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FOREWORD tu (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 ne 179 member countries. 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 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 meets 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-T's purview, the necessary standards are prepared on a collaborative basis with Iso and IEC. The text of ITU-t Recommendation X224 was approved on 21st of November 1995. The identical text is also published as Iso/IEC International Standard 8073 NOTE In this recommendation, the expression"Administrationis used for conciseness to indicate both a telecommu dministration and a recognized operating agene CITU 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 C ITU-TRec. X 224(1995E) CONTENTS Page Refere 2. 1 Identical Recommendations International Standards 2. 2 Paired Recommendations International Standards equivalent in technical content Definitions 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 of the transport protocol 5. 1 Service provided by the Transport Layer. 5.2 Servicc assumed from the Network Layer 5.3 Functions of the Transport Layer 5.4 Classes and options when operating over CONS 5.5 Characteristics of class 4 transport protocol when operating over CLNS 5.6 Model of the Transport Layer Elements of procedure . 6.1 Use of the network service 12 6.2 Transport Protocol Data Unit (TPDu)transfer. 111 6.3 Segmenting and reassembling 6.4 Concatenation and separation 6.5 Connection establishment 6. 6 Connection refusal 6.7 Normal release 6.8 Error release when operating over CONS 6.9 Association of TPDUs with transport connections 22222 6.10 Data TPDU numbering 6. 11 Expedited data transfer.... 6. 12 Reassignment after failure when operating over CONS 30 6. 13 Retention and acknowledgement of Tpdu 6. 14 Resynchronization 6. 15 Multiplexing and demultiplexing when operating over CONS 6. 16 Explicit flow control 6. 17 Checksum 6. 18 Frozen references 6. 9 Retransmission on time-out 3333333 6.20 Resequencing.. 6.21 Inactivity control 6.22 Treatment of protocol errors 6.23 Splitting and recombining when operating over CONs 7 Protocol classes… 8 Specification for class 0-Simple class 8. 1 Functions of class o ““ 8. 2 Procedures for class o 4444 ITU-TRec. X.224(1995E) Specification for class 1 Basic error recovery class 10 Specification for class 2- Multiplexing class 40 11 Specification for class 3- Error recovery and multiplexing class 12 Specification for class 4- Error detection and recovery class..... 13 Structure and encoding of TPDUs 13.1 Validity 13.2 Structure 13.3 Connection Request (CR) TPDU 13. 4 Connection Confirm(CC)TPDU 13.5 Disconnect Request (DR)TPDU 13.6 Disconnect Confirm(DC)TPDU 13.7Data(DT)TPDU........... 13.8 Expedited Data(ED)TPDU....,... 5666666 13.9 Data Acknowledgement(AK) TPDU 13. 10 Expedited Data Acknowledgement (EA) TPDU.... 13.11 Reject(RJ)TPDU…… 13. 12 TPDU Error(ER)TPDU. 14 Conformance 14.5 Claims of conformance shall state Annex a-State tables A1 General A2 Conventions A 3 Tables A 4 State tables for classes o and 2 A.5 State tables for classes 1 and 3 单,::·中·;.··中·.·中中中,主 A 6 State tables for class 4 over CONs A 7 State tables for class 4 over CLNs Annex B- Network connection management subprotocol B. 1 Introduction . 2 Scope.. B3 Definitions B 4 Abbreviations B5 Overview of the protocol B6 Elements of procedure B7 Protocol operation 106 B 8 Structure and encoding of TPDUs...... B9 Conformance B 10 State table 113 B 11 Diagram for Ncms protocol operation 115 Annex- Pics Proforma l10 C 2 Identification l10 C 3 Indices used in this annex C 4 Based Recommendation International Standard conformance 113 C 5 General statement of conformance 113 C6 Protocol implementation C 7 NCMS functions 113 C 8 Initiator/responder capability for protocol classes 0-4 C9 Supported functions 114 C 10 Supported TPDUs.. 120 C11 Supported parameters of issued TPDU ITU-TRec. X 224(1995E) Pc C.12 Supported parameters for received TPDUS……….… C 13 User data in issued TPDUs C 14 User data in received tpdus C.15 Negotiation.… 130 C.16 Error handling… 134 C 17 Timers and protocol parameters Annex D-Checksum Algorithms D.1 Symbols.… 137 D2 Arithmetic conventions D 3 Algorithm for generating checksum parameters 137 D 4 Algorithm for checking checksum parameters Annex E-State tables for operation of class 4 over connection-mode and connectionless-mode network services 13 E1 Gene E 2 Conventions E 3 Tables E 4 State tables for class 4 39 Appendix I-Differences between ITU-T Rec X224(1993)and ISO/IEC 8073: 1992......147 I 1 Assignment to network connections 147 L2 Conformance 47 1. 3 Class negotiation 47 L 4 Precedence 47 1.5 Difference between ITU-T RecX224 and ISO/IEC 8073 147 IRec.xX.224(1995E) 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 and to be used with different network qualities of service. Introduction This Recommendation International Standard is one of a set of Recommendations International Standards produced to facilitate the interconnection of information processing systems. This set of Recommendations International Standards covers the services and protocols required to achieve such interconnection The Transport Protocol is positioned with respect to other related Recommendations International Standards by the layers defined in the Reference Model for Open Systems Interconnection(see CCITT Rec X 200 ISO 7498). It is most closely related to, and lies within the field of application of the transport Service (see ITU-T Rec. X 214 ISO/EC 8072). It also uscs and makes refcrence to the Network Scrvice Standard (scc CCITT Rcc. X 213 ISO/EC 8348), whose provisions it assumes in order to accomplish the transport protocols aims. The interrelationship of these Recommendations International Standards is illustrated in Figure Intro. I Transport service definition Transport -Reference to aims- Protocol Specification Reference to assumptions Network service definition T0719300-94/d01 Figure Intro. 1-Relationship between the Transport Protocol and adjacent services This Recommendation International Standard specifies a common encoding and a number of classes of transport protocol procedures to be used with different nctwork qualities of scrvice It is intended that the Transport Protocol should be simple but general enough to cater for the total range of Network Service qualities possible, without restricting future extensions The protocol is structured to give rise to classes of protocol which are designed to minimize possible incompatibilities and implementation costs The classes are selectable with respect to the Transport and Network Services in providing the required quality of service for the interconnection of two session entities(each class provides a different set of functions for enhancement of service qualities This Recommendation International Standard defines mechanisms that can be used to optimize network tariffs and enhance the following qualities of service a) different throughput b) different error rates c) integrity of data requirements d) reliability requirements It does not require an implementation to use all of these mechanisms, 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-TRec. X 224(1995E) The primary aim of this Recommendation International Standard is to provide a set of rules 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, i.e a) as a guide for implementors and designers; b) for use in the testing and procurement of equipment c) as part of an agrecment for the admittance of systems into the open systems environment d) as a refinement of the understanding of OSI As it is expected that the initial users of this Recommendation International Standard will be designers and implementors of equipment, this Recommendation International Standard contains, in notes or in annexes, guidance on the implementation of the procedures defincd herein It should be noted that, as the number of valid protocol sequences is very large, it is not possible with current technology to verify that an implementation will operate the protocol defined in this Recommendation International 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 circumstances. It is, however, intended that this Recommendation 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 International Standard contains a clause on conformance of cquipment claiming to implement the procedures in this Recommendation 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 OSi protocol. 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 International Standard does not contain any tests to demonstrate this conformance The variations and options available within this recommendation 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 important, therefore, to qualify ill references to this Recommendation International Standard with statements of the options provided or required or with statements of the intended purpose of provision or use. TU-T Rec X.224(1995 ISO/IEC8073:1997(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) Scope This Recommendation International Standard specifies a) five classes of procedures when operating over the connection-mode network service 1)class 0: simple class 2) class 1: basic error recovery class 3) class 2: multiplexing class 4 class 3: error recovery and multiplexing class 5)class 4: error detection and recovery class for the connection-mode transfer of data and control information from one transport entity to a peer transport entity, b) one class(class 4 )of procedure when operating over the connectionless-mode network service c) the means of negotiating the class of procedures to be used by the transport entities d) the structure and encoding of the transport protocol data units used for the transfer of data and control information The procedures are defined in terms of i the interactions between peer transport entities through the exchange of transport protocol data units ii) the interactions between a transport entity and the transport service user in the same system through the change of tra t service primitives the interactions between a transport entity and the network service provider through the exchange of network service primitives These procedures are defined in the main text of this recommendation International Standard supplemented by state the OSI Reference Model and which wish to interconnect in an open systems environmert upport the Transport layer of These procedures are applicable to instances of communication between systems which This Recommendation International Standard specifies, in clause 14, conformance requirements for systems mplementing these procedures and provides the pics proforma in compliance with the relevant requirements, and in accordance with the relevant guidance, given in CCITT Rec. X 291 and ISo/EC 9646-2. It does not contain tests which an be used to demonstrate this conformance References The following Recommendations and International Standards contain provisions which, through references in this text, constitute provisions of this recommendation International Standard. At the time of publication, the editions indicated were valid. All Recommendations and Standards are subject to revision, and parties to agreements based on this Recommendation International Standard are encouraged to investigate the possibility of applying the most recent edition of the recommendations and Standards listed below. Members of IEC and IsO maintain registers of currently valid International Standards. The Telecommunication Standardization Bureau of the ITU maintains a list of currently valid Itu-t recommendations ITU-TRec. X 224(1995E) ISO/EC8073:1997E) 2.1 Identical Recommendations International Standards CCITT Recommendation X 213(1992) ISO/IEC 8348: 1993, Information technology-Open Systems Interconnection- Network service definition ITU-T Recommendation X214(1993 ISO/IEC 8072: 1994, Information technology-Open Systems Interconnection Transport service definition 2.2 Paired Recommendations International Standards equivalent in technical content CCITT Recommendation X 200(1988), Reference model of Open Systems Interconnection for CCITTapplications ISO 7498: 1984, Information processing systems-Open Systems Inter connection- Basic Referenc Model ITU-T Recommendation X. 264(1993), Transport protocol identification mechanism ISO/EC 11570: 1992, Inormalion lechnology-Telecommuniculions and information exchange belween systems-Open Systems Interconneclion-Trunsport protocol idenlificalion mechanism CCITT Recommendation X 290(1992),OS/ Conformance testing methodology and framework for protocol Recommendations for CCITT applications-General concepts ISO/EC 9646-1: 1994, Information technology-Open Systems Interconnection- Conformance testin methodology and framework- Part 1: General concepts CCITT Recommendation X291(1992), OS/ conformance testing methodology and framework for protocol Recommendations for CCItT applications- Abstract test suite specification ISO/EC 9646-2: 1994, Information technology-Open Systems Interconnection- Conformance testing methodology and framework Part 2: abstract Test Suite specification CCITT Recommendation X650(1992), Open Systems Interconnections (OSI-Reference Model for naming and addressing ISo 7498-3: 1989, Information processing systems Open Systems Interconnection Basic Reference Model- Part 3: Naming and addressing Definitions NOTE- The definitions contained in this clause make use of abbreviations defined in clause 4 3. This Recommendation International Standard is based on the concepts developed in CCiTT Rec. X200 and ISo 7498 and CCITT Rec. X650 and ISO/EC 7498-3 and makes usc of the following terms defined in them a) concatenation and separation b) segmenting and reassembling, c) multiplexing and demultiplexing; 0 splitting and recombining e) flow control f) connectionless-mode transmission g) transport selector h) nil selector value 3.2 For the purposes of this recommendation, the following definitions apply 3. 2.1 equipment: Ilardware or software or a combination of both; it need not be physically distinct within a computer system 3. 2. 2 transport service user: An abstract representation of the totality of those entities within a single system that make use of the transport service 3.2.3 network service provider: An abstract machine that models the totality of the entities providing the network service, as viewed by a transport entity 3.2.4 local matter: A decision made by a system concerning its behaviour in the transport layer that is not subject to the requirements of this protocol 3.2.5 initiator: a transport entity that initiates a CR-TPdU TU-TRee.x.224(1995E)

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