1、 ITU-T RECMN*X-235 75 W 4862573 0607267 T26 W INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU DATA NETWORKS AND OPEN SYSTEM COMMUNICATIONS OPEN SYSTEMS INTERCONNECTION - CONNECTIONLESS-MODE PROTOCOL SPECIFICATIONS X.235 (04/95) INFORMATION TECHNOLOGY - OPE
2、N SYSTEMS INTERCONNECTION - CONNECTIONLESS SESSION PROTOCOL: PROTOCOL SPECIFICATION ITU-T Recommendation X.235 (Previously “CCIlT Recommendation”) FOREWORD ITU (International Telecommunication Union) is the United Nations Specialized Agency in the field of telecommunications. The ITU Telecommunicati
3、on 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 38 international organizations participate in ITU-T which is the body which sets world telecommunications standards (Recommenda
4、tions). The approval of Recommendations 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 four years, approves Recommendations submitted to it and estab
5、lishes 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 IT-T Recommendation X.235 was approved on 10th of April 1995. The identical text
6、is also published as ISOAEC International Standard 9548-1. NOTE In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. O ITLJ 1996 All rights reserved. No part of this publication may be r
7、eproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITLJ. ITU-T RECMN*X=235 95 4862573 Ob09273 Li84 m Subject area PUBLIC DATA NETWORKS ITU-T X-SERIES RECOMMENDATIONS DATA NETWORKS AND OPEN SYSTEM C
8、OMMUNICATIONS (February 1994) ORGANIZATION OF X-SERIES RECOMMENDATIONS Recommendation Series Services and Facilities In terfaces x. 1 -x. 19 X.20-X.49 I Transmission, Signalling and Switching I X.50-X.89 I Network Aspects Maintenance X.90-X. 149 X. 150-X. 179 Administrative Arrangements OPEN SYSTEMS
9、 INTERCONNECTION X.180-X.199 Service Definitions Connection-mode Protocol Specifications Connectionless-mode Protocol Specifications X.210-X.219 X.220-X.229 X.230-X.239 I Protocol Identification I X.260-X.269 I Security Protocols Layer Managed Objects Conformance Testing X.270-X.279 X.280-X.289 X.29
10、0-X.299 INTERWORKING BETWEEN NETWORKS General X.300-X.349 Mobile Data Transmission Systems Management MESSAGE HANDLING SYSTEMS DIRECTORY OS1 NETWORKING AND SYSTEM ASPECTS X.350-X.369 X.370-X.399 X.400-X.499 X.500-X.599 I SECURITY I X.800-X.849 I Networking Naming, Addressing and Registration X.600-X
11、.649 X.650-X.679 I Transaction Processing I X. 860-X. 879 I Abstract Syntax Notation One (ASN. 1) OS1 MANAGEMENT X.680-X.699 X.700-X.799 OS1 APPLICATIONS Commitment, Concurrency and Recovery X.850-X.859 Remote Operations OPEN DISTRIBUTED PROCESSING X.880-X.899 X.900-X.999 CONTENTS SECTION 1 . GENERA
12、L . 1 Scope 2 Normative references . Identical Recommendations I International Standards 3 Definitions 3.1 Reference model definitions . 3.2 Additional definitions . 4 Abbreviations . 4.1 Data Units . 4.2 Session protocol data units 4.3 SPDU fields 4.4 Parameters . 4.5 Miscellaneous . Service provid
13、ed by the session layer . Functions of the session layer . Model of the session layer SECTION 2 - CONNECTIONLESS SESSION PROTOCOL SPECIFICATION 6 Protocol mechanisms 6.1 Session protocol data unit (SPDU) transfer 6.2 Connectionless mode transfer . Encoding of the unit data (UD) SPDU . 7.1 TSDU struc
14、ture . 7.2 SPDU structure . 7.3 SPDU identifiers and associated parameter fields 8 Conformance Annex A - State table . 2.1 5 Overview of the connectionless session protocol . Service assumed from the transport layer . 5.1 5.2 5.3 5.4 7 ITU-T RW . X.235 (1995 E) Page i 1 1 1 2 2 2 2 2 2 2 3 3 3 3 3 4
15、 4 4 4 4 5 6 6 6 8 8 9 1 ITU-T RECMN*X*235 95 m 48b259L Ob09273 457 m Summary This Recommendation I International Standard provides the protocol for the OS1 connectionless-mode Session service which is defined in Recommendation X.215. .- ii ITU-T Rec X.235 (1995 E) Introduction The connectionless se
16、ssion protocol specification is one of a set of Recommendations I International Standards produced to facilitate the interconnection of computer systems. The set of standards covers the services and protocols required to achieve such interconnection. The connectionless session protocol specification
17、 is positioned with respect to other related standards by the layers defined in the Reference Model for Open Systems Interconnection (see ITU-T Rec. X.200 I ISO/IEC 7498-1). In particular, it is a protocol of the Session Layer. It is most closely related to the Session Service Definition (see IT-T R
18、ec. X.215 I ISO/IEC 8326) and the Transport Service Definition (see ITU-T Rec. X.214 I ISO/IEC 8072). The interrelationship of these standards is depicted in Figure. The structure of this Recommendation I International Standard is similar to the structure of the connection mode Session Protocol Spec
19、ification (see ITU-T Rec. X.225 I ISO/IEC 8327-1) in order to facilitate cross reference between the two standards. Session Service Definition Connectionless Session t Protocol Specification Transport Service Definition Figure 1ntro.l- Relationship between the connectionless session protocol and adj
20、acent services . ITU-T Rec. X.235 (1995 E) 111 ITU-T RECMNMX.235 95 W 4862573 0609275 22T P INTERNATIONAL STANDARD ITU-T RECOMMENDATION INFORMATION TECHNOLOGY - OPEN SYSTEMS INTERCONNECTION - CONNECTIONLESS SESSION PROTOCOL: PROTOCOL SPECIFICATION SECTION 1 - GENERAL 1 Scope This Recommendation I In
21、ternational Standard specifies: a) procedures for the connectionless transmission of data and protocol control information from one session entity to a peer session entity; b) the encoding of the session protocol data units used for the transmission of data and control information; c) procedures for
22、 the correct interpretation of session protocol control information; and d) the functional requirements for implementations claiming conformance to this Recommendation I International Standard. The procedures are defined in terms of: e) the interactions among peer session entities through the exchan
23、ge of session protocol data units; fj the interactions between a session entity and a session service user through the exchange of session service primitives; and g) the interactions between a session entity and a transport provider through the exchange of transport service primitives. This Recommen
24、dation I International Standard specifies a connectionless session protocol. A connection-oriented session protocol is specified in IT-T Rec. X.225 I ISOAEC 8327-1. 2 Normative references The following Recommendations and International Standards contain provisions which, through reference in this te
25、xt, constitute provisions of this Recommendation I 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 I International Standard are encouraged to inves
26、tigate the possibility of applying the most recent edition of the Recommendations and Standards listed below. Members of IS0 and IEC maintain registers of currently valid International Standards. The Telecommunication Standardization Bureau of the ITU maintains a list of currently valid ITU-T Recomm
27、endations. 2.1 Identical Recommendations I International Standards - * IT-T Recommendation X.200 (1994) I ISO/IEC 7498-1 : 1994, Information technology - Open Systems Interconnection - Basic Reference Model: The Basic Model. IT-T Recommendation X.214 (1993) I ISO/IEC 8072:1994, Information technolog
28、y - Open Systems Interconnection - Transport service definition. - ITU-T Rec. X.235 (1995 E) 1 ITU-T RECMN*X*235 95 YBb259L Ob09277 OT2 ISO/IEC 9548-1 : 1995 (E) - ITU-T Recommendation X.215 (1994) I ISO/IEC 8326: .I, Infomtion technology - Open Systems Interconnection - Session service definition.
29、ITU-T Recommendation X.225 (1994) I ISOAEC 8327-1: .), Informution technology - Open Systems Interconnection - Connection-oriented Session Protocol: Protocol specification. - 3 Definitions 3.1 Reference model definitions This Recommendation I International Standard makes use of the following terms d
30、efined in IT-T Rec. X.200 I ISO/IEC 7498- 1 : a) Transport Layer; b) Session Layer; c) session service access point; d) e) session entity; f) protocol; g) service. session service access point address; 3.2 Additional definitions For the purposes of this Recommendation I International Standard, the f
31、ollowing definitions apply: 3.2.1 instance of session connectionless mode transmission. 3.2.2 instance of session connectionless mode transmission. calling session address: Identifies the session service user that acts as the source of data during a particular caiied session address: Identifies the
32、session service user that acts as the sink of data during a particular 4 Abbreviations 4.1 Data Units For the purposes of this Recommendation I Intemational Standard, the following abbreviations apply: SPDU Session Protocol Data Unit SDU Service Data Unit TSDU Transport Service Data Unit 4.2 Session
33、 protocol data units UD SPDU Unit Data SPDU 4.3 SPDU fields SI SPDU Identifier LI Length Indicator PI Parameter Indicator PV Parameter Value ) To be published. 2 ITU-T RW. X.235 (1995 E) 4.4 4.5 5 5.1 Primitive Parameters - calling session selector; - called session selector. Parameters Miscellaneou
34、s SPM Session Protocol Machine ss Session Service SS-user Session Service User SSAP Session Service Access Point TSAP Transport Service Access Point Overview of the connectionless session protocol Service provided by the session layer The service provided by the protocol described in this Recommenda
35、tion I Ir rrnational Standard is a connectionless session service. The connectionless session service is described in ITU-T Rec. X.215 I ISO/IEC 8326. The session service primitives provided are summarized in Table 1. Table 1 - Connectionless session service primitives Primitive I S-UNIT-DATA reques
36、t S-UNIT-DATA indication Parameters Calling session address Called session address Quality of Service SS-User-Data Calling session address Called session address SS-User-Data 5.2 The session protocol described in this Recommendation I International Standard can operate only over the connectionless t
37、ransport service defined in ITU-T Rec. X.214 I ISO/IEC 8072. When operating over that service, the service primitives summarized in Table 2 are used. Service assumed from the transport layer T-UNIT-DATA request T-UNIT-DATA indication Source address Destination address Quality of Service TS-User-Data
38、 Source address Destination address TS-User-Data NOTE - Only those parameters pertinent to this session protocol are included in the above tables. ITU-T Rec. X.235 (1995 E) 3 ISO/IEC 9548-1 : 1995 (E) 5.3 Functions of the session layer The functions of the session layer are: a) to map session addres
39、ses onto transport addresses; b) c) d) to transfer an SSDU. to select transport Quality of Service parameters needed; to transfer session selectors; and 5.4 Model of the session layer A session protocol entity is comprised of one or more session protocol machines (SPMs). A SPM may be connection orie
40、nted or connectionless. The connectionless session protocol machine communicates with the SS-user through one or more SSAPs by means of the connectionless session service primitives (defined in ITU-T Rec. X.215 I ISOAEC 8326). These session service primitives cause or result from the exchange of SPD
41、Us between peer session entities engaged in connectionless mode transmission. These protocol exchanges are effected by making use of the services of the transport layer, as defined in the transport service definition. The model of session connectionless mode transmission is presented in 6.2 of the s
42、ession service definition covering connectionless mode transmission. The model of the session layer is illustrated in Figure 1. Secsiai Protacol Machine Secsion Protocol Machine I I -(TSAP) . TO721 270-94Id02 Figure 1 - Model of the connectionless session layer SECTION 2 - CONNECTIONLESS SESSION PRO
43、TOCOL SPECIFICATION 6 Protocol mechanisms The protocol mechanisms described below are those used for the connectionless session protocol. 6.1 6.1.1 Purpose To convey session protocol data units in user data fields of transport service primitives. Session protocol data unit (SPDU) transfer 4 IW-T Rec
44、. X.235 (1995 E) ISO/IEC 9548-1 : 1995 (E) 6.1.2 Transport senice primitives The procedure uses the following transport service primitives: T-UNIT-DATA request T-UNIT-DATA indication 6.1.3 SPDUs used The SPDUs defined for the connectionless protocol are listed below: SPDU Name Abbreviation UNITDATA
45、UD 6.2 Connectionless mode transfer 6.2.1 Purpose To transfer one SSDU from one SS-user to another SS-user without session connection establishment or release. 6.2.2 Transport service primitives T-UNIT-DATA request T-UNIT-DATA indication 6.2.3 SPDUs and fields used UD SPDU version number calling ses
46、sion selector called session selector user data 6.2.4 Sending a UD SPDU The called and calling session address parameters of the S-UNIT-DATA request service primitive are used to determine the source address, calling session selector, destination address, and called session selector. If the length o
47、f the SPDU exceeds the maximum TSDU size supported by the transport service, then the S-UNIT-DATA request is discarded and a local report may be made to the SS-user indicating the inability of the session layer to provide the service requested. A UD SPDU is constructed with a calling session selecto
48、r, a called session selector, and user data supplied by the SS- user in the S-UNITDATA request. It also contains a protocol version number provided by the SPM. A T-UNIT-DATA request service primitive is issued with the source and destination addresses determined above, the Quality of Service request
49、ed and a TS-user-data parameter containing the UD SPDU. 6.2.5 Receiving a UD SPDU The UD SPDU arrives in the TS-user-data field of a T-UNIT-DATA indication. A valid incoming UD SPDU results in an S-UNIT-DATA indication, provided that the version number parameter in the incoming UD SPDU indicates at least one protocol version which is supported by the receiving SPM. Parameters corresponding to the highest common protocol version are supplied in the S-UNIT-DATA indication. The source address from the T-UNIT-DATA indication and the calling se
