1、INTERNATIONAL TELECOMMUNICATION UNION ITU=T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU V.300 SERIES V: DATA COMMUNICATION OVER THE TELEPHONE NETWORK Modems on digital circuits (07/99) A 128 (144) kbit/s data circuit-terminating equipment standardized for use on digital point-to-point leased cir
2、cuits ITU-T Recommendation V.300 (Previously CCITT Recommendation) ITU-T V-SERIES RECOMMENDATIONS DATA COMMUNICATION OVER THE TELEPHONE NETWORK II General Interfaces and voiceband modems Wideband modems Error control Transmission quality and maintenance Simultaneous transmission of data and other si
3、gnals Interworking with other networks Interface layer specifications for data communication v.1-v.9 V.10-V.34 v.35-v.39 v.40-v.49 v.50-v.59 V.60-V.99 v. 100-v.199 V.200-V.249 V.250-V.299 II Control procedures Modems on digital circuits V.300-V.399 n For further details, please refer to ITU-T List o
4、f Recommendations. ITU-T RECOMMENDATION V.300 A 128 (144) kbit/s DATA CIRCUIT-TERMINATING EQUIPMENT STANDARDIZED FOR USE ON DIGITAL POINT-TO-POINT LEASED CIRCUITS Summary This Recommendation specifies the necessary functions of a 64, 128 and 144 kbit/s DCE for the is covered. The recommended functio
5、ns also allow this DCE to be deployed as a remote access to a flexible multiplexer as specified in Recommendation G.797. The V.24 and X.24 DTE-DCE interfaces are specified in terms of functions and electrical characteristics. The use of additional interfaces is not precluded. Core functions include
6、scrambling of data, testing facilities, optional aggregation function and optional multiplexing function. This type of DCE may be part of a managed network. This Recommendation contains three appendices providing information on complementary functions or applications for this type of equipment. , pr
7、ovision of digital leased circuits. Intenvorking with DCEs complying with Recommendation V.3 8 Source ITU-T Recommendation V.300 was prepared by ITU-T Study Group 15 (1997-2000) and was approved under the WTSC Resolution No. 1 procedure on the 2nd of July 1999. Recommendation V.300 (07/99) 1 FOREWOR
8、D 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 responsible for studying technical, operating and tariff questions and iss
9、uing 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 the ITU-T Study Groups which, in their turn, produce Recommendations on
10、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 standards are prepared on a collaborative basis with IS0 and IEC. NOTE In
11、this Recommendation the term recognized operating agency (ROA) includes any individual, company, corporation or governmental organization that operates a public correspondence service. The terms Administration, ROA and public correspondence are defined in the Constitution of the ITU (Geneva, 1992).
12、INTELLECTUAL PROPERTY RIGHTS The ITU draws attention to the possibility 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 Proper
13、ty Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, the ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However,
14、implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. O ITU 1999 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, includin
15、g photocopying and microfilm, without permission in writing from the ITU. Il Recommendation V.300 (07/99) . 1 2 3 4 4.1 4.2 5 5.1 5.2 6 6.1 6.2 7 8 8.1 8.2 9 10 STD ITU-T RECMN V-300-ENGL 1999 48b2591 0bb4284 185 CONTENTS Page Scope References Abbreviations . Signalling rates . Data signalling rates
16、 . Signalling rates on line . Differentiation between user and network data signals Scrambler Descrambler Interfaces V.24-type interface 3 . 6.1.1 List of interchange circuits 6.1.2 Electrical characteristics 6,1.3 Operational requirements List of interchange circuits 6.2.3 Operational requirements
17、X.24-type interface 7 . 6.2.1 6.2.2 Electrical characteristics Start-up procedure Testing facilities . Test loops . 8.1.1 Instigation of remote loop 2/2b . 8.1.2 Self tests . 8.2.1 Self test with the type-3 loop 8.2.2 Self test with remote loop 2/2b . Multiplexing . Internal management Instigation o
18、f the type-3 loop Appendix I . Functional block diagram Appendix II . Connection schematics . Appendix III . Example of implementation of the transmission unit . 111.1 General . 111.2 Physical model of the line transmission system . Recommendation V.300 (07/99) 1 2 3 3 3 3 3 4 4 4 4 5 6 6 6 7 7 7 9
19、9 10 11 12 12 12 iii STD-ITU-T RECMN V-300-ENGL L999 4862573 0664285 O31 111.3 111.4 Functional description of the DCE . Functions of TU functional block 111.4.1 Data channels 111.4.2 DCE management channel 111.4.3 Bit timing 111.4.4 Octet timing . 111.4.5 Frame alignment 111.4.6 Activation 111.4.7
20、Deactivation 111.4.8 Power feeding 111.4.9 Maintenance 111.5 Requirements for a line transmission system using 2B 1 Q line code . 111.5.1 Line code . 111.5.2 Line modulation rate . 111.5.3 Clock tolerance 111.5.4 Frame structure 111.5.5 Frame and multiframe words 111.5.6 Frame offset between slave T
21、U and master TU 111.5.7 CL channel 111.6 DCE management channel . 111.6.1 Protocol and procedure . 111.6.2 Functions provided 111.7 Equipment management function . 111.7.1 General 111.7.2 Specific functions of the equipment management function with TU working in slave mode 111.7.3 Specific functions
22、 of equipment management function with TU working in master mode Page 13 13 14 14 14 15 15 15 15 15 15 15 15 16 16 16 16 17 17 19 19 19 19 19 20 20 iv Recommendation V.300 (07/99) STD-ITU-T RECMN V-300-ENGL 1999 4b2591 Ohh42h T5 m Recommendation V.300 A 128 (144) kbit/s DATA CIRCUIT-TERMINATING EQUI
23、PMENT STANDARDIZED (Geneva, 1999) FOR USE ON DIGITAL POINT-TO-POINT LEASED CIRCUITS 1 Scope This data circuit-terminating equipment (DCE) is intended for use on n x 64 kbit/s based digital point-to-point leased circuits other than ISDN. Signalling rates supported by the equipment are 64 kbits and 12
24、8 kbit/s. This may be expanded to 144 kbits when a digital leased line network supports this type of connection, or for DCE interconnection on short haul leased circuits employing metallic pair(s). The DCE is specified herein in terms of the DTE-to-DCE interface(s) and features including rate adapta
25、tion, end-to-end signalling, testing and multiplexing facilities. The line signal and the line signalling rate that are used to connect this type of DCE locally to a number of 64 kbit/s. or 128 kbits or 144 kbit/s, digital bearer circuit(s) are considered to be national matters, and are hence not sp
26、ecified herein. The transmission scheme chosen should, however, be capable of providing an octet timing recovery where a multiplexing function as specified in clause 9 is employed. The principal characteristics of the DCE are as follows: a) b) cl d) inclusion of testing facilities; 4 0 g h) i) NOTE
27、1 - Figure i.1 gives a schematic block diagram of the arrangement of functional blocks (without the multiplexer function) inside the DCE. NOTE 2 -The term “line signalling rate“ as used in the context of this Recommendation refers to the signalling rate at the input of the transmitter of the transmi
28、ssion unit (see Figure 1.1). NOTE 3 - The use of additional DTE-DCE interfaces, e.g. codirectional G.703 64 kbit/s SI, 1.430 i 13 or G.703G.704 9/ 1 O is not precluded. duplex mode of operation on digital leased circuits; signalling rates of 64 and 128/144 kbits; inclusion of two (Note 3) different
29、types of DTE-DCE functional interfaces; optional provision of a means to differentiate between user and network data; optional inclusion of a multiplexer (for further study); optional inclusion of an equipment management function; inclusion of an optional aggregation function; backward compatibility
30、 with a DCE according to Recommendation V.38 4. Recommendation V.300 (07/99) 1 STD-ITU-T RECMN V-300-ENGL L999 48b259L 0664287 994 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in the text, constitute provisions of this Recommendati
31、on. 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 therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other reference
32、s listed below. A list of the currently valid ITU-T Recommendations is regularly published. ITU-T Recommendation V. 1 O (1 993), Electrical characteristics for unbalanced double-current interchange circuits operating at data signalling rates nominally up to I O0 kbit/s. ITU-T Recommendation V. 1 1 (
33、1 996), Electrical characteristics for balanced double-current interchange circuits operating at data signalling rates up to 10 Mbit/s. ITU-T Recommendation V.24 (1 996), List of definitions for interchange circuits between data terminal equipment (DTE) and data circuit-terminating equipment (DCE).
34、ITU-T Recommendation V.38 (1 996), A 48/56/64 kbit/s data circuit-terminating equipment. standardized for use on digital point-to-point leased circuits. CCITT Recommendation V.54 (1 988), Loop test devices for modems. CCITT Recommendation X.2 1 (1 992), Interface between data terminal equipment and
35、data circuit-terminating equipment for synchronous operation on public networks. CCITT Recommendation X.24 (1988), List of definitions for interchange circuits between data terminal equipment (DTE) and data circuit-terminating equipment (DCE) on public data networks. CCITT Recommendation X.150 (1988
36、), Principles of maintenance testing for public data networks using data terminal equipment (DTE) and data circuit-terminating equipment (DCE) test loops. ITU-T Recommendation G.703, (1998), Physical/eZectrical characteristics of hierarchical digital interfaces. ITU-T Recommendation G.704 (1 998), S
37、ynchronous frame structures used at 1.544, 6322, 2048, 8448 and 44 736 kbith hierarchical levels. ITU-T Recommendation 1.430 (1 995), Basic user-network interface - Layer I speczjkation. CCITT Recommendation O. 153 (1 992), Basic parameters for the measurement of error performance at bit rates below
38、 the primary rate. IS0 4902: 1989, Information technology - Data communication - 3 7-pole DTE/DCE interface connector and contact number assignments. IS0 4903: 1989, Information technology - Data communication - 1.5-pole DTE/DCE interface connector and contact number assignments. ISOIEC 11 569: 1993
39、, Information technology - Telecommunications and information exchange between systems - 26-pole interface connector mateability dimensions and contact number assignments. 2 Recommendation V.300 (0799) - STD-ITU-T RECMN V-300-ENGL Is999 48b259L Obb4288 820 W 3 Abbreviations This Recommendation uses
40、the following abbreviations: AIS Alarm Indication Signal DCE Data Circuit-terminating Equipment DTE Data Terminal Equipment 4 Signalling rates 4.1 Data signalling rates The recommended data signalling rate (user rate, is synclJonous at 128 be supported). 1s (144 kbit/s may also 4.2 Signalling rates
41、on line Data at either signalling rate may be supported by a digital bearer circuit being accessed with a line signalling rate that depends upon the leased line network implementation. This is not in the scope of this Recommendation. Appendix III depicts such an example with a 160 kbit/s line signal
42、ling rate. 5 and network data or network signalling towards the DCE e.g. loss of synchronization or alarm indication signal (AIS), and for fault detection. Where the scrambler/descrambler is provided, its use shall be subject to bilateral agreement between the Administrations concerned. NOTE - The p
43、otential provision of an additional scramblerdescrambler inside the transmission unit of the DCE (see Figure 1.1) is a national matter, and outside the scope of this Recommendation. Differentiation between user and network data signals I An optional scrambler/descrambler may be provided as a means o
44、f differentiating between user data 5.1 Scrambler Where provided, the following self-synchronizing scrambler having the generating polynomial 1 + xWi8 + x-23 shall be used for the transmitter of the DCE. The message data sequence applied to the scrambler shall be effectively divided by the generatin
45、g polynomial. The coeficients of the quotients of this division, taken in descending order, form the data sequence which shall appear at the output of the scrambler. The scrambler data output sequence thus shall be: D, = Di O D, x-* (3 D, e x-23 where: D, is the data sequence at the output of the sc
46、rambler Di is the data sequence applied to the scrambler Do is the data sequence at the output of the descrambler (see 5.2) denotes modulo 2 addition denotes binary multiplication Recommendation V.300 (07199) 3 Figure 1 shows a suitable implementation. - D D . x-23 S I-I T1400270-93 Figure 1N.300 -
47、Scrambler 5.2 Descrambler Where the scrambler specified in 5.1 is provided, also a self-synchronizing descrambler having the polynomial 1 + x-18 + x-23 shall be provided in the receiver of the DCE. The message data sequence output by the receiver of the transmission unit (see Figure I. 1) shall be e
48、ffectively multiplied by the. generating polynomial 1 + x-18 + x-23 to form the descrambled message. The coefficients of the recovered message sequence taken in descending order form the output data sequence Do, which is given by: Do = D, (I 0 x-“ 0 where the notation is defined in 5.1. Figure 2 sho
49、ws a suitable implementation. I D, . D . .-23 5 T1400280-93 Figure 2N.300 - Descrambler 6 Interfaces One or both types of functional interfaces shall be provided in the DCE, as specified below. It shall be possible that two DCEs in accordance with this Recommendation can interoperate, where in these DCEs the opposite types of interfaces are employed. 6.1 V.24-type interface 3 6.1.1 List of interchange circuits The interchange circuits shall be as in Table 1. 4 Recommendation V.300 (07/99) STD.ITU-T RECMN V-300-ENGL 1999 W 48
