1、INTERNATIONAL TELECOMMUNICATION UN ION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU V.38 SERIES V: DATA COMMUNICATION OVERTHE TELEPHONE NETWORK Wideband modems (I 0196) A 48/56/64 kbit/s data circuit-terminating equipment standardized for use on digital point- to-point leased circuits ITU-T
2、 Recommendation V.38 (Previously CCITT Recommendation) ITU-T V-SERIES RECOMMENDATIONS DATA COMMUNICATION OVER THE TELEPHONE NETWORK 1 1 - General II 2 - Interfaces and voiceband modems 4 - Errorcontrol 5 - Transmission quality and maintenance 6 - Interworking with other networks For further details,
3、 please refer to ITU-TList of Recommendations. STD-ITU-T RECMN V-38-ENGL L77b 48b257L 0b27238 379 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 tari
4、ff questions and issuing 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 IT-T Study Groups which, in their turn, produc
5、e 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 (Helsinki, March 1-12, 1993). ITU-T Recommendation V.38, was prepared by IT-T Shdy Group 14 (1993-1996) and was approved by the WTSC (Geneva,
6、October 9-18, 1996). NOTE 1. telecommunication administration and a recognized operating agency. In this Recommendation, the expression “Administration” is used for conciseness to indicate both a 2. follows: The status of annexes and appendices attached to the Series V Recommendations should be inte
7、rpreted as - - an annex to a Recommendation forms an integral part of the Recommendation; an appendix to a Recommendation does not form part of the Recommendation and only provides some complementary explanation or information specific to that Recommendation. O IT 1997 All rights reserved. No part o
8、f 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 fom the ITU. Recommendation V.38 (10196) 1 1 2 3 4 5 6 7 8 STD-ITU-T RECMN V-3-ENGL L77b 4b257L b27239 200 m CONTENTS Introduct
9、ion Signalling rates . 2.1 Data signalling rates . 2.2 Signalling rates on line . 3.1 Scrambler (64 kbits only) 3.2 Descrambler (64 kbit/s only) Interfaces 4.2 X.24-type interface . Differentiation between user and network data signals 4.1 V.24-type interface . Rate adaptation . Testing facilities .
10、 6.1 Test loops 6.2 Self tests Multiplexing . Internal management Appendix I . Functional block diagram Appendix III -Rate adaptation of data signalling rates below 48 kbits . 111.2 Rate adaptation . Appendix II . Connection schematic 111.1 Data signalling rates . 111.3 Interfaces Appendix IV - Exam
11、ple of implementation of the transmission unit . IV.l General IV.2 Physical model of the line transmission system IV.3 Functional description of the DCE . IV.4 Functions of TU functional block . IV.5 Requirements for a line transmission system using 2B1Q line code IV.6 DCE management channel IV.7 Eq
12、uipment management function . Page 1 1 1 1 2 2 2 3 3 4 5 6 6 6 7 7 7 9 9 9 9 10 10 10 10 11 11 13 15 16 11 Recommendation V.38 (lOj96) STD-ITU-T RECMN V-38-ENGL L77b M 48625911 Ob2724O T22 Recommendation V.38 A 48/56/64 kbit/s DATA CIRCUIT-TERMINATING EQUIPMENT STANDARDIZED FOR USE ON DIGITAL POINT-
13、TO-POINT LEASED CIRCUITS (revised in 1996) 1 Introduction This DCE is intended for use on 56-kbit/s and 64-kbMs digital point-to-point leased circuits other than ISDN. The DCE is specified herein in terms of the DTE-to-DCE interface(s) and features including rate adaptation, end-to-end signalling, t
14、esting and multiplexing facilities. The line signal and the signalling rate that is used to connect this type of DCE locally to a 64-kbit/s digital bearer circuit is considered to be a national matter, and is hence not specified herein. The transmission scheme chosen should, however, be capable of p
15、roviding an octet timing recovery where a rate adaptation as specified in clause 5 is employed. An octet timing may also become necessary where a rate adaptation of data signalling rates below 48 kbitk is accomplished (see Appendix III). The principal characteristics of the DCE are as follows: a) b)
16、 c) d) rate adaptation of 48 kbits and 56 kbit/s into 64 kbiiis according to schemes specified in duplex mode of operation on digital leased circuits (see Note i); gross bit rates of at least 56 kbits; signalling rates up to 56/64 kbit/s; Recommendation V.110; inclusion of two different types of DTE
17、-DCE functional interfaces; e) f, inclusion of testing facilities; g) h) i) NOTE 1 - The implementation of an optional half-duplex mode of operation is for further study. NOTE 2 - Figure 1.1 gives a schematic block diagram of the arrangement of functional blocks (without the multiplexer NOTE 3 - The
18、 term “line signalling rate” as used in the context of this Recommendation refers to the signalling rate at the 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 functio
19、n. function) inside the DCE. input of the transmitter of the transmission unit (see Figure 1.1). 2 Signalling rates 2.1 Data signalling rates The recommended data signalling rates (user rates) are synchronous at 48 kbit/s, 56 kbit/s and 64 kbit/s. For certain national applications or upon bilateral
20、agreement between Administrations, also other data signalling rates below 48 kbit/s are applicable (see Appendix III). 2.2 Signalling rates on line Where the data signalling rate is 48 kbiiis or 56 kbit/s, a rate adaptation to 64 kbit/s as specified in clause 5 shall be performed at the connection t
21、o an international 64-kbits bearer circuit. The precise location where this adaptation takes place is a national matter. NOTE - It should be noted that in some networks the provision of an octet timing may become necessary at the transition from transmission at 56 kbit/s to transmission at 64 kbitk.
22、 Details are outside the scope of this Recommendation, and may be associated with the line signal transmission equipment used. However, a schematic possible scenario is depicted in Figure 11.1. Recommendation V.38 (10196) 1 STD-ITU-T RECMN V-38-ENGL 197b m L1b257L b27241 7b7 m 3 Differentiation betw
23、een user and network data signals in some cases it may be desirable to provide a means of differentiating between user and network data (e.g. fault detection). The following optional scrambler is provided as a means of accomplishing this differentiation. NOTE -The potential provision of a scrambler/
24、descrambler inside the transmission unit of the DCE (see Figure I. i) is a national matter, and outside the scope of this Recommendation. 3.1 Scrambler (64 kbit/s only) Optionally and on bilateral agreement of the Administrations concerned, a self-synchronizing scrambler having the generating polyno
25、mial 1 + r18 + r23 may be included in the transmitter of the DCE. The message data sequence applied to the scrambler shall be effectively divided by the generating polynomial. The coefficients of the quotients of this division, taken in descending order, form the data sequence which shall appear at
26、the output of the scrambler. The scrambler data output sequence thus shall be: D, = Di D, x18 D, xi23 where: D, is the data sequence at the output of the scrambler Di is the data sequence applied to the scrambler Do is the data sequence at the output of the descrambler (see 3.2) 63 denotes modulo 2
27、addition denotes binary multiplication Figure 1 shows a suitable implementation. O, . x-23 T1400270-93/dOl FIGURE 1N.38 Scrambler 3.2 Descrambler (64 kbih only) c. Where the optional scrambler specified in 3.1 is provided, also a self synchronizing descrambler having the polynomial 1 + xd8 + x-23 sh
28、all be provided in the receiver of the DCE. The message data sequence output by the receiver of the transmission unit (see Figure 1.1) shall be effectively multiplied by the generating polynomial 1 + YI8 + x-23 to form the descrambled message. The coefficients of the recovered message sequence taken
29、 in descending order form the output data sequence Do, which is given by: . where the notation is defined in 3.1. Figure 2 shows a suitable implementation. 2 Recommendation V.38 (10196) STD-ITU-T RECMN V.38-ENGL 199b 48b2591 0b272Li2 BT5 I D, . x-* D, x-23 1 T140028 - upon the reception of 256 conse
30、cutive bits in the binary ONE condition where the optional scramblerldescrambler function specified in clause 3 is provided. The DTE should be prepared to receive garbled signals or contiguous binary 1 on circuit R with i = ON, prior to this DCE not ready signal. The critena for the control of the i
31、nterface depending on a received line signal are a national matter, and are outside the scope of this Recommendation. 5 Rate adaptation The bit rate adaptation for 48 kbit/s shall be as specified in Table 7aN.110. For national connections, rate adaptation of 48 kbitls in accordance with Recommendati
32、on X.50 bis may continue to be used as an alternative. The rate adaptation of 56 kbit/s shall be as specified in Table 7bN.110. For national connections, rate adaptation in accordance with Table 7c/ V.110 may be used as an alternative. The precise location where the rate adaptation in accordance wit
33、h the schemes specified above takes place is a national matter. in some national networks, transmission to the international gateway may be at 56 kbids or other line signalling rates or may apply a diferent adaptation scheme, and rate adaptation in accordance with the schemes specified above mayfirs
34、t be accomplished at the intemational gateway. Where the line signalling rate is 56 kbit/s, no adaptation of a data Signalling rate of 48 kbit/s is provided. Recommendation V.38 (10/96) 5 STD-ITU-T RECMN V-38-ENGL L97b 48b2571 Ob27245 504 6 Testing facilities While it is recognized that the primary
35、means of fault detectiodisolation on digital facilities will be accomplished by the network providers through in-service monitoring, the following testing facilities are specified for the case where user initiated fault isolation is desired. The use of the procedure specified in Recommendation V.54
36、is provided, other methods for providing fault isolation are for further study. 6.1 Test loops As in Recommendation V.54, the DCEs are referred to hereafter as DCE A and DCE B. Test loops 2 for the V.24-type interface case, and 2b for the X.24-type interface case, shall be provided. Test loop 3 shal
37、l be provided for the V.24-type interface, and one of the test loops 3a or 3b for the X.24-type interface. The precise location of these type-3 loops is beyond the scope of this Recommendation. The definitions of these test loops are as described in Recommendations V.54 and X.150, respectively. Oper
38、ation and signalling at the DTE-DCE interfaces of DCE A and DCE B shall be as specified in Recommendations V.54 and X.21, respectively. 6.1.1 Instigation of remote loop 2/2b The control of loop 2 (loop 2b respectively) shall utilize the preparation and termination phases as specified in Recommendati
39、on V.54. NOTE - Clauses 5, 6 and 7 of Recommendation V.54 describe the automatic control with synchronous DCEs for simple multipoint circuits, point-to-point duplex circuits and tandem circuits. Only the point-to-point duplex circuit case is applicable where in the DCE the X.24-type interface is emp
40、loyed. Application of the two other configurations with the X.24-type interface is for further study. The instruction of a DCE (DCE A) to instigate a remote loop 2/2b may be manual or automatic. The automatic case shall be upon the recognition of an OFF-to-ON transition on circuit 140 (in the case o
41、f the V.24-type interface) or upon the recognition of a Send loop 2 command (state L21, c = OFF, t = 001 1) (in the case of the X.24-type interface). This means, irrespective of the type of interface employed, scrambling of a binary O with the polynomial 1 + fi + r7 and transmitting it as though it
42、was introduced to the DCE via circuit 103 or circuit T, respectively. 6.1.2 Instigation of the type-3 loop The instruction of a DCE to instigate a type-3 loop may be manual or automatic. The automatic case shall be upon the recognition of an OFF-to-ON transition on circuit 141 (in the case of the V.
43、24-type interface) or upon the recognition of a Send loop 3 command (state L3 1, c = OFF, t = O0001 11 1) (in the case of the X.24-type interface). 6.2 Self tests The provision of the self-test function specified herein is optional. The tests described hereafter (in 6.2.1 and 6.2.2) employ an intern
44、ally generated data pattern that is typically controlled by a switch on the DCE. It shall be possible to perfom these tests with or without the DCE being connected to a DTE. Upon activation of the self-test function, an internally generated data pattern at the selected user signalling rate shall be
45、transmitted as though it was introduced to the DCE via circuit 103 or circuit T, respectively (see Figure 1.1). An error detector, capable of identifjkg errors in the test pattern, shall be connected to the received data path. How the presence of errors is indicated is beyond the scope of this Recom
46、mendation. NOTE-The test pattern has no end-to-end bearing. Its specification is therefore not part of this Recommendation. Examples for test patterns may be alternative binary ONES and ZEROS (reversals) or the 51 1-bit test pattern in accordance with Recommendation 0.1 53. During any self-test mode
47、, interchange circuits 103, 105 and 108/2 (where provided) at the V.24-type interface, and interchange circuits T imd C at the X.24-type interface, shall be ignored. 6 Recommendation V.38 (10/96) At the V.24-type interface, all generating interchange circuits except 114 (if used), 1 15 and 142 shall
48、 be clamped to the binary 1 or OFF condition. If circuit 113 is used, the DCE shall disregard this interchange circuit and shall use its internal clock. At the X.24-type interface, the DCE shall signal state DCE not ready (r = O, i = OFF) to the DTE. If circuit X is used, the DCE shall disregard thi
49、s interchange circuit and shall use its internal clock. 6.2.1 The type-3 loop as defined in Recommendations V.54 and X.150, respectively, shall be activated in the DCE. The self- test function shall be activated, and the DCE operation shall be as described in 6.2. Self test with the type-3 loop 6.2.2 The DCE shall be conditioned to instigate a 2/2b at the remote DCE as specified in 6.1.1. The self-test function shall be activated, and the DCE operation shall be as described in 6.2. Self test with remote loop 2/2b 7 Multiplexing A multiplexing option may be in
