1、INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU Series G Supplement 38 (1 0/98) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Variable bit rate calculations for ITU-T Recommendation G.767 Digital Circuit Multiplication Equipment (D
2、CME) Supplement 38 to ITU-T G-series Recommendations (Previously CCITT Recommendation) STD-ITU-T RECMN SERIES G SUPP 38-ENGL I998 llb259L Ub548b 5ll5 W ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS INTERNA
3、TIONAL ANALOGUE CARRIER SYSTEM GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER- TRANSM ISS1 ON SYSTEMS G. 100-G.199 G.200-G.299 INDIVIDUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE G. 300-G. 399 SYSTEMS ON METALLIC LINES GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE WITH
4、 METALLIC LINES G.400-G.449 SYSTEMS ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY G.450-G.499 TESTING EQUIPMENTS TRANSMISSION MEDIA CHARACTERISTICS G.600-G.699 DIGITAL TRANSMISSION SYSTEMS TERMINAL EQUIPMENTS G.700-G.799 DIGITAL NETWORKS G. 8
5、00-G. 899 DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G .900-G.999 For further details, please refer to ITU-T List of Recommendations, - - - STD-ITU-T RECMN SERIES G SUPP 38-ENGL 1998 4862591 0654887 481 m SUPPLEMENT 38 TO ITU-T G-SERIES RECOMMENDATIONS VARIABLE BIT RATE CALCULATIONS FOR ITU-T RECOMMEN
6、DATION G.767 DIGITAL CIRCUIT MULTIPLICATION EQUIPMENT (DCME) I l Seurce I Supplement 38 to ITU-T G-series Recommendations, was prepared by ITU-T Study Group 15 (1997-2000) and was approved under the WTSC Resolution No. 5 procedure on the 13“ of October 1998. G series - Supplement 38 (10/98) 1 _ -_-
7、- sTD.1TU-T RECMN SERIES G SUPP 38-ENGL 1778 Yb2571 Ob54888 318 M FOREWORD ITU (International Telecommunication Union) is the United Nations Specialized Agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the ITU. The ITU-T is r
8、esponsible for studying technical, operating and tariff questions and issuing Recommendations 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
9、 the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1. In some areas of information technology which fall within ITU-Ts purview, the necessary s
10、tandards are prepared on a collaborative basis with IS0 and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. INTELLECTUAL PROPERTY RIGHTS The ITU draws attention to the pos
11、sibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. The ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of
12、 the Recommendation development process. As of the date of approval of this Recommendation, the ITU hadhad not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the l
13、atest information and are therefore strongly urged to consult the TSB patent database. O IT 1999 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 microfilm, without permission in writing f
14、rom the ITU. 11 G series - Supplement 38 (10/98) STD*ITU-T RECMN SERIES G SUPP 38-ENGL 3998 48b2593 Ob54889 254 = Supplement 38 to G-series Recommendations VARIABLE BIT RATE CALCULATIONS FOR ITU-T RECOMMENDATION G.767 DIGITAL CIRCUIT MULTIPLICATION EQUIPMENT (DCME) (Geneva, 1998 This Supplement expl
15、ains how the VBR equations were derived. The same notations of Recommendation G.767 are used here. The notation (X, Y, Z) shall be used to note that N16 = X, N12.8 = Y and N9,6 = Z, i.e. X QBs of the bearer carry trafEc at 16 kbits, Y QBs at 12.8 kbit/s and Z QBs at 9.6 kbit/s. In this Combination,
16、X+Y+Z QBs are used to support traffic from up to X + -Y + -Z BCs. If NV is greater than NQB, then VBR is required to create the additional overload channels. Creation of the extra channels can be done using several combinations of NI6, NI, and N9,6. If, for example, there are 19 BCs that need bearer
17、 resources and 15 available QBs, then several combinations exist that use the available resources and support this traffic. Some combinations create more BCs than required, like (2,4,9) that creates 22 BCs or (1, 8, 6) that creates 21 BCs. These combinations support all traffic from all BCs but the
18、average bit rate is not optimal since additional unused BCs are created. Obviously, a combination that creates too few BCs is not acceptable. Other combinations do not use all available QBs but still support all traffic, like (4,4,6) that uses only 14 QBs of the list to create 19 BCs, but, again, su
19、ch combinations lower the bit rate as the bearer resources are not optimally utilized. One exceptional case needs special attention: If NOB is a multiplier of 3 and also N, = - NI - 1 , there is no combination that creates exactly Ny BCs and an additional unused BC must be created. For example, if N
20、QB = 3, it is possible to create 3 channels (each QB carries one voice channel at 16 kbits) or 5 channels (the 3 QBs carry five 9.6 kbits channels), but it is not possible to create exactly 4 channels. To this point, an optimized combination is one that provides the highest bit rate and highest util
21、ization supporting traffic from all BCs in the voice list. This means that no unnecessary additional BCs are created and all the QBs of the list are used. Given NV and NQB there still may be more than one combination that meets these requirements. Advancing the above example, both (9, O, 6) and (4,
22、8, 3) use all 15 QBs, create no unused BCs and provide the same bit rate - 1.58 biusample. So another criterion is required to choose a unique combination. The criterion will be: Prefer creation of as few 9.6 kbit/s channels as possible. In the given example, the second combination is favourable sin
23、ce it uses less 9.6 kbits channels, even though it also uses less 16 kbit/s than the first combination. The motivation to use this criterion is that linear decrease of the bit rate might result in a steeper deterioration of speech quality so, when more 9.6 kbit/s channels are used, even when the ave
24、rage bit rate is maintained, the total quality decreases. To sum, the criteria for choosing one unique combination of N16, NI,.* and N9,6 are: a) b) c) 55 43 5 3 I Maximize instantaneous average bit rate of the traffic while using available bearer resources. Create enough channels for all BCs in the
25、 voice list. Minimize the number of 9.6 kbWs channels. G series - Supplement 38 (10/98) 1 STD.ITU-T RECMN SERIES G SUPP 38-ENGL 1998 48b259L 0654890 T7b The formal representation of these criteria is: 5 5 b) N16 7 N12.8 N9.6 NV 4 min( N9.6) Another obvious requirement is: d) N16 is an integer; N12.8
26、 is an integer multiplier of 4; and N9,6 is an integer multiplier of 3. The first criterion is satisfied when all bearer resources are consumed, so that: a) N12.8 + N9.6 The special case, when an unused BC must be created, is handled in the following manner: If NQB is a multiplier of 3 and also N, =
27、-NIB - 1, then Nv is adjusted by adding 1 to its value. After handling this special case, the second criterion is satisfied when exactly the number of required channels are created, so that: 5 3 5 5 b) N16 7 N12.8 7 N9.6 = NV In order to find the unique combination, the third criterion is handled fi
28、rst: N3,6 is an integral multiple of 3, say N9.6 = 3 x Il where 4 is an integer. Then exactly 5 x Il 9.6 kbits channels are created. The maximum number of additional channels that can be created will be achieved if as many of these additional channels will be at 12.8 kbit/s and the rest at 16 kbit/s
29、. The maximum number of channels at 12.8 kbit/s is 5 x int N, -3 x Il /4 which leaves (NI - 3 x I, 1 - 4 x int( NQB - 3 x I, / 4 channels at 16 kbit/s. It is required that the sum of the 9.6 kbit/s, 12.8 kbit/s and 16 kbits channels will be at least Nv: ( - 1) 5x11+5xint ( -3x1, 1 /4 I(- + -3x1,)-4x
30、int(,-jx1, - 1) 2 x I, is an integer. NQB and Nv are also integers so all three quantities can be moved inside the parentheses and the equation is still valid so we get: int (4 -1 - 4- NoB - NY) 2 0 The minimal Il that satisfies this equation is: 2 G series - Supplement 38 (10198) Since I, is an int
31、eger, the solution is: IT = 120, BC = 54 4 5 where a = O if - Nv - Ne, is an integer (because this way the value inside the parentheses is exactly zero) or a = 1 otherwise. If I, is smaller than zero, then it is set to zero since the number of QBs cannot be negative. 6 2 16 7 3 16 After setting the
32、value of N9.6, the first two criteria are simply variables, and their solution is: N12.8 = 4( NV - NQB - Pv=5 Example #1 Case ofNQB= 10 andNV= 13 4 4 I -Nv -NQg =13-10=0.4 -5 0.4 is not an integer therefore Il = 1.4 N. = 3 x int( I,) = 3 8,9, 10, 11 and 12 4,5,6 and 7 12.8 13, 1,2,3 and 4 8,9 and 10
33、 9.6 P, = (BC+ IT) mod Nv = (120 + 54) mod 13 = 5 And the VBR mapping is as follows: two linear equations with two BCs number NOB= 10, Nv= 13 number Ng6= 3, NI2*= 4, N16= 3 Example #2 Case Of NQB = 15 and Nv= 18 4 4 5 5 I, =-Nv-NQB =-18-15=-0.6 -0.6 is smaller than zero, therefore Il= O G series - S
34、upplement 38 (10/98) 3 - - _ STD-ITU-T RECMN SERIES G SUPP 38-ENGL 1998 m g8b2591 Ob54892 849 m BCs number N9.6 = 3 x int(1,) = O (creation of 9.6 kbits channels is not required) mapped to QBs at rate number kbith NI6 = NQB - N12.8 - Ng.6 = 15-12-0 = 3 Assume IT = 79 and BC = 136. Then: P, =(BC+IT)
35、modN, = (79 + 136) mod 18 = 17 And the VBR mapping is as follows: 17 18 I 1 16 2 16 7,8,9,10 and 11 12,13,14,15 and 16 8,9,10 and 11 12.8 12,13,14 and 15 12.8 1 I 3 I 16 I 2,3,4, 5 and 6 I 4, 5,6 and 7 I 12.8 I 4 G series - Supplement 38 (10/98) I . , . . . . STD-ITU-T RECMN SERIES G SUPP 3B-ENGL II
36、998 4Bb259L Ob54894 bLL cries A leries B leries C leries D ;cries E ;eries F ieries G Series H Series I Series J Series K Series L Series M Series N Series O Series P Series Q Series R Series S Series T Series U Series V Series X Series Y Series Z ITU-T RECOMMENDATIONS SERIES Organization of the wor
37、k of the ITU-T Means of expression: definitions, symbols, classification General telecommunication statistics General tariff principles Overall network operation, telephone service, service operation and human factors Non-telephone telecommunication services Transmission systems and media, digital s
38、ystems and networks Audiovisual and multimedia systems Integrated services digital network Transmission of television, sound programme and other multimedia signals Protection against interference Construction, installation and protection of cables and other elements of outside plant TMN and network
39、maintenance: international transmission systems, telephone circuits telegraphy, facsimile and leased circuits Maintenance: international sound programme and television transmission circuits Specifications of measuring equipment Telephone transmission quality, telephone installations, loca Switching
40、and signalling Telegraph transmission Telegraph services terminal equipment Terminals for telematic services Telegraph switching Data communication over the telephone network Data networks and open system communications Global information infrastructure Programming languages Printed in Switzerland Geneva, 1999
