1、INTERNATIONAL TELECOMMUNICATION UNION ITU=T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU VA20 SERIES V: DATA COMMUNICATION OVER THE TELEPHONE NETWORK Interworking with other networks (I 0/96) Support by an ISDN of data terminal equipment with V-Series type interfaces with provision for statistica
2、l multiplexing ITU-T Recommendation V.120 (Previously CCITT Recommendation) STD-ITU-T RECMN V-L20-ENGL 1796 m i862571 Ob27321 T5L m ITU-T V-SERIES RECOMMENDATIONS DATA COMMUNICATION OVER THE TELEPHONE NETWORK 1 - General 2 - Interfaces and voiceband modems 3 - Wideband modems 4 - Error control 5 -Tr
3、ansmission auaiitv and maintenance For further details, please refer to ITU-T List of Recommendations. STD=ITU-T RECMN V-120-ENGL L99b m 4862593 Ob27322 798 m FOREWORD The ITU-T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (ITU). The IT
4、U-T is responsible for studying technical, operating and tariff 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 fo
5、r study by the IT-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 (Helsinki, March 1-12, 1993). ITLJ-T Recommendation V.120 was revised by ITU-T St
6、udy Group 14 (1993-1996) and was approved by the WTSC (Geneva, 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 appe
7、ndices attached to the Series V Recommendations should be interpreted as - - an annex to a Recommendation forms an integral part of the Recommendation; an appendh to a Recommendation does not form part of the Recommendation and only provides some complementary explanation or information specific to
8、that Recommendation. O IT 1997 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 from the IT. Recommendation V.120 (10196) 1 STD-ITU-T RECMN V-120-E
9、NGL L77b D lr8b257L Ob27323 824 D 1 2 3 4 5 6 7 CONTENTS Scope Application . 2.1 General 2.2 Connectivity 2.3 Protocol architecture . 2.4 Operation over restricted transport capabilities Terminal adaption protocol . : 3.1 Formats . 3.2 Procedures Data link control protocol 4.1 Data link control mode
10、s of service . 4.2 Data link connection verification procedures . Protocol specifications for operation over Frame Mode Bearer service 5.2 Data link protocol . 5.3 Signalling protocol Protocol specifications for operation over Circuit Mode Bearer service . 6.1 Physical protocol 6.2 Data link core pr
11、otocol . 6.3 Signalling protocols Application of teminal adaption protocol to terminal adaptor functions 7.1 Clock synchronization 7.2 Asynchronous mode operation . 7.3 Protocol sensitive synchronous mode operation . 7.4 5.1 Physical protocol Bit transparent mode operation . Annex A . List of variab
12、les . Annex B . Alphabetical list of abbreviations used in this Recommendation . Annex C . Support ofV.42 bis data compression C . 1 Introduction C.2 Negotiationhdication of use of the V.42 bis procedure and its parameter values C.3 C.4 Information fields in XID frames . C.5 Flow control and asynchr
13、onous-break handling . Reference . Appendix I - TE1 application . . 1.1 Asynchronous mode operation . 1.2 Synchronous mode operation . 1.3 Bit transparent mode operation . 1.4 TE1 control state variable processing . Appendix II - Mapping of interface at R reference point circuits to control state in
14、formation Commonly supported interface leads Appendix III - Clock synchronization . Parameters of the data link control entity . 11.1 11.2 Control procedures 11 Recommendation V.120 (10/96) Page 1 1 1 2 3 4 4 5 7 11 11 11 12 12 12 12 12 12 13 14 25 25 25 26 27 27 27 29 29 29 30 30 32 33 34 34 34 35
15、35 36 36 37 38 STDoITU-T RECMN V-120-ENGL L97b 4b259L Ob27324 7b0 m Recommendation V.120 SUPPORT BY AN ISDN OF DATA TERMINAL EQUIPMENT FOR STATISTICAL MULTIPLEXING WITH V-SERIES TYPE INTERFACES WITH PROVISION (Melbourne 1988, modified Geneva I992 and 1996) 1 Scope This Recommendation describes a pro
16、tocol that can be used for adapting terminals with non-ISDN standard network interfaces to an ISDN. It is intended to be used between two Terminal Adaptor (TA) functional groups, between two ISDN terminal (TE1) functional groups, between a TA and a TE1, or between either a TA or TE1 and an interwork
17、ing facility inside a public or private ISDN. It provides for operation: a) over either circuit-mode or fiame-mode connections; b) using either demand or semi-permanent establishment of communications; and c) over any of the following types of access channel: - for circuit-mode connections: B, Ho, H
18、lo or H11; - for fiame-mode connections: B, Ho, Hlo, Hl1 or D. This Recommendation also describes how this protocol is related to synchronous and asynchronous interface specifications using the interchange circuits defined in Recommendation V.24. It is not intended to be a functional specification f
19、or an implementation of any system containing a TE1 or TA functional group. Except as explicitly noted, it is restricted to the definition of the protocol at the user-network interface (reference points S, T or U) and the ISDN-side interface of the Interworking Function (IWF). The terminal adaption
20、protocol in this Recommendation may be used in support of three classes of non-ISDN-terminal protocols. These are: I) Asynchronous (stadstop) protocols, supported using the protocol sensitive asynchronous mode; 2) Synchronous protocols using High-level Data Link Control procedure (HDLC) fiame format
21、, supported using the protocol sensitive synchronous mode; 3) Synchronous protocols, supported using the bit transparent mode. The use of the bit transparent mode with frame mode connections is for further study. 2 Application 2.1 General The protocols described in this Recommendation may be used by
22、 a TE1, TA or IWF, as illustrated in Figure 1. The formats and procedures contained in this Recommendation are defined in terms of their operation across interfaces at reference points S, T or U, or (in the case of an IWF) across interfaces that may be internal network interfaces. Where necessary to
23、 promote compatibility, the relationship between the terminal adaption protocd and existing protocols at the interface at reference point R (where present) are also described. Recommendation V.120 (10/96) 1 STD-ITU-T RECMN V-LZO-ENGL L79b = 48b257L Ob27325 bT7 - TE1 Sff SIT TE1 - 2.2 Connectivity Tw
24、o or more terminai adaption connections may be multiplexed across a circuit-mode bearer connection or frame-mode access connection. These connections are referred to in this Recommendation as “logical links“. Logical links supporting different modes of the terminal adaption protocol may be multiplex
25、ed across the same circuit switched bearer connection or fiame-mode access connection. Constraints on the number of logical links (up to the maximum number that can be coded in the Address field) and the combinations of modes supported by a circuit switched bearer connection or frame- mode access co
26、nnection are implementation dependent and are beyond the scope of this Recommendation. The protocol sensitive modes (1 and 2 above in clause 1) of this Recommendation may be used to support dissimilar rates (i.e. when used between two TAS, the data rates at the interfaces at reference point R may be
27、 different). The use of buffering, application of the flow control protocol in this Recommendation, use of flow control procedures at the R reference point, use of discarding and other strategies for support of dissimilar rates are implementation dependent. Parameter exchange procedures may be defin
28、ed to allow interworking between Terminal Adaptors (TAS) in an environment where multiple different TA protocols are used without requiring interworking functions within the network. Interworking between different types of TAS can be accomplished with Multiprotocol Terminai Adaptors (MTAs) that are
29、capable of supporting more than one protocol. However, interworking functions may be used when TAS are not capable of supporting more than one protocol. TE1 ISDN data terminal equipment TE2 TA-V IWF Interworking function STT PSTN Public Switched Telephone Network Terminal equipment (DTE with non-ISD
30、N interfaces) V.120 terminal adapter supporting V-Series TE2s S or T architecturai reference points at which physical interfaces of concern may be implemented. FIGURE 1N.120 ISDN connection scenarios 2 Recommendation V.120 (10196) STDDITU-T RECMN V=LZU-ENGL L79b 9Bb259L Ob2732b 533 = Header 2.3 Prot
31、ocol architecture Terminal adaptation data field Figure 2 shows the protocol architecture of the U-plane, defined for the purposes of this Recommendation. The protocol defined in this Recommendation may be viewed as having the physical layer and three sublayers: the core sublayer, the data link cont
32、rol sublayer and the adaption sublayer. The core sublayer and the data li control sublayer are subdivisions of the data link layer (see Recommendation X.212). The adaption sublayer may also be considered a subdivision of the data link layer (though it may alternatively be viewed as a thin layer 3) T
33、his layering is in alignment with Recommendation 1.233, “ISDN fiame mode bearer services”. C I Terminal adaptation sublayer Data link control information field Data link control field Data link control sublayer Data link core sublayer FA Data link core information field FCS I Physical layer F Data l
34、ink core frame FIGURE 2N.120 Protocol layers used in this Recommendation Figure 3 shows how the layering of Figure 2 maps to the fiame formats of this Recommendation. I / I / 1 Terminal adaptation field F HDLCflag A Address FCS Frame Check sequence C Control (HDLC format) H CS Header octet (optional
35、 for bit transparent mode) Optional header extension for control state information T1403170-97/403 FIGURE 3N.120 Relationship between layering and frame formats 2.3.1 Terminal adaption sublayer The terminal adaption sublayer provides for transfer of data, provision for the detection of errors, and r
36、eassembly of segmented data between peer systems. It may also provide the following functions: 1) segmentation; 2) transport of notification of error conditions detected in external protocols (ie. at the interface at reference point R); Recommendation V.120 (10/96) 3 STD-ITU-T RECMN V-120-ENGL L77b
37、48b257L b27327 q7T m 3) transport of information related to the normal operation of external products (e.g. break for the protocol sensitive asynchronous mode, HDLC idle for the protocol sensitive synchronous mode); support for operation with a network independent clock; 4) 5) flow control; 6) trans
38、port of status information (which may be mapped to interchange circuits at the interface at reference point R; however, see Appendix II). 2.3.2 Data link control sublayer The data link control sublayer provides the procedures and formats of fields for data link layer peer-to-peer communication. The
39、elements of procedures defne the commands and responses that are used for peer-to-peer communication. For formats and the elements of procedures, see Recommendation 4.922. 2.3.3 Data link core sublayer The data link core sublayer allows for the statistical multiplexing of core information flows. The
40、 major core functions include: - framing; - transparency; - - error detection. multiplexing using the address field; and The data link core protocol is defined in Annex AiQ.922. The data link core service is defined in Recommen- dation 1.233.1. The HDLC frame at the S or T interface is referred to h
41、ereafter as the terminal adaption kame (it includes the HDLC address and control fields, the terminal adaption header and user data). 2.4 Operation over restricted transport capabilities Where a terminal adapter is used on an ISDN user interface for adaptation to a 64 kbit/s B-channel and the bearer
42、 capability provided by the ISDN is “restricted” 64 kbit/s, or the connection involves interworking with a 56 kbits network, the TA shall rate adapt to 56 kbit/s rate by using the first 7 bits of each B-channel octet and shall insert a binary ONE in the eighth bit of each B-channel octet as describe
43、d in Recommendation 1.464. The reverse process shall be used at a receiver. All of the procedures in this Recommendation are applicable to these transport capabilities as well as 64 kbit/s unrestricted transport capabilities. NOTE - In frame mode applications, the limitation, if it exists, will be i
44、n the access capability only. 3 Terminal adaption protocol This clause describes the terminal adaption protocol. This protocol depends upon the services of the data li control sublayer and, for the bit transparent mode, it also depends upon the services of the physical layer (clock). There are two c
45、ategories of terminal adaption defined in this Recommendation. Protocol sensitive operation requires that the TE1, TA or IWF be able to identifj the beginning and end of characters or HDLC fiames, removing any idle time fill. Bit transparent operation provides for the transport of isochronous data t
46、ransparently without alignment (above the bit level) of information from the interface at the R reference point within the frame transport in the bearer channel. It is particularly suited to the adaption of protocols that are not covered by the protocol sensitive modes. Two protocol sensitive modes
47、are defined for the terminal adaption protocol. The asynchronous mode is intended to transport stadstop mode data. The synchronous mode is for the transport of HDLC framed data. 4 Recommendation V.120 (10/96) STD-ITU-T RECMN V-120-ENGL B99b II LiBb259L Ob27328 30b 3.1 Formats The terminal adaption h
48、eader may contain one or two octets. The two are labelled the header (H) octet and the control state (CS) octet. 3.1.1 H-header octet The H octet is mandatory for the protocol sensitive modes of operation, and is optional for the bit transparent mode. The format of the H octet is shown in Figure 4.
49、Its presence in the bit transparent mode is negotiated during call setup for demand connections or by prior agreement for semi-permanent connections. 8 7 6 5 4 3 2 1 Bit I E IBR I res1 res1 c2 I CI I B I F I E Extension bit BR Breaidmark hold bit CI, C2 Error control bits B, F Segmentation bits res Reserved for future standardization FIGURE 4N.120 Header octet format 3.1.1.1 E-extension bi (bit 8) The E-bit is the header extension bit. It allows the extension of the header to provide additional control state information. A “O” bit indicates that a control state (CS
