1、INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU X.623 (07/94) DATA NETWORKS AND OPEN SYSTEM COM M U N I CATI ON S OS1 NETWORKINGS AND SYSTEM ASPECTS - NETWORKING INFORMATION TECHNOLOGY - THE CONNECTIONLESS-MODE NETWORK PROTOCOL FOR PROVIDING SERVICE: PROVI
2、SION OF THE UNDERLYING SERVICE BY A SUBNETWORK THAT PROVIDES THE OS1 DATA LINK SERVICE ITU-T Recommendation X.623 (Previously “CCITT Recommendation”) FOREWORD IT (International Telecommunication Union) is the United Nations Specialized Agency in the field of telecommunications. The IT Telecommunicat
3、ion 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 (Recommend
4、ations). 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 est
5、ablishes 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 Recommendation X.623 was approved on Ist of July 1994. The identical text
6、 is also published as ISODEC International Standard 8473-4. NOTE In this Recommendation. the expression “Administration” is used for conciseness to indicate both a telecornmunication administration and a recognized operating agency. O ITU 1994 All rights reserved. No part of this publication may be
7、reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm. without permission in writing from the ITU. ITU-T X-SERIES RECOMMENDATIONS DATA NETWORKS AND OPEN SYSTEM COMMUNICATIONS (February I994 ORGANIZATION OF X-SERIES RECOMMENDATIONS Subject
8、area PUBLIC DATA NETWORKS Recommendation series Services and facilities Interfaces X. I-X. I9 X.20-X.49 Transmission. signalling and switching Network aspects I OPEN SYSTEMS INTERCONNECTION I I X.50-X.89 X.90-X. 149 I Model and notation Maintenance Administrative arrangements - I200-X209 I x. 150-x.
9、 179 X. I 80-X. 199 I Service definitions I x.2 1 o-x.2 I9 I Connection-mode protocol specifications Connectionless-mode protocol specifications X.220-X.229 X.230-X.239 PICS proformas Protocol identification I Security protocois - X.240-X.259 X.260-X.269 I I X.270-X.279 _ - . _ General x.300-x.349 M
10、obile data transmission systems X.350-X.369 I Layer managed objects I X.280-X.289 I Management MESSAGE HANDLlNG SYSTEMS I Conformance testing x.370-x.399 x.400-x.499 X.290-X.299 I DIRECTORY OS1 NETWORKING AND SYSTEM ASPECTS I INTERWORKING BETWEEN NETWORKS I I x.500-x.599 Networking Naming, addressin
11、g and registration X.600-X.649 X.650-X.679 Abstract Syntax Notation One (ASN.1) OS1 MANAGEMENT X.680-X.699 x .700-x .799 OS1 APPLICATIONS Commitment. concurrency and recovery I SECURITY X.850-X.859 I X.800-X.849 Transaction processing Remote operations X.860-X.879 X.880-X.899 OPEN DISTRIBUTED PROCES
12、SING x.900-x.999 I I CONTENTS Introduction . scope Normative references . 2 .I 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 definitions . 3.2 3.3 3.4
13、 Data link service definitions . Abbreviations . Subnetwork dependent convergence function 5 .i General model . 5.2 Subnetwork user data 5.3 Subnetwork dependent convergence functions used with subnetworks that provide the OS1 data link service Network layer architecture definitions Network layer ad
14、dressing definitions . Annex A . PICS proforma A . 1 Introduction . A.2 Abbreviations and special symbols . A.3 Instructions for completing the PICS proforma A.4 Identification . AS Major capabilities A.6 Subnetwork dependent convergence functions for use with subnetworks that provide the OS1 connec
15、tionless Data Link service A.7 Subnetwork dependent convergence functions for use with subnetworks that provide the OS1 connection-mode Data Link service . Page iii 1 1 1 1 1 2 2 2 2 2 2 3 3 3 9 9 ITU-T RC . X.623 (1994 E) i 1 Summary This Recommendation I International Standard specifies the mappin
16、g between a subnetwork which provides the OS1 data link service and the Connectionless Layer Network Layer service assumed by the Connectionless Layer Network Layer Protocol as defined in Recommendation X.233. II ITU-T RC. X.623 (1994 E) Introduction This is one of a set of Recommendations and Inter
17、national Standards produced to facilitate the interconnection of open systems. The set covers the services and protocols required to achieve such interconnection. This Recommendation I International Standard is positioned with respect to other related Recommendations and International Standards by t
18、he layers defined in ITU-T Rec. X.200 I ISO/IEC 7498- 1. In particular. it defines the way in which an X.25 subnetwork may be used within the Network layer to provide the abstract underlying service with respect to which the protocol defined by ITU-T Rec. X.233 I ISO/IEC 8473- 1 is specified. In ord
19、er 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 have been implemented. Such a statement is called a Protocol Implementation Conformance Statement (PICS), as defined in CCIT Rec. X.2
20、90 I ISO/IEC 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 normative Annex A. . ITU-T Rec. X.623 (1994 E) 111 INTERNATIONAL STANDARD ITU-T RECOMMENDATION INFORMATION TECHNOLOGY - PROTOCOL FOR
21、PROVIDING THE CONNECTIONLESS-MODE NETWORK SERVICE: PROVISION OF THE UNDERLYING SERVICE BY A SUBNETWORK THAT PROVIDES THE OS1 DATA LINK SERVICE 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
22、ISO/IEC 8473-1 is provided by a subnetwork that provides the OS1 Data Link service defined by CC Rec. X.212 I ISO/IEC 8886. 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 pr
23、oforma for this protocol. in compliance with the relevant requirements. and in accordance with the relevant guidance, given in CCITT Rec. X.290 I ISO/IEC 9646-1. 2 Normative references The following Recommendations and International Standards contain provisions which. through reference in this text,
24、 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 10 investig
25、ate the possibility of applying the most recent editions of the Recommendations and Standards listed below. Members of IEC and IS0 maintain registers of currently valid International Standards. The Telecommunication Standardization Bureau of the iTU maintains a list of currently valid IT-T Recommend
26、ations. 2.1 Identical Recommendations I International Standards - ITU-T Recommendation X.200 ( I 994) I ISO/IEC 7498- i : 1994, Information rechnology - Open Sysrems Interconnection - Basic Reference Model. CCITT Recommendation X.213 (1992) I ISOLEC 8348: 1993. Information technology - Network servi
27、ce definition for Open Systems Interconnection. - 2.1 Paired Recommendations I International Standards identical in technical content - CCITT Recommendation X.290 (1992), OS1 conformance testing methodology and framework for protocol Recommendations for CCl7T applications - General concepts. ISOAEC
28、9646- 1 : 199 1, Information technology - Open Systems Interconnection - Conformance testing methodology and framework - Pan I: General concepts. CCITT Recommendation X.212 (1988). Data link service definition for Open Systems Interconnection for CCIT applications. ISOLEC 8886: i 992, Infornution te
29、chnology - Telecommunications and information exchange between systems - Data link service definition for Open Systems Interconnection. - 2.3 Additional references - ISOLEC 8648: 1988, Information processing systems - Open Systems Interconnection - Internal organization of the network layer. ITU-T R
30、ec. X.623 (1994 E) 1 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 I ISOAEC 7498- I a) network entity; b) Network layer; c) Data link layer; d) service; e) service data unit; f) data link servic
31、e; g) protocol control information. 3.2 Network layer architecture definitions This Recommendation I International Standard makes use of the following terms defined in ISO/IEC 8648: a) subnetwork; b) suhnetwork dependent convergence protocol: c) subnetwork dependent convergence function; d) subnetwo
32、rk 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 ISOIIEC 8348: - subnetwork point of attachment. 3.4 Data link service definitions This Recommendation I International Standard makes
33、 use of the following terms defined in CCITT X.212 I ISOIIEC 8886: a) b) data link connection. data link service access point address: 4 Ab brevia tions CLNP Connectionless-mode network protocol DL Data link layer DLSDU Data link layer service data unit PDU Protocol data unit QOS Quality of service
34、SDU Service data unit SN Subnetwork SNDCF Subnetwork dependent convergence function SNDCP Subnetwork dependent convergence protocol SNICP Subnetwork independent convergence protocol SNAcP Subnetwork access protocol SNPA Subnetwork point of attachment SNCR Subnetwork connection reference SNSDU Subnet
35、work service data unit 2 ITU-T Rec. X.623 (1994 E) STD-ITU-T RECMN X.bZ3-ENGL L77i W i8b2592 Ob2043b T22 W ISOREC 8473-4 : 1995 (E) 5 Subnetwork dependent convergence function 5.1 General model The general model for providing the underlying service assumed by the protocol in conjunction with a real
36、subnetwork that uses a connectionless subnetwork access protocol is as follows. The generation of an SN-UNITDATA Request by the CLNP results in the generation of a corresponding subnetwork-specific UNITDATA request by the subnetwork dependent convergence function. The receipt of a subnetwork-specifi
37、c UNITDATA indication associated with delivery of a connectionless data unit to its destination causes the SNDCF to generate an SN-UNITDATA Indication to the CLNP. The general model for providing the underlying service assumed by the CLNP in conjunction with a real subnetwork that uses a connection-
38、mode subnetwork access protocol is as follows. The generation of an SN-UNITDATA Request by the CLNP causes a connection (logical channel. logical link, or the equivalent) to be made available for the transmission of SN-User-data. If a connection cannot be made available, the SN-UNITDATA Request is d
39、iscarded. The receipt of subnetwork-specific PDUs containing SN-User-data causes the SNDCF to generate an SN-UNITDATA Indication to the CLNP. Where a real subnetwork is designed to use either a connectionless-mode or a connection-mode subnetwork access protocol, the provision of the underlying servi
40、ce assumed by the CLNP is achieved by using the connectionless-mode alternati ve. 5.2 Subnetwork user data The SN-Userdata is an ordered multiple of octets. and is transferred transparently between the specified subnetwork points of attachment. The underlying service assumed by the CLNP is required
41、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 known to be large enough that segmentation is not required. then either the full protocol or the non-segmenting
42、protocol subset may be used. Data received from a subnetwork with protocol identification specifying this protocol (see ITU-T Rec. X.233 I ISO/IEC 8473- I ) shall be processed according to this Recommendation I International Standard. NOTE - Data with other protocol identification should be ignored,
43、 since it may have been sent by an implementation supporting additional protocols intended for use with this protocol. 5.3 Subnetwork dependent convergence functions used with subnetworks that provide the OS1 data link service This subclause defines a mapping of the OS1 Data Link service to the unde
44、rlying service assumed by ITU-T Rec. X.233 I ISO/IEC 8473-1. The OS1 Data Link service definition defines two types of Data Link service: a connectionless service and a connection-mode service. SNDCFs are defined for subnetworks that provide either of these two modes of service. 5.3.1 The primitives
45、 defined for provision of the underlying service assumed by the CLNP map directly onto the UNITDATA Request and Indication primitives defined for the connectionless Data Link service. Subnetwork dependent convergence functions perform a mapping of the connectionless Data Link service onto the underl
46、ying service assumed by the CLNP. The mapping is as follows. The generation of an SN-UNITDATA request by the CLNP results in the generation of a DL-UNITDATA request (as described in CCITT Rec. X.212 I ISO/IEC 8886) by the subnetwork dependent convergence function. A corresponding DL-UNITDATA indicat
47、ion prompts the SNDCF to generate an SN- UNITDATA indication to the CLNP. No explicit subnetwork dependent convergence protocol control information is exchanged between Network entities to provide this mapping of service. The parameters of the SN-UNITDATA primitives are mapped onto the DL-UNITDATA p
48、rimitives as follows. The SN-Destination-Address and SN-Source-Address parameters are conveyed in the DL-Destination-Address and DL-Source-Address parameters, respectively. The addresses used in the SN-UNITDATA request and indication primitives are the Data Link service access point addresses descri
49、bed in CCIT Rec. X.212 I ISO/IEC 8886. The SN-Quality-of-Service parameter is conveyed. The available QOS is known prior to the issuance of the DL-UNITDATA request. There is no discrimination among DLSDUs. The SN-Userdata parameter is conveyed in the DL-Userdata parameter. The subnetwork must be able to support the service data unit requirements defined in 5.2. SNDCF used with the connectionless Data Link service ITU-T Rec. X.623 (1994 E) 3 ISO/IEC 8473-4 : 1995 (E) 5.3.2 The primitives defined for pr
