities. The format and encoding are the same as specified in Recommendation 4.92 1 1 1.441. The CRC is derived over the entire frame. 1.1.28 unnumbered information with header check (UIH) frame F: trame dinformation non numrote ave
37、c vrification den-tte S: trama de informacin no numerada con verificacin de encabezamiento (UIH) The UM frame is similar to the UI frame except that the CRC sequence is derived over selected bits of the frame and not the whole frame. In Recommendation G.764, the CRC calculation is over the frame and
38、 packet headers (the first 8 octets excluding flags). 1.1.29 virtual data link capability (VDLC) protocol F: protocole de capacit de liaison virtuelle de donnes S: protocolo de capacidad de enlace de datos virtual The VDLC protocol is a wideband protocol that is used to transport digital data packet
39、s arriving from the channelized side in HDLC frames. 1.1.30 voice frame F: trame de parole S: trama de VOZ The voice frame is a G.764 UIH frame that contains a voice packet in its information field. 1.1.31 voice information field F. champ dinformation de la parole S: campo de informacin de voz The v
40、oice infomation field is the field that contains blocks of voice traffic. 1.1.32 wideband packet network F: rseau de paquets large bande S: red de paquetes de banda ancha A wideband packet network is a packet network that offers transmission channels capable of supporting rates above 64 kbit/s and b
41、elow the broadband rate of 150 Mbit/s. 4 Recommendation G.765 (11/95) ITU-T RECMN*G.765 APPENDIXxI 95 48b259L 06L5298 Ob6 H 1.2 PCME tutorial A Packet Circuit Multiplication Equipment (PCME) uses several strands of technology. These strands can be divided into two categories. The first category cons
42、ists of technologies common to other Digital Circuit Multiplication Equipment (DCME), such as digital speech interpolation, echo cancellation, speech compression, and facsimile demodulation. It should be noted, however, that for these common techniques, PCME may offer additional features, such as em
43、bedded coding of speech, which can be useful in congestion control. The second category comprises technologies unique to PCME, such as packetization and frame relay. A network operator can utilize the PCME to make several types of connections simultaneously (within the constraints of the capacity of
44、 the system). The operator defines how the PCME is configured for each type. A typical connection involves the compression and packetization of voiceband traffic (voice or data). Other connections may include 64 kbils uncompressed channels that can be cross-connected as well. It is also possible to
45、cross-connect streams of packets at each point of the network; this allows a PCME to operate within frame relay networks as well. The following is a brief description of these technology strands. 1.2.1 Digital speech interpolation Conversational speech is not continuous and rarely uses both directio
46、ns of transmission simultaneously. Digital Speech Interpolation (DSI) takes advantage of inactive periods in a conversation to insert speech from other conversations. Because speech activity occupies, on the average, about 40 percent of the total time in a conversation, reduction of the bit rate nee
47、ded for voice can be done by removing all idle periods, that is, removing silent intervals from speech or by coding the silence at a lower bit rate than that used for speech. Time Assignment Speech Interpolation (TASI) was originally used for undersea analogue cable systems then transposed to digita
48、l satellite transmission systems. Later on, digital speech interpolation was combined with variable rate ADPCM coding (see 1.2.3) to increase the efficient use of the transmission path. To recognize that speech is being transmitted, a highly sensitive speech detector is required. The quality of the
49、speech detector at the originating end is one of the important factors that determines the overall quality of the speech. If the speech detector does not detect speech correctly, it could chop the words beginning (ftdnt-end clipping), thereby causing severe degradation to the speech quality. In contrast, if the speech detector is too sensitive, then more silence intervals will be passed and the gain will be reduced. Usually, the speech detector extends the effective duration of the speech burst, an interval denoted as
