1、INTERNATIONAL TELECOMMUNICATION UNION ITU=T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU DATA NETWORKS AND OPEN SYSTEM COMMUNICATIONS OPEN SYSTEMS INTERCONNECTION - PROTOCOL IDENTIFICATION X.264 (1 1/93) TRANSPORT PROTOCOL IDENTIFICATION MECHANISM ITU-T Recommendation X.264 (Previously “CCITT Rec
2、ommendation”) FOREWORD The -T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (). The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommen- dations on them with a view to standardizing telecommun
3、ications on a worldwide basis The World Telecommunication Standardization Conference (WTSC), which meets every four years, etablishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. The approval of Recommendations by the Members of the IT
4、U-T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993). IT-T Recommendation X.264 was prepared by ITU-T Study Group 7 (1993-1996) and was approved under the WTSC Resolution No. 1 procedure on the 16th of November 1993. NOTE In this Recommendation, the express
5、ion “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. O IT 1994 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 a
6、nd microfilm, without permission in writing from the ITU. 4862591 O590303 281 = CONTENTS Scope of the Recommendation . References 2.1 Identical Recommendations I International Standards 2.2 2.3 Additional references Definitions Abbreviations . 4.1 Transport protocol data unit 4.2 TPDU fields Use of
7、the network service . Protocol functions 6.1 Default identification 6.2 Explicit identification . Paired Recommendations I International Standards equivalent in technical content 6.3 Protocol operation . Structure and encoding of the UN TPDU 7.1 Structure 7.2 Length indicator (LI) field 7.3 Fixed pa
8、rt 7.4 Variable part . Conformance Annex A . Protocol Implementation Conformance Statement (PICS) Proforma . A.l General A.2 Supported TPDU A.3 Supported parameters of issued TPDU . A.4 A.5 Actions on protocol identification Supported parameters for received UN TPDU . Recommendation X.264 (11/93) Pa
9、ge 1 1 1 1 2 2 2 2 2 2 2 2 2 3 3 3 3 3 4 4 5 5 5 6 6 6 1 m 4862571 0590104 118 SUMMARY This Recommendation defines the transport protocol identification mechanism. The use of a protocol identification procedure allows transport entities to be implemented which can support both the OS1 transport and
10、non-OS1 protocols above the OS1 network layer. INTRODUCTION This Recommendation is one of a set of Recommendations produced to facilitate the interconnection of open systems. The set of Recommendations covers the services and protocols required to achieve such interconnection. The identification mec
11、hanism of transport protocols is positioned with respect to other related Recommendations by the layers defined in the Reference Model for Open Systems Interconnection (see Recommendation X.200). It allows identification of protocols (both OS1 and non-OSI) used on a given network connection. The ini
12、tiating transport entity of a network connection may indicate to the accepting transport entity, what transport protocol is to be used on that network connection. ii Recommendation X.264 (1yP3) 4862593 0590305 054 Recommendation X.264 TRANSPORT PROTOCOL IDENTIFICATION MECHANISMi) (Geneva, 1993) 1 Sc
13、ope of the Recommendation The procedures specified in this Recommendation do not prevent communication between transport entities conforming to ITU-T Recommendation X.224 I ISO/IEC 8073 only and those conforming to ITU-T Recommendation X.2241 ISODEC 8073 as well as to this Recommendation. The use of
14、 a protocol identification procedure allows transport entities to be implemented which can support both the OS1 transport protocols and non-OS1 protocols above the OS1 network layer. NOTE - The use of NSAP addresses as it is defined in CCITT Recommendation X.650 I ISO/IEC 7498-3 provides another pos
15、sibility in distinguishing between OS1 and non-OS1 users of the network service. If however, the use of NSAPs incurs unacceptable penalties, for example where each NSAP is charged for by the network provider, then the transport protocol identification mechanism is available. 2 References The followi
16、ng Recommendations and International Standards contain provisions which through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and Standards are subject to revision, and parties to agreements ba
17、sed on this Recommendation are encouraged to investigate the possibility of applying the most recent edition of the Recommendations and Standards listed below. Members of IEC and IS0 maintain registers of currently valid International Standards, the Telecom- munication Standardization Bureau of the
18、ITU maintains a list of currently valid ITU-T Recommendations. 2.1 Identical Recommendations I Internationai Standards - CCITT Recommendation X.213 (1992) I ISO/IEC 8348: 1992, Information technology - Network service definition for Open Systems Interconnection. ITU-T Recommendation X.2 14 (1993) I
19、ISOAEC 8072: 1993, Information technology - Transport service definition for Open Systems Interconnection. ITU-T Recommendation X.2342) I ISO/IEC 8602 . . .2), Information technology - Protocol for providing the OS1 connectionless-mode transport service. - - 2.2 Paired Recommendations I Internationa
20、l Standards equivalent in technical content - CCITT Recommendation X.200 (1988), Reference model of Open Systems Interconnection for CCITT applications. IS0 7498: 1984, Information processing systems - Open Systems Interconection - Basic Reference Model. ITU-T Recommendation X.224 ( 1993), Protocol
21、for providing rhe OS1 connectionless-mode transport service. ISO/IEC 8073: 1992, Information technology - Telecommut?ications and information exchange between systems - Open Systems Interconnection - Protocol for providing the connection mode transport service. - I) Recommendation X.264 and ISO/IEC
22、1 i 570, information technology - Telecommunications and information exchange between systems - Open Systems Interconnection - Transport protocol identification mechanism, were developed in close collaboration and are technically identical. 2, Presently at the stage of draft. Recommendation X.264 (1
23、1/93) 1 4862593 0590306 T90 - CCITT Recommendation X.650 (1992), Open Systems Interconnection (OS) - Reference model for naming and addressing. IS0 7498-3: 1989, Information processing systems - Open Systems Interconnection - Basic Reference Model - Part 3: Naming and addressing. ITU-T Recommendatio
24、n X.2743), Transport layer security protocol for Open Systems Interconnection. ISOfiEC 10736: 1992, Information technology - Telecommunications and information exchange between systems - Transport layer security protocol. - 2.3 Additional references - ITU-T Recommendation X.25 (1993), Interface betw
25、een data terminal equipment (DTE) and data circuit-terminating equipment (DCE) for terminals operating in the packet mode and connected to public data networks by dedicated circuit. CCITT Recommendation X.244 (1988). Procedure for the exchange of protocol identification during virtual call establish
26、ment on packet switched public data networks. - 3 Definitions The following terms are used by this Recommendation and are defined by CCITT Recommendation X.200 I IS0 7498: - Open Systems Interconnection (OSI); - network connection; - transport entity. 4 Abbreviations 4.1 Transport protocol data unit
27、 UN TPDU Use of network connection TPDU 4.2 TPDU fields LI Length indicator (field) SHARE Sharing option (field) PRT-ID Protocol identifier (field) 5 Use of the network service Transport protocol identification makes use of the network service defined in CC Recommendation X.213 I ISO/IEC 8348. It us
28、es the NS-user data parameter of the N-CONNECT request and indication primitive only. 6 Protocol functions 6.1 Default identification When using default identification, no NS-user data parameter shall be placed in the N-CONNECT request primitive. ITU-T Recommendation X.224 I ISO/IEC 8073 is then ide
29、ntified. 3) Presently at the stage of draft. 2 Recommendation X.264 (1Yg3) 4Bb259L 0590107 927 UN oooOOOO1 LI 6.2 Explicit identification When using explicit identification, an UN TPDU shall be placed in the NS-user data parameter of the N-CONNECT request primitive. This UN TPDU may be followed by o
30、ther PDUs, which are recognizable by the identified protocol, in the NS-user data parameter of the N-CONNECT request primitive. Variable Part PRT-ID SHARE The sending transport entity shall a) b) c) NOTE - This Recommendation does not include procedures for sharing a network connection between diffe
31、rent protocols. a) b) set the PRT-ID field of the UN TPDU to the value assigned in 7.3 to the protocol used; set the SHARE field of the UN TPDU to the value oo00 O000 (no sharing); not use the variable part of the UN TPDU. The following strategies could be used in the future: sequential reuse of a n
32、etwork connection by several protocols (Le. consecutive sharing); concurrent use of a network connection by several protocols (Le. concurrent sharing). Inclusion of these strategies will use other values of the SHARE field and may make use of the variable part of the UN TPDU. 6.3 Protocol operation
33、The receiving transport entity shall operate the protocol, identified either by default or explicitly, if it is claimed that this protocol is supported. Otherwise the network connection shall be refused. 7 Structure and encoding of the UN TPDU The length of the UN TPDU shall not exceed 32 octets. NO
34、TE - This is a restriction imposed on future enhancements to this TPDU by constraints within the Network Layer. This restriction on the length of the parameter is due to the desire not to conflict with the protocol identifier field camed by X.25 CALL REQUEST/INCOMING CALL packets. This is a single o
35、ctet located at the same position as the length indicator of the UN TPDU when the latter is camed in an X.25 CALL REQUEST/INCOMING CALL packet. ITU-T has already chosen values for this parameter and thus it is important not to use those values (see CCITT Recommendation X.244). 7.1 Structure 1 2 3 4
36、5 top 7.2 Length indicator (LI) field The field is contained in the first octet of the TPDUs. The length is indicated by a binary number, with a maximum value of 254 (1 11 1 11 10). The length indicated shall be the header length in octets including parameters, but excluding the length indicator fie
37、ld and user data, if any. The value 255 (1 Il 1 11 1 I) is reserved for possible extensions. If the length indicated exceeds or is equal to the size of the NS-user data which is present, this is a protocol error. 7.3 Fixed part The fixed part shall be as follows: a) UN: UN TPDU code l; Recommendatio
38、n X.264 (1Yg3) 3 4852571r 0570308 863 R PRT-ID LIST 1101 1111 b) PRT-ID: protocol identifier. Values: mm Reserved m o001 m 0010 moo11 ITU-T Recommendation X.274 I ISO/IEC 10736 in conjunction with CC m O100 ITU-T Recommendation X.274 I ISO/IEC 10736 in conjunction with CCITT m O101 through o111 1111
39、 1OOO 1111 1111 CCITT Recommendation X.224 I ISOAEC 8073 ITU-T Recommendation X.234 I ISOAEC 8602 Recommendation X.224 I ISOAEC 8073 Recommendation X.234 I ISOAEC 8602 Reserved for other OS1 protocols through Reserved for private use. NOTE -The code “oo00 0010” is also currently being used to identi
40、fy telematic terminals within the ITU c) SHARE: sharing strategy Values: moooo No sharing Values LENGTH 1 to26 7.4 Variable part The variable part consists of one optional parameter. This parameter is only present when SHARE is different from moooo. 1 2 3 to p TYPE = PRT-ID LIST (1 101 11 1 I), LENG
41、TH = number of PRT-IDS, Value = list of PRT-IDS, one per octet. 8 Conformance A system claiming to conform to this Recommendation shall comply with the requirements of 6.1 and 6.2. 8.1 When initiating a network connection a transport entity shall either a) b) not use the NS-user data parameter of N-
42、CONNECT request primitive and operate using the protocol of ITU-T Recommendation X.224 I ISOAEC 8073 on this network connection; or include a UN TPDU in the NS-user data parameter of the N-CONNECT request primitive and operate using the transport protocol specified in the PRT-ID parameter of the UN
43、TPDU. 8.2 When processing an N-CONNECT indication, a transport entity shall: a) b) regard ITU-T Recommendation X.224 I ISOAEC 8073 as being identified if no UN TPDU is present; or accept the PRT-ID field of the UN TPDU if the UN TPDU is present, and operate the identified protocol if it is claimed t
44、hat this protocol is supported, otherwise reject the network connection. 4 Recommendation X.264 (1U93) Annex A4) Index STI ST2 ST3 Protocol Implementation Conformance Statement (PICS) Proforma (This annex forms an integral part of this Recommendation) TPDU Status support Reference (subclause) Yes No
45、 PI :o NOT PI:M UN supported on transmission 6.2 UN transmitted, when identifying ITU-T Rec. X.224 I ISOAEC 8073 UN supported on receipt 6.3 M Yes 6.2,6.1 STI:O Yes No N/A A.l General A.l.l Symbols used Status symbols: M Mandat o ry O Support symbols: Yes Supported No Not supported NIA Not applicabl
46、e Optional to implement. If implemented the feature may or may not be used A.1.2 The main part of the PICS proforma is a fixed-format questionnaire divided into a number of clauses. Answers to the questionnaire are to be provided in the rightmost column either by simply marking an answer to indicate
47、 a restricted choice (such as Yes or No) or by entering a value of a range of values or entering what action is taken. Instructions for completing the PICS proforma A.2 Supported TPDU 4, Copryright release for PICS proforma. Users of this Recommendation may freely reproduce the PICS proforma in this
48、 annex so that it can be used for its intended purpose and may further publish the completed PICS. 5 Recommendation X.264 (11/93) = 4862571 0590110 411 Index A.3 Supported parameters of issued TPDU Supported parameters 7.3 b) 7.3 c) I Reference (subclause) ITU-T Rec. X.224 I ISOIIEC 8073; ITU-T Rc.
49、X.234 I ISO/IEC 8602; ITU-T Rw. X.274 I ISOIIEC 10736 ITU-T Rw. X.224 I ISOIIEC 8073; ITU-T RC. X.274 I ISOIIEC 10736 in conjunction with in conjunction with ITU-T Rec. X.234 I ISOIIEC 8602; Private: IooOO, ., 1111 1111 No sharing Allowed values RU1 Protocol identifier A.4 Supported parameters for received UN TPDU PI1 Reference I (subclause) Supported parameters I Index Absence of a UN “DU in an N-CONNECT indication is regarded as identifying ITU-T Rw, X.224 I ISOIIEC 8073 PI2 PI3 7.3 b) Operate the identified protocol 6. i, 6.3 P2: M Yes Refuse the network connec
