1、STD-ITU-T RECMN Xmb25-ENGL L77b qBb259L Ob250b5 75b W I NTERNATI ONAL TELECOMMUNICATION UN ION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU X.625 (I 0/96) SERIES X: DATA NETWORKS AND OPEN SYSTEM COM M U N I CATI ON OS1 networking and system aspects - Networking Information technology - Prot
2、ocol for providing the connectionless-mode network service: Provision of the underlying service by ISDN circuit-switched B-channels ITU-T Recommendation X.625 (Previously “CCITT Recommendation”) STD-ITU-T RECMN X.bZ5-ENGL L77b 48b2571 ObZ50bb b72 W ITU-T X-SERIES RECOMMENDATIONS DATA NETWORKS AND OP
3、EN SYSTEM COMMUNICATION PUBLIC DATA NETWORKS Services and facilities Interfaces Transmission, signalling and switching Network aspects Maintenance Administrative arrangements Model and notation Service definitions Connection-mode protocol specifications Connectionless-mode protocol specification PIC
4、S proformas Protocol Identification Security Protocols Layer Managed Objects Conformance testing General Satellite data transmission networks MESSAGE HANDLING SYSTEMS OPEN SYSTEM INTERCONNECTION INTERWORKING BETWEEN NETWORKS X.1-X.199 X. l-X. 19 X.20-X.49 X.50-X.89 X.90-X. 149 X.150-X.179 X. 180-X.
5、199 X.200-X.299 X.200-X.209 X.2 10-X.2 19 X.220-X.229 X.230-X.239 X.240-X.259 X.260-X.269 X.270-X.279 X.280-X.289 X.290-X.299 X.300-X.399 X.300-X.349 X.350-X.399 X.400-X.499 DIRECTORY X. 5 00-X. 599 Efficiency Naming, Addressing and Registration Abstract Syntax Notation One (ASN. 1) Systems Manageme
6、nt framework and architecture Management Communication Service and Protocol Structure of Management Information Management furictions OS1 MANAGEMENT SECURITY OS1 APPLICATIONS Commitment, Concurrency and Recovery Transaction processing Remote operations OPEN DISTRIBUTED PROCESSING X.630-X.649 X.650-X
7、.679 X.680-X.699 X.700-X.799 X.700-X.709 X.7 10-X.7 19 X.720-X.729 X.730-X.799 X.800-X.849 X.850-X.899 X.850-X.859 X.860-X.879 X.880-X.899 X.900-X.999 For further details, please refer to ITU-T List of Recommendations. FOREWORD ITU (Intemational Telecommunication Union) is the United Nations Special
8、ized Agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the ITU. Some 179 member countries, 84 telecom operating entities, 145 scientific and industrial organizations and 3 8 international organizations participate in ITU-T whi
9、ch is the body which sets world telecommunications standards (Recommendations). The approval of Recommendations by the Members of ITU-T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsinki, 1993). In addition, the World Telecommunication Standardization Conference (WTSC), which m
10、eets every four years, approves Recommendations submitted to it and establishes the study programme for the following period. 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. The text of ITU-T Re
11、commendation X.625 was approved on 5th of October 1996. The identical text is also published as ISOAEC International Standard 8473-5. NOTE In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating ag
12、ency. O ITU 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 ITU, except as noted in footnote 1) in Annex A. ITU-T Rec. X.625 (1996 E
13、) 1 STD-ITU-T RECMN XOb25-ENGL L97b m 48b25L Ob250b8 4b5 m CONTENTS Scope Normative references . 2.1 Identical Recommendations I International Standards 2.2 Paired Recommendations I International Standards identical in technical content . 2.3 Additional references Definitions 3.1 Reference model def
14、initions . 3.2 3.3 Network layer addressing definitions . Abbreviations . Subnetwork dependent convergence function 5.1 General model . 5.2 Subnetwork user data 5.3 Subnetwork dependent convergence functions used with ISDN circuit-switched B-channel Conformance 6.1 Static conformance Network layer a
15、rchitecture definitions 6.2 Dynamic conformance 6.3 PICS proforma Annex A . PICS proforma A.l introduction . A.2 Abbreviations and special symbols . A.3 Instructions for completing the PICS proforma A.4 Identification . AS Subnetwork dependent convergence functions for use with X.25 subnetworks . Pa
16、ge 1 1 1 1 1 2 2 2 2 2 3 3 3 4 7 7 7 7 8 8 8 8 10 11 11 ITU-T Rec . X.625 (1996 E) Summary This Recommendation I International Standard specifies the way in which the underlying service assumed by the protocol defined by IT-T Rec. X.223 I ISOfiEC 8473-1 is provided by a subnetwork that conforms to R
17、ecommen- dation 4.93 1 through the operation of a Subnetwork Dependent Convergence Function (SNDCF). This Recommendation I International Standard also provides the PICS proforma for this protocol, in compliance with the relevant requirements, and in accordance with the relevant guidance given in Rec
18、ommendation X290. Introduction This Recommendation I International Standard is one of a set of Recommendations and International Standards produced to facilitate the interconnection of open systems. The set covers the services and protocols required to achieve such interconnection. This Recommendati
19、on 1 International Standard is positioned with respect to other related Recommendations and International Standards by the layers defined in IT-T Rec. X.200 I ISOAEC 7498-1. In particular, it defines the way in which the B-channels of an ISDN subnetwork may be used within the Network layer to provid
20、e the abstract underlying service with respect to which the protocol defined by IT-T Rec. X.233 I ISODEC 8473-1 is specified. in order to evaluate the conformance of a particular implementation of this protocol, it is necessary to have a statement of which of the protocols capabilities and options h
21、ave been implemented. Such a statement is called a Protocol implementation Conformance Statement (PICS), as defined in CCITT Rec. X.290 and ISOfiEC 9646-1. A PICS proforma, from which a PICS may be prepared for a specific implementation, is included in this Recommendation I International Standard as
22、 Annex A. . ITU-T Rec. X.625 (1996 E) 111 STD-ITU-T RECMN X.bZ5-ENGL 1776 H i862571 Ob25070 013 H STD-ITU-T RECMN X-bZ5-ENGL 177b 48b257L Ob25071 T5T W ISO/IEC 8473-5 : 1997 (E) INTERNATIONAL STANDARD ITU-T RECOMMENDATION INFORMATION TECHNOLOGY - PROTOCOL FOR PROVIDING THE CONNECTIONLESS-MODE NETWOR
23、K SERVICE: PROVISION OF THE UNDERLYING SERVICE BY ISDN CIRCUIT-SWITCHED B-CHANNELS 1 Scope This Recommendation I International Standard specifies the way in which the underlying service assumed by the protocol defined by ITU-T Rec. X.233 I ISOAEC 8473-1 is provided by a subnetwork that conforms to R
24、ecommen- dation 4.931 through the operation of a Subnetwork Dependent Convergence Function (SNDCF) as described in ISO/IEC 8648. This Recommendation I International Standard also provides the PICS profonna for this protocol, in compliance with the relevant requirements, and in accordance with the re
25、levant guidance, given in CCITT Rec. X.290 and ISO/IEC 9646- 1. 2 Normative references The following Recommendations and International Standards contain provisions which, through reference in this text, constitute provisions of this Recommendation I International Standard. At the time of publication
26、, the editions indicated were valid. All Recommendations and Standards are subject to revision, and parties to agreements based on this Recommendation I International Standard are encouraged to investigate the possibility of applying the most recent edition of the Recommendations and Standards liste
27、d below. Members of IEC and IS0 maintain registers of currently valid International Standards. The Telecommunication Standardization Bureau of the IT maintains a list of currently valid IT-T Recommendations. 2.1 Identical Recommendations 1 International Standards - ITU-T Recommendation X.200 (1994)
28、1 ISOAEC 7498-1:1994, Information technology - Open Systems Interconnection - Basic Reference Model: The Basic Model. CCITT Recommendation X.213 (1992) I ISOAEC 8348:1993, Information technology - Open Systems Inferconnection -Network service dejnition. IT-T Rec. X.233 (1993) I ISO/IEC 8473-1:1994,
29、Information technology - Protocol for providing the connectionless-mode Network service: Protocol specification. IT-T Rec. X.622 (1994) I ISOAEC 8473-3:1995, Information technology - Protocolfor providing the connectionless-mode Network service: Provision of the underlying service by an X.25 subnetw
30、ork. IT-T Rec. X.623 (1994) I ISOAEC 8473-4:1995, Information technology - Protocol for providing the connectionless-mode Network service: Provision of the underlying service by a subnetwork that provides the OSI data link service. - - - - 2.2 Paired Recommendations 1 International Standards identic
31、al in technical content - CCITT Recommendation X.290 (1992), OSI conformance testing methodology and j-amework for protocol Recommendations for CCITT applications - General concepts. ISOAEC 9646- 1 : 1994, Information technology - Open Systems Interconnection - Conformance testing methodology andpam
32、ework - Part I: General concepts. 2.3 Additional references - - - CCITT Recommendation 1.23 1 (1988), Circuit-mode bearer service categories. IT-T Recommendation 1.430 (1993), Basic user-network interface - Layer 1 specification. IT-T Recommendation 1.431 (1993), Primary rate user-network interface
33、-Layer 1 specijkation. ITU-T Rec. X.625 (1996 E) 1 STD-ITU-T RECMN Xmb25-ENGL L77b = 48b259L Ob25072 77b W ISO/IEC 8473-5 : 1997 (E) ITU-T Recommendation 4.92 1 (1993), ISDN user-network interface - Data link layer specification. ITU-T Recommendation 4.93 1 (1993), Digital Subscriber Signalling Syst
34、em No. I (DSS 1) - ISDN user-network interface layer 3 specification for basic call control. ITU-T Recommendation X.25 (1 993), Interface between Data Terminal Equipment (DTE) and Daia Circuit-terminating Equipment (DCE) for terminals operating in the packet mode and connected to public data network
35、s by dedicated circuii. CCITT Recommendation X. 121 (1992), International numberingplan for public data networks. ISOiEC 7716: 1995, Information technology - Telecommunications and information exchange between systems - High-level data link control procedures - Description of the X.25 LAPB-compatibl
36、e DTE data link procedures. ISOtiEC 8208:1995, Information technology - Data communications - X.25 Packet Layer Protocol for Data Terminal Equipment. IS0 8648: 1988, Information processing systems - Open Systems interconnection - Internal organization of the Network Layer. ISOAEC 1 1575: 1995, Infor
37、mation technology - Telecommunications and information exchange between systems - Protocol mappings for the OS1 Data Link service. 3 Definitions 3.1 Reference model definitions This Recommendation I International Standard makes use of the following terms defined in ITU-T Rec. X.200 1 ISOflEC 7498-1
38、: a) network entity; b) Network layer; c) service; d) service data unit; e) protocol control information. 3.2 Network layer architecture definitions This Recommendation I International Standard makes use of the following terms defined in ISOAEC 8648: a) subnetwork; b) subnetwork dependent convergenc
39、e protocol; c) subnetwork dependent convergence function; d) subnetwork access protocol. 3.3 Network layer addressing definitions This Recommendation I International Standard makes use of the following term defined in CCITT Rec. X.213 I ISOiEC 8348: - subnetwork point of attachment. 4 Abbreviations
40、For the purposes of this Recommendation I International Standard, the following abbreviations apply: CLNP Connectionless-mode Network Protocol DCE Data Circuit-terminating Equipment DTE Data Terminal Equipment ES End System IS Intermediate System 2 ITU-T Rec. X.625 (1996 E) STD*ITU-T RECMN X.bE5-ENG
41、L L99b m 48b257L Ob25073 822 m ISOAEC 8473-5 : 1997 (E) ISDN Integrated Services Digital Network PDU Protocol Data Unit PVC Permanent Virtual Circuit 00s Quality of Service SDU Service Data Unit SN Subnetwork SNDCF Subnetwork Dependent Convergence Function SNDCP Subnetwork Dependent Convergence Prot
42、ocol SNICP Subnetwork Independent Convergence Protocol SNAcP Subnetwork Access Protocol SNPA Subnetwork Point of Attachment SNCR Subnetwork Connection Reference SNSDU Subnetwork Service Data Unit TA Terminal Adapter TE Terminal Equipment 5 Subnetwork dependent convergence function 5.1 General model
43、The general model for providing the underlying service assumed by the protocol in conjunction with a real subnetwork that uses a connectionless subnetwork access protocol is as follows. The generation of an SN-UNIT-DATA Request by the CLNP results in the generation of a corresponding subnetwork-spec
44、ific UNIT-DATA request by the subnetwork dependent convergence function. The receipt of a subnetwork-specific UN IT-DATA indication associated with delivery of a connectionless data unit to its destination causes the SNDCF to generate an SN-UNIT-DATA indication to the CLNP. The general model for pro
45、viding the underlying service assumed by the CLNP in conjunction with a real subnetwork that uses a connection-mode subnetwork access protocol is as follows. The generation of an SN-UNIT-DATA request by the CLNP causes a connection (logical channel, logical link, or the equivalent) to be made availa
46、ble for the transmission of SN-User-data. If a connection cannot be made available, the SN-UNIT-DATA Request is discarded. The receipt of subnetwork-specific PDUs containing SN-User-data causes the SNDCF to generate an SN-UNIT-DATA indication to the CLNP. Where a real subnetwork is designed to use e
47、ither a connectionless-mode or a connection-mode subnetwork access protocol, the provision of the underlying service assumed by the CLNP is achieved by using the connectionless-mode alternative. 5.2 Subnetwork user data The SN-Userdata is an ordered multiple of octets, and is transferred transparent
48、ly between the specified subnetwork points of attachment. The underlying service assumed by the CLNP is required to support a service data unit size of at least 512 octets. If the minimum service data unit sizes supported by all of the subnetworks involved in the transmission of a particular PDU are
49、 known to be large enough that segmentation is not required, then either the full protocol or the non-segmenting protocol subset may be used. Data received from a subnetwork with protocol identification specifying this protocol (see ITU-T Rec. X.233 I ISOiEC 8473-1) shall be processed according to this Recommendation I International Standard. NOTE - Data with other protocol identification should be ignored, since it may have been sent by an implementation supporting additional protocols intended for use with this protocol. ITU-T Rec. X.625 (1996 E) 3 STD-IT
