1、INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU E.528 (02/96) TELEPHONE NETWORK AND ISDN QUALITY OF SERVICE, NETWORK MANAGEMENT AND TRAFFIC ENGINEERING DIMENSIONING OF DIGITAL CIRCUIT MULTIPLICATION EQUIPMENT (DCME) SYSTEMS ITU-T Recommendation E.528 (Prev
2、iously “CCITT Recommendation” FOREWORD The ITU-T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (ITU). The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommen- dations on them with a view to st
3、andardizing 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 these topics. The approval of Recommendations
4、by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993). ITU-T Recommendation ES28 was prepared by ITU-T Study Group 2 (1993-1996) and was approved under the WTSC Resolution No. 1 procedure on the 19th of February 1996. NOTE In this Rec
5、ommendation, 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 in any form or by any means, electronic or mechanical,
6、 including photocopying and microfilm, without permission in writing from the ITU. STDmITU-T RECMN E.528-ENGL 177b m qBb2591 Ob23287 177 m CONTENTS 1 Scope 2 References 3 Definitions 4 Abbreviations . 5 Dimensioning elements Determining Quality of Service (QOS) and Grade of Service (GOS) parameters
7、. General principles of dimensioning method . Parameters relevant to dimensioning calculations 5.3.1 General parameters . ADPCM mode for low rate encoding . DCME gain for Voice G, . 5.1 5.2 5.3 5.3.2 5.3.3 Digital speech interpolation 5.4 DCME gain determination (in accordance with Recommendation G.
8、766) 5.4.1 Method for dimensioning of DCME links and gain computation Determination of the number of DCME links 7.1 Determination of blocking probabilities for point-to-point DCME links . Annex A Effects of specially chosen parameters on DCME dimensioning . 6 7 7.2 Multiple system configuration A .
9、1 A.2 An example of DCME dimensioning calculation . Annex B . Appendix I . 1.1 1.3 1.4 Dynamic Load Control (DLC) functionality 1.2 Maximum achievable G, Maximum allowable percentage of VBD calls . Determination of the blocking probabilities for dimensioning of point-to-point links that include DCME
10、 . 1.4.1 DLC activation and deactivation . 1.4.2 Bearer channel loading conditions References . Appendix II Page 1 1 2 2 3 3 3 3 3 4 4 4 4 5 5 5 6 6 6 10 12 12 12 12 13 13 13 14 14 15 Recommendation ES28 (02/96) i STD*ITU-T RECMN E-528-ENGL L77b 48b259L Ob23270 797 M SUMMARY Digital Circuit Multipli
11、cation Equipment (DCME) allows a high degree of utilization of digital circuits in Public Switched Telephone Networks (PSTN) and Integrated Services Digital Networks (ISDN) providing integration of traffic containing voice, Voice Band Data (VBD) and the facsimile portion of Voice Band Data (VBD) tra
12、ffic. Dimensioning method for DCME system, described in this Recommendation, deals with a group of trunks (circuit group, as defined in Recommendation E.600) between two switches, where DCMEs are used to achieve a statistical multiplexing gain. This Recommendation also describes the GOS parameters t
13、hat play a part in the DCME gain calculation. This Recommendation deals with a point-to-point DCME single clique operation configuration. Dimensioning of complex multiclique/multidestination types of DCME systems is for further study. 11 Recommendation ES28 (OZ96) Recommendation ES28 DIMENSIONING OF
14、 DIGITAL CIRCUIT MULTIPLICATION EQUIPMENT (DCME) SYSTEMS (Geneva, 1996) 1 Scope Digital Circuit Multiplication Equipment (DCME) allows a high degree of utilization of digital circuits in hblic Switched Telephone Networks (PSTN) and Integrated Services Digital Networks (ISDN) providing integration of
15、 traffic containing voice, Voice Band Data (VBD) and the facsimile portion of Voice Band Data (VBD) traffic. Dimensioning method for DCME system, described in this Recommendation, deals with a group of trunks (circuit group, as defined in Recommendation E.600) between two switches, where DCMEs are u
16、sed to achieve a statistical multiplexing gain. The purpose of the dimensioning method is to determine the size of the group of trunks, the number and properties of the DCME output (bearer) channels and the number of DCMEs for specific traffic mixes - voice, VBD and facsimile to provide a satisfacto
17、ry Grade of Service (GOS) cost-effectively. Further, this Recommendation also describes the GOS parameters that play a part in the DCME gain calculation. The DCME gain is described in this Recommendation as a ratio of a number of trunk channels to a number of available bearer channels and is used to
18、 determine availability and specific properties of the DCME bearer channels. This Recommendation deals with a point-to-point DCME single clique operation configuration. Dimensioning of complex multicliquelmultidestination types of DCME systems is for further study. 2 References The following Recomme
19、ndations 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. All Recommendations and other references are subject to revision: all users of this Recommendation are
20、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 is regularly published. - CCIT Recommendation G.766 (1992), Facsimile demodulatiodremodulation for dig
21、ital circuit multiplication equipment. - IT-T Recommendation G.763 (1994), Digital circuit multiplication equipment using ADPCM (Recommendation G. 726) and digital speech interpolation. - CCITT Recommendation G.726 (1990), 40/32/24/16 kbitls Adaptive Differential Pulse Code Modulation (ADPCM). - ITU
22、-T Recommendation E.301 (1993), Impact of non-voice applications on the telephone network. - CCITT Recommendation ES20 (1988), Number of circuits to be provided in automatic ador semi- automatic operation, without ovelflow facilities. - CCITT Recommendation E.721 (1991), Network grade of service par
23、ameters and target values for circuit-switched services in the evolving ISDN. - ITU-T Recommendation P.84 (1993), Subjective listening test method for evaluating digital circuit multiplication and packeted voice systems. - ITU-T Recommendation Q.50 (1993), Signalling between Circuit Multiplication E
24、quipment (CME) and International Switching Centres (ISC). Recommendation ES28 (OY96) 1 STD-ITU-T RECMN E.528-ENGL l97b q8b257L Ob23272 7bl 3 Definitions The following terms and definitions applicable to DCME are described in clause 21G.763. Definitions relating to DCME: These definitions are used th
25、roughout the texts of this Recommendation. 3.1 3.2 Bearer Channel (BC) Average Encoding Rate - Average number of Bits per Sample (bithampie) (ABS) 3.3 Trunk Channel (TC) 3.4 Clique 3.5 DCME gain 3.6 Digital Speech Interpolation (DSI) gain 3.7 Facsimile demodulationhemodulation 3.8 Freezeout 3.9 Free
26、zeout fraction 3.10 Low Rate Encoding (LRE) gain 3.11 Speech Activity Factor (AF) 3.12 Variable Bit Rate (VBR) The following definitions are specific to DCME dimensioning as described in this Recommendation. 3.13 clipping: Clipping is an alteration of the front-end of a speech burst due to lack of s
27、ufficient time for processing. Occurs in most cases as a result of speech detectors processing functions employed by DSI systems when detectors try to process a front of a speech burst but lack the sufficient time to operate. Competitive clipping is the impairment caused by the overload control stra
28、tegy which allows freezeout to occur when bearer channels are temporarily unavailable. 3.14 tion (DSI) gain factors. 3.15 each direction. DCME gain for voice G,: G, is the product of Low Rate Encoding (LRE) and Digital Speech Interpola- DCME link: A number of bearer channels between two DCMEs transm
29、itting concentrated information in 3.16 nibble: Nibble is the term which refers to a 4-bit/sample-coded channel and corresponds to a data rate of 32 kbivs. It is always associated with the capacity of a bearer channel. The term full bearer channel refers to a channel consisting of 61 nibbles, with t
30、he exception of the Time Slot zero and a single nibble used for Assignment Message Channel (AMC). 3.17 rate of 64 kbivs. It is also used to refer to a trunk channel. time slot (TS): Time Slot is the term which refers to an 8-bit/sample-coded channel and corresponds to data 3.18 point-to-point mode:
31、A DCME operational mode in which the traffic is exchanged between two correspond- ing DCMEs and the trunk channel traffic is interpolated over available bearer channels for only one destination in each direction. 4 Abbreviations For the purposes of this Recommendation, the following abbreviations ar
32、e used: ABS Average Bits per Sample ADPCM Adaptive Differential Pulse Code Modulation AF Activity Factor 2 Recommendation ES28 (02/96) STD-ITU-T RECMN E.528-ENGL L79b 48b259L Ob23293 bT8 CME DCME DLC DSI FEC G3 GOS G“ ISDN LE PSTN QOS VBD Circuit Multiplication Equipment Digital Circuit Multiplicati
33、on Equipment Dynamic Load Control Digital Speech Interpolation Forward Error Correction Group 3 FAX Grade of Service Gain for Voice Integrated Services Digital Network Low Rate Encoding Public Switched Telephone Network Quality of Service Voice Band Data 5 Dimensioning elements 5.1 The traffic offer
34、ed to networks containing DCME is determined in accordance with methods specified in the E.500-Series of Recommendations. Determination of a DCME gain, as a prerequisite for DCME dimensioning, for the overall composite traffic load requires distinction (in accordance with Recommendation E.301) among
35、 and between voice, VBD (non-facsimile and facsimile). Determination of GOS and QOS should provide an initial input for dimensioning of DCME systems; in the ISDN case Recommendation E.721 should provide the necessary guidance in respect to GOS parameters. The following parameters are considered for
36、dimensioning of DCME systems: Determining Quality of Service (QOS) and Grade of Service (GOS) parameters - QOS: 0 level of the front-end clipping; a tolerated number of bit per sample used for speech encoding. - GOS: call blocking probability. 5.2 The following principles are observed in the DCME di
37、mensioning method described in this Recommendation: General principles of dimensioning method A single link of point-to-point DCME is dimensioned by calculating DCh4E gain for voice, the number of necessary nibbles (size of bearer channel) and DCME gain for assumed trunk capacity and traffic mix. Th
38、en, the necessary number of DCME links for the given trunk group is determined, to meet the required call blocking probability objectives. 5.3 Parameters relevant to dimensioning calculations 5.3.1 General parameters 0 0 A number of trunk channels versus a number of bearer channels. Trunk channel oc
39、cupancy and speech activity. It is usual to assume a 35% to 40% of speech activity depending on the type of a language. Outside of the route busy hour occupancy of the trunk channels is lower than in the busy hour. This dictates a reduction of the Speech Activity Factor to about 27% outside the busy
40、 hour to allow the maximum of 40% during the busy hour. Recommendation ES28 (OU96) 3 VBD traffic. A factor to be considered is a percentage of the VBD traffic that may vary depending upon the route and time of day. Ratio of half-to-full duplex VBD. 0 Signalling between DCMEs may hold channels active
41、. for significant periods not allowing any interpolation during the signalling processing periods. 64 kbiils clear channel traffic. A significant factor is a required number of 64 kbit/s clear channels, each absorbing two 32 kbiils bearer channels. Minimum acceptable speech quality. It is determined
42、 by the encoding rate of the LE process and by the amount of speech lost while newly active trunk channels are being connected to bearer channels. If a large number of these channels are in competition, the beginning of a speech burst is more likely to be clipped; if relatively few trunk channels ar
43、e active, a part of a speech burst could be frozen. 5.3.2 ADPCM mode for Low Rate Encoding The ADPCM method is assumed to be used for coding speech with bit rates less than 64 kbitfs (e.g. the 32 kbiils). This technique is commonly used in DCME to increase the circuit capacity. The ADPCM increases t
44、he channel occupancy by means of encoding at a lower number of bit per sample than the PCM. An ordinary PCM encodes a voice channel at 64 kbiils using a rate of 8-biilsample encoding. The ADPCM coding takes into account the nature of a signal, and is capable of reducing the encoding rate: 5-bit/samp
45、le for VBD signals at 40 kbids data rate; 0 4-biilsample for a regular voice signal at 32 kbiils data rate; 3- or 2-bidsample for an overload-voice signal, corresponding to 24 kbiils and 16 kbiils data rates. Compressing the signai by the ADPCM in this manner could double the channel capacity. 5.3.3
46、 Digital Speech Interpolation The DSI method is assumed to be used for speech processing. This technique minimizes inactive periods during a conversation, creating extra channel occupancy. The gain based on the DSI processing is defined as the ratio of a number of voice channels over a number of bea
47、rer nibbles (4-bit segments) required to accommodate the voice channels with a given (user determined) level of speech quality. Typically a gain of up to 3: 1 (minimum of 2: 1) could be produced by the DSI processing for the speech activity of 30% to 40%. Interpolated voice channels are assigned to
48、available bearer channels. If a bearer capacity is not available when a voice channel becomes active, front-end clipping of the voice spurt occurs. Overload bearer channels are created to reduce the clipping probability during the peak traffic conditions. This in turn requires reduction of the ADPCM
49、 encoding rate for voice channels from normal 4-biilsample to a lower value; typically, greater or equal to 3-biilsample of 3/4-bit overload condition and greater or equal to 2-bit/sample for 2/3-bit overload condition. 5.4 DCME gain determination (in accordance with Recommendation 6.766) 5.4.1 DCME gain for voice G, Equations for G, calculation provided in Annex B are quoted from Recommendation G.763. The formulae used for the G, calculation are empirical; they are the result of more formal mathematical analysis based on the statistical model of DCME that takes into account the
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