ITU-T X 223-1993 Use of X 25 to Provide the OSI Connection-Mode Network Service for ITU-T Applications - Data Networks and Open System Communications Open Systems Interconnection-G.pdf

1、 STD.ITU-T RECMN X.223-EMGI- 1993 m 48b259L b25738 UT4 D INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU X.223 (I I /93) DATA NETWORKS AND OPEN SYSTEM COMMUNICATIONS OPEN SYSTEMS INTERCONNECTION-GENERAL USE OF X.25 TO PROVIDE THE OS1 CONNECTION-MODE NETWOR

2、K SERVICE FOR ITU-T APPLICATIONS ITU-T Recommendation X.223 (Previously “CCITT Recommendation”) FOREWORD The IT-T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (IT). The IT-T is responsible for studying technical, operating and tariff qu

3、estions and issuing Recommen- dations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the . topics for study by the IT-T Study Groups which, in their turn, produce R

4、ecommendations on these topics. The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993). IT-T Recommendation X.223 was revised by IT-T Study Group 7 (1993-1996) and was approved under the WTSC Resolution

5、No. 1 procedure on the 16th of November 1993. NOTE In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. O ITU 1994 All rights reserved. No part of this publication may be reproduced or u

6、tilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. STD-ITU-T RECMN X.223-ENGL 1773 M L18b2571 Ob25740 752 CONTENTS Page O Introduction 1 1 Scope 2 2 Normative References 2 2.1 Identical Recommendations I In

7、ternational Standards 3 Paired Recommendations I International Standards Equivalent in Technical Content . 2.2 3 2.3 Additional References . 3 3 Definitions 3 3.1 Reference Model Definitions 3 3.2 Service Conventions Definitions 3 3.3 Network Service Definitions . 4 3.4 X.25 Definitions 4 3.5 X.96 D

8、efinitions 4 . 4 Abbreviations . 4 4.1 Network Service Abbreviations 4 4.2 X.25 Abbreviations . 5 5 Overview 5 Elements of the X.25 1 PLP Used to Support the OS1 CONS . 5 General Operation of the X.25 I PLP for Supporting the OS1 CONS . 7 6 Network Connection Establishment Phase . 7 6.1 PrimitivePar

9、ameter and PacketField Relationships 7 6.2 Procedures . 8 7 Network Connection Release Phase . 18 7.1 PrimitiveiParameter and PacketField Relationships 18 7.2 Procedures . 19 Data Transfer Phase - Data Transfer Service . 2 I 8.1 PrimitiveRarameter and PacketFieid Relationships 2 1 8.2 Procedures . 2

10、 1 9 Data Transfer Phase - Receipt Confirmation Service 22 9.1 Primitive and PackedField Relationships . 22 9.2 Procedures . 22 Data Transfer Phase - Expedited Data Transfer Service 22 10.1 PrimitiveParameter and PacketField Relationships 22 10.2 Procedures . 22. 1 1 Data Transfer Phase - Reset Serv

11、ice 23 1 1.1 Primitivehrameter and PacketEield Relationships 23 1 1.2 Procedures . 24 12 Response to Protocol Violations . 25 13.1 Conformance Requirements 26 5.1 5.2 8 1 O 13 Conformance 26 13.2 Optional Features 26 Recommendation X.223 (1 1/93) 1 _. Appendix I I. 1 1.2 Appendix II II. 1 11.2 11.3

12、Appendix III Appendix IV Appendix V - Additional Considerations of CONS Primitives Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

13、. . . Environment for X.25PLP Operation . . - Use ofX.25PLP NPAI . Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . Obtaini

14、ng an SNPA Address . Examples of network Address Encoding - Transit Delay Calculations . . - Mapping of OS1 CONS QOS parameters to parameters in the X. 130 Series Recommendations . - Differences between ITU-T Recommendation X.223 and ISOAEC 8878 Page 27 27 27 28 28 28 29 32 34 35 11 Recommendation X

15、.223 (11/93) STD*ITU-T RECMN X.223-ENGL 1993 L18b2591 0625742 525 Recommendation X.223 (11/93) . 111 SUMMARY Recommendation X.25 is used for many different types of applications. This Recommendation, X.223, shows how to use X.25 for OS1 purposes by specifying a mapping of the appropriate elements of

16、 X.25 to/fiom the OS1 Connection-mode Network Service defined in Recommendation X.213. This revision of X.223 corrects serveral minor errors and achieves complete interworking capability with the corresponding ISO/IEC 8878 Standard. iv Recommendation X.223 (11193) Recommendation X.223 USE OF X.25 TO

17、 PROVIDE THE OS1 CONNECTION-MODE NETWORK SERVICE FOR ITU-T APPLICATIONS*) (Melbourne, 1988; revised at Geneva, 1993) O Introduction This Recommendation defines the method for providing the OS1 Connection-Mode Network Service (CONS) for IT-T Applications through the use of the virtual call services o

18、f the X.25 Packet Layer Protocol (X.25 PLP). Particularly, it specifies a mapping between the elements of the X.25PLP and the primitives of the OS1 CONS specified in CCITT Rec. X.213 I ISO/IEC 8348. Clause 13 contains the requirements for systems claiming conformance to this Recommendation. Appendix

19、 I provides additional considerations on the relationship between the X.25 protocol procedures and the CONS primitives. Appendix II illustrates the use of X.25 Network Protocol Address Information (NPAI), i.e. the Address Field and the Address Extension Facilities. Appendix III illustrates the use o

20、f X.25 transit delay facilities. Appendix IV shows the relationship of the OS1 CONS Quality of Service (QOS) parameters and performance parameters in the X. 130-Series Recommendations. This Recommendation is similar to ISO/IEC 8878; however, the two are currently published as separate documents. A l

21、ist of technical differences is given in Appendix V. The relationship between the X.25PLP and the OS1 CONS is shown in Figure I. This relationship is described only in tenns of the Network Layer entities that provide the CONS. No discussion is given here to describe the actions of a Network Layer en

22、tity that only provides a relay function for a given network connection. TO7201 40-94/d01 FIGURE 1X.223 Relationship of the X.25 Packet Layer Protocol to the OS1 Connection-Mode Network Service This Recommendation and ISO/IEC 8878:1992 were developed coilaboratively and are similar in content. A lis

23、t of technical differences is given in Appendix V. Recommendation X.223 (1 1/93) 1 STD-ITU-T RECMN X-223-ENGL 1773 9Bb2571 Ob25795 239 The OS1 Network Service is defined in terms of a) b) c) the primitive actions and events of the Service; the parameters associated with each primitive action and eve

24、nt, and the form which they take; the interrelationship between, and the valid sequences of, these actions and events. The OS1 Network Service does not speci individual implementations or products nor does it constrain the implementation of entities and interfaces within a computer system. The X.25P

25、LP is defined in terms of a) procedures for Virtual Calls and Permanent Virtual Circuits; b) formats of packets associated with these procedures; c) procedures and formats for optional user facilities and CCITT-Specified DTE facilities. The use of the word “Network” to name the “Network” Layer of th

26、e OS1 Reference Model should be distinguished from the use of the word “network” to denote a communications network as conventionally understood. To facilitate this distinction, the term “subnetwork” is used for a collection of physical equipment, commonly called a “network” (reference CCITT Rec. X.

27、200 I IS0 7498). Subnetworks may be either public or private networks. In the case of public networks, their properties may be determined by separate Recommendations such as CCITT Rec. X.21 for a circuit- switched network or ITU-T Rec. X.25 for a packet-switched network. Thoughout the set of OSI-rel

28、ated Recommendations I Intemational Standards, the term “Service” refers to the abstract capability provided by one layer of the OS1 Reference Model to the layer above it. Thus, the Network Service is a conceptual architectural Service, independent of administrative divisions. NOTE - It is important

29、 to distinguish the specialized use of the term “Service” within the set of OSI-related Recommendations I International Standards from its use elsewhere to describe the provision of a service by an organization (such as the provision of a service, as defined in ITU-T Recommendations, by an Administr

30、ation). 1 Scope The OS1 CONS, as stated above, is defined in terms of a set of primitive actions and events and associated parameters. For a protocol to support this service, there must be a mapping between the abstract primitives and parameters of the CONS and the real elements of the protocol. Thi

31、s Recommendation provides such a mapping for the X.25RLP using Virtual Calls. The X.25RLP is usually regarded as operating between an end system (Le. a “Data Terminal Equipment” in X.25 terminology) and a packet-switched public data subnetwork. However, the X.25/PLP can also be used in other environ

32、ments to provide the OS1 CONS. Examples of such other uses include a) an end system connected to an X.25 packet-switched private data subnetwork; b) c) an end system connected to a local area network; direct connection or circuit-switched connection (including connection across a circuit-switched da

33、ta subnetwork) of two end systems without an intervening packet-switched public data subnetwork; d) an end system connected to an Integrated Services Digital Network. 2 Normative References The following Recommendations and International Standards contain provisions which, through reference in this

34、text, constitute provisions of this Recommendations. 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 are _. 2 Recommendation X.223 (11/93) STD-ITU-T RECMN X.223-ENGL 1793

35、m 48b259L Ob2574b 170 m 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 TSB maintains a list of currently valid IT-T Recommendati

36、ons. 2.1 2.2 2.3 3 3.1 Identical Recommendations I International Standards - ITU-T Recommendation X.21 O (1993) I ISO/IEC 1073 1 : 1993, Informarion Technology - Open Systems Interconnection - Basic Reference Model - Conventions for the definition of OSI services. CCITT Recommendation X.213 (1992) I

37、 ISOffEC 8348:1993, Information Technology - Network Service Definition for Open Systems Interconnection - Paired Recommendations I International Standards Equivalent in Technical Content - CCITT Recommendation X.200 (1988), Rgerence model of Open Systems Interconnection for CCITT applications. IS0

38、7498: 1984, Information processing systems - Open Systems Interconnection - Basic reference model. - Additional References - ITU-T Recommendation X.25 (1993), Interface Between Data Terminal Equipment (DTE) and Data Circuit Terminating Equipment (DCE) for terminals operating in the packet-mode and c

39、onnected to Public Data Networks by dedicated circuit. NOTE - This Recommendation is referred solely with respect to its Packet Layer Protocol description. However, this Recommendation fully specifies the behaviour of the DCE while specieing only a minimum set of requirements for the DTE. Additional

40、 guidance for the design of DTEs is available in ISO/IEC 8208. ITU-T Recommendation X.96 (1 993), Call progress signals in Public Data Networks. ISO/IEC 8208: 1990, Information technology - Data communications - X.25 Packet Layer Protocol for data terminal equipment. - - Definitions Reference Model

41、Definitions The following concepts, developed and defined in the OS1 Reference Model (CCITT Rec. X.200 IS0 7498), are used: a) Network connection; b) Network Layer; c) Network Service; d) Network Service Access Point; e) f) Subnetwork. Network Service Access Point address; 3.2 Service Conventions De

42、finitions The following terms, as they apply to the Network Layer and as defined in the OS1 Service Conventions (ITU-T Rec. X.2 10 I ISOiEC 1073 l), are used: a) Network Service user; b) Network Service provider; c) primitive; Recommendation X.223 (1 1/93) 3. STD-ITU-T RECMN X-223-ENGL I773 18b257L

43、Ob257117 O07 ;3 4 d) request; e) indication; f) response; g) confm. 3.3 Network Service Definitions The following terms, as defined in the Network Service (CCITT Rec. X.213 I ISOhEC 8348), are used: Calling Network Service user; Called Network Service user; Subnetwork Point of Attachment address; Ne

44、twork Protocol Address Information; Initial Domain Part; Authority and Format Identifier; Initial Domain Identifier; Domain Specific Part; 3.4 X.25 Definitions The following concepts, as developed in the X.25 Packet Layer Roto used: a) virtual circuit; b) Virtual Call; e) logical channel; d) Packet

45、Layer; e) Data Terminal Equipment; f) Data Circuit-tetminating Equipment; g) DXE (either a DTE or a DCE). 3.5 X.96 Definitions The following terms, as defined in ITU-T Rec. X.96, are used: Category C call progress signal; Category D call progress signal. a) b) 4 Abbreviations 4.1 Network Service Abb

46、reviations AFI Authority and Format Identifier CONS Connection-Mode Network Service DSP Domain Specific Part ID1 Initial Domain Identifier IDP Initial Domain Part N Network NC Netw ork-connection NL Network Layer 1 (ITU-T Rec. X.25 and ISO/IEC 8208), . r 4 Recommendation X.223 (11/93) NPAI Network P

47、rotocol Address Information NS Network Service NSAP Network Service Access Point OS1 Open Systems Interconnection QOS Qualiy of Service SNPA Subnetwork Point of Attachment 4.2 X.25 Abbreviations AEF Address Extension Facility AF Address Field E-MTCN Basic Minimum throughput Class Negotiation (Facili

48、ty) B-TCN Basic Throughput Class Negotiation (Facility) D-bit Delivery Confirmation bit DCE Data Circuit-terminating Equipment DTE Data Terminal Equipment EDN Expedited Data Negotiation (Facility) EETDN End-to-End Transit Delay Negotiation (Facility) FPF Facility Parameter Field GFI General Format I

49、dentifier LC Logical Channel M-bit More Data bit MBS M-bit Sequence PLP Packet Layer Protocol P(R) Packet receive sequence number P(S) Packet send sequence number Q-bit Qualifier bit TDSAI VC Virtual Call Transit Delay Selection And Indication (Facility) 5 Overview The Network Service (NS) provides for the transparent transfer of data between NS users. It makes invisible to these NS users the way in which supporting communications resources are utilized to achieve this transfer. 5.1 Elements of the X.25 I PLP Used to Support the OS1 CONS The X