1、INTERNATIONAL TELECOMMUNICATION UNION ITU=T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU X.224 (1 1/95) SERIES X: DATA NETWORKS AND OPEN SYSTEM COM M U N I CATI ON Open Systems Interconnection - Connection-mode protocol specifications “i InforAation technology - Open Systems Interconnection - Pro
2、tocol for providing the connection-mode transport service ITU-T Recommendation X.224 (Previously “CCITT Recommendation”) STD-ITU-T RECMN X-224-ENGL 1995 48b2591 Ob22b02 29b ITU-T X-SERIES RECOMMENDATIONS DATA NETWORKS AND OPEN SYSTEM COMMUNICATION PUBLIC DATA NETWORKS Services and facilities X. 1-X.
3、 199 X.l -X. 19 1 Interfaces X.20-X.49 Transmission, signalling and switching Network aspects X. 5 O-X.89 X.90-X.149 Maintenance X.150-X.179 Administrative arrangements X.180-X.199 Model and notation X.200-X.209 Service definitions X.2 10-X.219 Connectionless-mode protocol specification PICS proform
4、as Protocol Identification Security Protocols Layer Managed Objects Conformance testing General Satellite data transmission networks MESSAGE HANDLING SYSTEMS DIRECTORY OS1 NETWORKING AND SYSTEM ASPECTS INTERWORKING BETWEEN NETWORKS Networking Efficiency Naming, Addressing and Registration Abstract S
5、yntax Notation One (ASN.l) Systems Management framework and architecture Management Communication Service and Protocol Structure of Management Information Management functions OS1 MANAGEMENT SECURITY OS1 APPLICATIONS Commitment, Concurrency and Recovery 1 Transaction processing Remote operations OPE
6、N DISTRIBUTED PROCESSING 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.3 00-X.399 X.300-X.349 X.350-X.399 X.400-X.499 X.500-X.599 X.600-X.699 X.600-X.629 X.630-X.649 X.650-X.679 X.680-X.699 X.700-X.799 X.700-X.709 X.710-X.719 X.720-X.729 X.730-X.799 X.800-X.849 X.850-X.89
7、9 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 IT (International Telecommunication Union) is the United Nations Specialized Agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (-T)
8、 is a permanent organ of the ITU. Some 179 member counuies, 84 telecom operating entities, 145 scientific and industrial organizations and 38 international organizations participate in ITU-T which is the body which sets world telecommunications standards (Recommendations). The approval of Recommenda
9、tions by the Members of IT-T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsinki, 1993). In addition, the World Telecommunication Standardization Conference (WTSC), which meets every fou years, approves Recommendations submitted to it and establishes the study programme for the
10、following period. In some areas of information technology which fall within IT-Ts purview, the necessary standards are prepared on a collaborative basis with IS0 and IEC. The text of IT-T Recommendation X.224 was approved on 21st of November 1995. The identical text is also published as ISOAEC Intem
11、ational Standard 8073. NOTE In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. O ITU 1997 All rights reserved. No part of this publication may be reproduced or utilized in any form or
12、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 C. ITU-T Rec. X.224 (1995 E) 1 STD-ITU-T RECMN X-224-ENGL L775 LiBb2571 Ob22bOLi Ob7 1 2 3 4 5 6 7 8 CONTENTS Scope References 2.1 Identic
13、al Recommendations I International Standards 2.2 Definitions Paired Recommendations I Intemational Standards equivalent in technical content Abbreviations . 4.1 Data units 4.2 Types of Transport Protocol data units . 4.3 TPDU fields 4.4 Times and associated variables . 4.5 Miscellaneous . Overview o
14、fthe Transport Protocol . 5.1 Service provided by the Transport Layer 5.2 Service assumed fiom the Network Layer 5.3 5.4 5.5 characteristics of class 4 transport protocol when operating over CLNS 5.6 Elements of procedure Functions of the Transport Layer Classes and options when operating over CONS
15、Model ofthe Transport Layer . 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 6.10 6.1 1 6.12 6.13 6.14 6.15 6.16 6.17 6.18 6.19 6.20 6.2 1 6.22 6.23 Use of the network service Transport Protocol Data Unit (TPDU) transfer . Segmenting and reassembling . Concatenation and separation . Connection establishment .
16、Connection refusal Normal release Error release when operating over CONS . Association of TPDUs with transport connections . Data TPDU numbering . Expedited data transfer . Reassignment after failure when operating over CONS . Resynchronization . Multiplexing and demultiplexing when operating over C
17、ONS Explicit flow control . Checksum Frozen references Retransmission on time-out Resequencing Inactivity control . Treatment of protocol errors . Splitting and recombining when operating over CONS . Retention and acknowledgement of TPDUs . Protocol classes Specification for class O . Simple class .
18、 8.1 Functions of class O . Page 1 1 2 2 2 4 4 4 4 4 5 5 5 5 6 8 10 10 10 11 12 13 13 13 19 20 22 22 25 26 27 28 30 32 32 33 34 34 35 35 35 36 37 37 37 11 8.2 Procedures for class O . 37 ITU-T Rec . X.224 (1995 E) 9 10 11 12 13 14 STD-ITU-T RECMN X.22Li-ENGL 1995 m Li8b2591 Ub22b05 TT5 m Specificati
19、on for class 1 . Basic error recovery class Specification for class 2 . Multiplexing class Specification for class 4 . Error detection and recovery class . Structure and encoding of TPDUs . Specification for class 3 . Error recovery and multiplexing class . 13.1 13.2 13.3 13.4 13.5 13.6 13.7 13.8 13
20、.9 13.10 13.1 1 13.12 Validity . Structure Connection Request (CR) TPDU Connection Conh (CC) TPDU . Disconnect Request (DR) TPDU Disconnect Confirm (DC) TPDU . Data (DT) TPDU . Expedited Data (ED) TPDU . Data Acknowledgement (AK) TPDU . Expedited Data Acknowledgement (EA) TPDU Reject (RI) TPDU . TPD
21、U Error (ER) TPDU . Conformance 14.5 Claims of conformance shall state Annex A . State tables A.l General A.2 Conventions A.3 Tables A.4 State tables for classes O and 2 AS State tables for classes 1 and 3 A.6 State tables for class 4 over CONS . A.7 State tables for class 4 over CLNS Annex B - Netw
22、ork connection management subprotocol . B . 1 B.2 B.3 B.4 B.5 B.6 B.7 B.8 B.9 B.10 B.ll Introduction . Scope . Definitions Abbreviations Overview ofthe protocol Elements of procedure Protocol operation . Structure and encoding of TPDUs Conformance . State table Diagram for NCMS protocol operation An
23、nex C -PICS Proforma c . 1 c.2 c.3 c.4 c.5 C.6 c.7 C.8 c.9 c.10 c.11 General Identification . Indices used in this Annex . Based Recommendation I International Standard conformance General statement of conformance Protocol implementation . NCMS functions . Initiatorhesponder capability for protocol
24、classes O - 4 Supported fnctions Supported TPDUs . Supported parameters of issued TPDUs . Page 39 40 42 43 55 55 55 57 62 62 63 64 65 66 68 68 69 70 71 72 72 72 73 75 78 80 89 92 92 92 92 93 93 94 98 102 104 105 107 110 110 110 111 113 113 113 113 114 114 120 121 . ITU-T Rec . X.224 (1995 E) 111 STD
25、-ITU-T RECMN X-22L1-ENGL 1775 Li8b2571 Db22bOb 731 C.12 Supported parameters for received TPDUs C . 13 User data in issued TPDUs . C.14 User data in received TPDUs C . 15 Negotiation C . 16 Error handling . C.17 Timers and protocol parameters Annex D - Checksum Algorithms . D.l Symbols . D.2 Arithme
26、tic conventions . D.3 Algorithm for generating checksum parameters . D.4 Algorithm for checking checksum parameters Annex E - State tables for operation of class 4 over connection-mode and connectionless-mode network services E.l General E.2 Conventions E.3 Tables E.4 State tables for class 4 . Appe
27、ndix I - Differences between IT-T Rec . X.224 (1993) and ISO/IEC 8073:1992 1.2 Conformance . 1.3 Class negotiation . Difference between IT-T Rec . X.224 and ISO/IEC 8073 1.1 Assignment to network connections . 1.4 Precedence 1.5 Page 128 128 130 130 134 135 137 137 137 137 138 139 139 139 139 139 14
28、7 147 147 147 147 147 iv ITU-T Rec . X.224 (1995 E) Summary This Recommendation International Standard specifies a common encoding and a five classes of transport protocol procedures which provide connection-mode transport service over either connection-mode or connectionless-mode network service an
29、d to be used with different network qualities of service. Introduction This Recommendation I Intemational Standard is one of a set of Recommendations I International Standards produced to facilitate the interconnection of information processing systems. This set of Recommendations I International St
30、andards covers the services and protocols required to achieve such interconnection. The Transport Protocol is positioned with respect to other related Recommendations 1 International Standards by the layers defined in the Reference Model for Open Systems Interconnection (see CCIT Rec. X.200 1 IS0 74
31、98). It is most closely related to, and lies within the field of application of the Transport Service (see ITU-T Rec. X.214 I ISOAEC 8072). It also uses and makes reference to the Network Service Standard (see CCITT Rec. X.213 1 ISOAEC 8348), whose provisions it assumes in order to accomplish the tr
32、ansport protocols aims. The interrelationship of these Recommendations I Intemational Standards is illustrated in Figure Intro. 1. . Transport senice b) different error rates; c) integrity of data requirements; d) reliability requirements. It does not require an implementation to use all of these me
33、chanisms, nor does it define methods for measuring achieved quality of service or criteria for deciding when to release transport connections following quality of service degradation. ITU-T Rec. X.224 (1995 E) V The primary aim of this Recommendation I International Standard is to provide a set of r
34、ules for communication expressed in terms of the procedures to be carried out by peer entities at the time of communication. These rules for communication are intended to provide a sound basis for development in order to serve a variety of purposes, .e.: a) b) c) d) as a guide for implementors and d
35、esigners; for use in the testing and procurement of equipment; as part of an agreement for the admittance of systems into the open systems environment; as a refinement of the understanding of OSI. As it is expected that the initial users of this Recommendation I International Standard will be design
36、ers and implementors of equipment, this Recommendation 1 International Standard contains, in notes or in annexes, guidance on the implementation of the procedures defined herein. It should be noted that, as the number of valid protocol sequences is very large, it is not possible with current technol
37、ogy to verifi that an implementation will operate the protocol defined in this Recommendation I Intemational Standard correctly under all circumstances. It is possible by means of testing to establish confidence that an implementation correctly operates the protocol in a representative sample of cir
38、cumstances. It is, however, intended that this Recommendation I International Standard can be used in circumstances where two implementations fail to communicate in order to determine whether one or both have failed to operate the protocol correctly. This Recommendation 1 International Standard cont
39、ains a clause on conformance of equipment claiming to implement the procedures in this Recommendation I International Standard. To evaluate conformance of a particular implementation, it is necessary to have a statement of which capabilities and options have been implemented for a given OS1 protocol
40、. Such a statement is called a Protocol Implementation Conformance Statement (PICS). A PICS proforma is provided in Annex C. Attention is drawn to the fact that this Recommendation I International Standard does not contain any tests to demonstrate this conformance. The variations and options availab
41、le within this Recommendation I International Standard are essential as they enable a transport service to be provided for a wide variety of applications over a variety of network qualities. Thus, a minimally conforming implementation will not be suitable for use in all possible circumstances. It is
42、 important, therefore, to quaiis. all references to this Recommendation I Intemational Standard with statements of the options provided or required or with statements of the intended purpose of provision or use. vi ITU-T Rec. X.224 (1995 E) STD-ITU-T RECNN X.224-ENGL 1995 m 48b259L Ob22b b40 m ISO/I
43、EC 8073 : 1997 (E) INTERNATIONAL STANDARD ITU-T RECOMMENDATION INFORMATION TECHNOLOGY - OPEN SYSTEMS INTERCONNECTION - PROTOCOL FOR PROVIDING THE CONNECTION-MODE TRANSPORT SERVICE (Malaga-Torremolinos, 1984; amended at Melbourne, 1988, and at Geneva, 1993; revised in 1996) 1 Scope This Recommendatio
44、n I Intemational Standard specifies: a) five classes of procedures when operating over the connection-mode network service: I) class O: simple class; 2) 3) class 2: multiplexing class; 4) 5) for the connection-mode transfer of data and control information from one transport entity to a peer transpor
45、t entity; one class (class 4) of procedure when operating over the connectionless-mode network service; the means of negotiating the class of procedures to be used by the transport entities; the structure and encoding of the transport protocol data units used for the transfer of data and control inf
46、ormation. class 1 : basic error recovery class; class 3 : error recovery and multiplexing class; class 4: error detection and recovery class; b) c) d) The procedures are defined in terms of: i) the interactions between peer transport entities through the exchange of transport protocol data units; ii
47、) the interactions between a transport entity and the transport service user in the same system through the exchange of transport service primitives; iii) the interactions between a transport entity and the network service provider through the exchange of network service primitives. These procedures
48、 are defined in the main text of this Recommendation 1 Intemational Standard supplemented by state tables in Annex A. These procedures are applicable to instances of communication between systems which support the Transport Layer of the OS1 Reference Model and which wish to interconnect in an open s
49、ystems environment. This Recommendation I International Standard specifies, in clause 14, conformance requirements for systems implementing these procedures and provides the PICS profonna in compliance with the relevant requirements, and in accordance with the relevant guidance, given in CCITT Rec. X.291 and ISOAEC 9646-2. It does not contain tests which can be used to demonstrate this conformance. 2 References The following Recommendations and International Standards contain provisions which, through references in this text, constitute provisions of this Recommendat
