1、ITU-T RECMN*X*37 95 48b259L ObObb20 074 INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU DATA NETWORKS AND OPEN SYSTEM COMMUNICATIONS PUBLIC DATA NETWORKS - INTERFACES x.37 (04/95) ENCAPSULATION IN X.25 PACKETS OF VARIOUS PROTOCOLS INCLUDING FRAME RELAY ITU
2、-T Recommendation X.37 (Previously “CCITT Recommendation”) ITU-T RECMN*X.37 95 4862593 0606623 TOO FOREWORD The ITU-T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (ITU). The ITU-T is responsible for studying technical, operating and tar
3、iff questions 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 ITU-T Study Groups which, in their turn, prod
4、uce Recommendations 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). ITU-T Recommendation X.37 was prepared by ITU-T Study Group 7 (1993-1996) and was approved under the WTSC Reso
5、lution No. 1 procedure on the 10th of April 1995. NOTE In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. O ITU 1995 All rights reserved. No part of this publication may be reproduced
6、or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the IT. ITU-T RECflN*X*37 95 4862591 ObObb22 9Y7 Subiect area ITU-X SERIES RECOMMENDATIONS Recommendation Series I DATA NETWORKS AND OPEN SYSTEM COMMUNICATIONS
7、PUBLIC DATA NETWORKS Services and Facilities (February 1994) ORGANIZATION OF X-SERIES RECOMMENDATIONS X. 1-X. 19 Transmission, Signalling and Switching Network Asvects X.50-X.89 X.90-X.149 1 Interfaces I X.20-X.49 I Maintenance Administrative Arrangements OPEN SYSTEMS INTERCONNECTION X. 150-X.179 X.
8、180-X.199 Service Definitions Connection-mode Protocol Specifications I Model and Notation I X. 200-X . 209 I X.210-X.219 X.220-X.229 Connectionless-mode Protocol Specifications PICS Proformas X.230-X.239 X.240-X.259 1 Protocol Identification I X.260-X.269 I Security Protocols Layer Managed Objects
9、X.270-X.279 X.280-X.289 Conformance Testing INTERWORKING BETWEEN NETWORKS I x. 300-x . 349 I General I X.290-X.299 Mobile Data Transmission Systems Management X.350-X.369 - X.370-X.399 I OS1 NETWORKING AND SYSTEM ASPECTS MESSAGE HANDLING SYSTEMS DIRECTORY X.400-X.499 X.500-X.599 I Abstract Syntax No
10、tation One (ASN.1) I X.680-X.699 I Networking Naming, Addressing and Registration I OS1 MANAGEMENT I X.700-X.799 X.600-X.649 X.650-X.679 I SECURITY I X.800-X.849 I OS1 APPLICATIONS Commitment, Concurrency and Recovery Transaction Processing X.850-X.859 X. 860-X. 879 Remote Operations OPEN DISTRIBUTE
11、D PROCESSING X. 880-X. 899 X.900-X.999 _ ITU-T RECMN*X-37 95 4862591 0606623 883 ITU-T RECMNxX.37 95 m 4862573 O606624 7LT m 1 2 3 4 5 6 7 8 9 10 CONTENTS Scope References Terms and definitionsd . Abbreviations . General . 5.1 Encapsulation function location 5.2 Basic features 5.3 Use of X.75 for PD
12、N interconnection 5.4 Protocol stack on the local interface . Call Set-up procedures . 6.1 General 6.2 Call set-up conditions . 6.3 Coding of the call request packet 6.4 6.5 6.6 6.7 Reception of the incoming call packet Coding of the call accepted packet . Reception of the call connected packet . 6.
13、8 Call Set-up collision Call clearing procedures . Negotiation at call Set-up Data Transfer procedure . 8.1 Reception of PDU from the local interface . 8.2 Encapsulation format 8.3 Data transfer on the X.25 virtual call on the network side . 8.4 Flow control Encapsulation of Frame Relay . Procedures
14、 for Frame Relay permanent virtual circuit . 9.1 General Principles . 9.2 9.3 Procedures for switched virtual call 9.4 FR frames transfer procedure . Encapsulation of IP datagrams . 10.1 General Principles . 10.2 Call Set-up procedures 10.3 Call clearing procedures . 10.4 IP datagrams transfer proce
15、dure . 10.5 Flow control Annex A . Protocol Implementation Conformance Statement (PICS) proforma . A.l Instructions for completing the PICS proforma A.2 Identification A.3 Claimed Conformance to standards A.4 Call Set-up procedures AS Call clearing procedures . A.6 Data transfer procedures . A.7 Enc
16、apsulation of Frame Relay A.8 Encapsulation of IP datagrams . A.9 Other information . Recommendation X.37 (04/95) Page 1 1 2 2 3 3 3 5 5 7 7 8 8 10 10 11 11 12 13 13 13 14 14 16 16 16 17 20 20 23 23 23 24 24 25 26 26 28 29 30 31 31 32 36 39 1 ITU-T RECMN*X.37 95 - 4862593 ObObb25 656 Page Annex B .
17、Coding of clearing cause and diagnostic fields generated by an encapsulation function in clear request packet . Appendix I - Application examples 1.1 1.2 X.25 DTE / X.36 DTE interworking for a given encapsulated protocol 1.3 X.25 DTE / X.36 DTE interworking for multi-protocol encapsulation Dynamic n
18、egotiation of the encapsulated protocol . Appendix II - Technical discussion Mode of operation for the multi-PDU transfer . 11.1 11.2 Flow control 11.3 Flow control for the FR case Appendix III - Protocol identification mechanism for data packets when the Q-bit is used 40 41 41 42 43 44 44 44 45 47
19、11 Recommendation X.37 (04/95) ITU-T RECMN*X-37 75 4862591 0606626 592 SUMMARY This Recommendation specifies the X.25 call Set-up and call clearing procedures used by an encapsulation function and the data transfer phase which follows, when using Packet Switched Data Transmission Service to transmit
20、 Protocol Data Units of various protocols. In addition to general procedures, this Recommendation deals with the specific encapsulation in X.25 packets of Frame Relay frames and IP datagrams. . Recommendation X.37 (04/95) 111 ITU-T RECMN*X.37 95 m 4862593 Ob06627 qZ.9 m ?- -7 ITU-T RECMN*X=37 95 m 4
21、8b2591 ObObb2 3b5 m Recommendation X.37 ENCAPSULATION IN X.25 PACKETS OF VARIOUS PROTOCOLS INCLUDING FRAME RELAY (Geneva, 1995) 1 Scope This Recommendation defines the use of Packet Switched Data Transmission Service to transmit Protocol Data Units of various protocols including: - - FrameRelay. pro
22、tocols used in Local Area Network; The aim of this Recommendation is to favour: - - inter-operability between equipments (e.g. routers); interworking between DTEs which are connected to PDNs but do not use the same data transmission services (e.g. Frame Relay and Packet Switched data transmission se
23、rvice); network optimisation, both on user and operator levels, by increasing the use of existing and forthcoming infrastructures ; - - - promotion of Packet Switched Data Transmission Services; promotion of X.75 use for PDN interconnection; This Recommendation makes use of the protocol identifiers
24、defined in ISO/IEC TR 9577. Appendix I provides application examples which illustrate some of the preceding items. 2 References The following Recommendations, and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of p
25、ublication, the editions indicated were valid. All Recommendations and other references are subject to revision: all users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A li
26、st of the currently valid ITU-T Recommendations is regularly published. - ITU-T Recommendation X.25 (1993), lnteqace between 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 circu
27、its. ITU-T Recommendation X.29 (1993), Procedures for the exchange of control information and user data between a Packet Assembly/Disassembly (PAD) facility and a packet mode DTE or another PAD. - - ITU-T Recommendation X.36 (1993, Inteqace between Data Terminal Equipment (DTE) and Data Circuit- ter
28、minating Equipment (DCE) for public data networks providing frame relay data transmission service by dedicated circuit. - CCITT Recommendation X.39 (1992). Procedures for the exchange of control information and user data between a Facsimile Packet Assembly/Disassembly (FPAD) faciLi and a packet mode
29、 Data Terminal Equipment (DTE) or another FPAD. - ITU-T Recommendation X.75 (1993), Packet switched signalling system between public networks providing data transmission services. - ITU-T Recommendation X.76 (1993, Network-to-network inteflace between public data networks providing the frame relay d
30、ata transmission service. Recommendation X.37 (W95) 1 ITU-T RECMNtX.37 95 4862591 0bObb27 2Tl - - IT-T Recommendation X.224 ( 1993), Protocol for providing the OS1 connection-mode transport service. ISOIIEC 8073: 1992, Information technology - Telecornmunications and information exchange between sys
31、tems - Open Systems Interconnection - Protocol for providing the connection mode network service. ITU-T Recommendation X.622 (1994) I ISO/IEC 8473-3 .I), Information technology - Potoco1 for providing the connectionless-mode Network service: Povision of the underlying service by an X.25 subnetwork.
32、ISOAEC TR 9577 (second edition ). Infomation technology - Telecommunications and information exchange between systems - Protocol identification in the network layer. - - 3 Terms and definitions For the purpose of this Recommendation, the following definitions apply: 3.1 encapsulation function: A fun
33、ction which may reside inside an X.25 DTE or inside a Packet Switched Public Data Network. When it receives a PDU of a given protocol from the user equipment, it transmits this PDU within a complete packet sequence on an X.25 virtual call. When it receives a PDU of a given protocol within a complete
34、 packet sequence, it retrieves this PDU and transmits it towards the user equipment. It may also provide interworking function between the local interface protocol and Recommendation X.25. 3.2 an encapsulation function and a user equipment, before encapsulation and after de-encapsulation in X.25 pac
35、kets. 3.3 X.25 packets. load interface: The interface which is used to transfer Protocol Data Units of one protocol (or more) between PDU: The abbreviation PDU refers to Protocol Data Units of the protocol(s) which is(are) encapsulated in 4 Abbreviations For the purpose of this Recommendation the fo
36、llowing abbreviations are used: BECN CLNP C/R CRC DCE DE DLCI DNIC DTE IP FECN FR LAN LCN MTU PICS PDU Backward Explicit Congestion Notification Connectionless Network Protocol CommandResponse Cyclic Redundancy Code Data Circuit-terminating Equipment Discard Eligibility Data Link Connection Identifi
37、er Data Network Identification Code Data Terminal Equipment Internet Protocol Forward Explicit Congestion Notification Frame Relay Local Area Network Logical Channel Number Maximum Transmission Unit Protocol Implementation Conformance Statement Protocol Data Unit To be published. 2 Recommendation X.
38、37 (04/95) ITU-T RECMN*X-37 95 4862591 O606630 T13 PSPDN Packet Switched Public Data Network PVC Permanent Virtual Circuit (for Frame Relay) RFC Request for Comment SNAP Single Network Access Protocol 5 General This Recommendation defines the X.25 call set-up and call clearing procedures used by an
39、encapsulation function, and the data transfer phase which follows. These procedures are categorised as follows: - - procedures which are independent of the protocol being encapsulated: see clauses 6.7 and 8; procedures which are dependent on the protocol being encapsulated: see clauses 9 and 10. Whe
40、n referring to Recommendation X.25 in this Recommendation, a reference is made to all uses of the packet layer which includes cases described in Recommendations X.31, X.32, etc. When referring to Recommendation X.36, a reference is made to all uses of Frame Relay protocol which includes cases descri
41、bed in ISDN Recommendations (See Q- and I-Series Recommendations). When dealing with encapsulation of various protocols, a given encapsulated protocol is identified by an identifier defined in ISOAEC TR 9577 (second edition). In relation to X.25, relevant material is given on the use of the followin
42、g ISO/IEC TR 9577 (second edition) defined protocol identifiers: - - - - - NOTE -At the time of publication, code points hexadecimal AO and A8 are agreed to be included in the third version of multi-protocol encapsulation (hexadecimal 00), see 5.2.1.2,6.3.4.1 and 8.2.2; IEEE SNAP convention (hexadec
43、imal 80), see 6.3.4.1; identification of the protocol through other means (hexadecimal AO) see 6.3.4.1; Frame Relay according to X.37 (hexadecimal Ag) see clause 9; Internet Protocol (hexadecimal CC) see clause 10. ISODEC TR 9577 and in forthcoming equivalent ITU-T Recommendations. In addition to IS
44、O/IEC TR 9577 aspects for X.25, Appendix III provides additional protocol identification mechanisms for data packets when the X.25 Q-bit is used. In addition to this Recommendation, relevant material can be found in: - - - Recommendation X.622 i ISO/IEC 8473-3, encapsulation of CLNP; Recommendation
45、X.39, encapsulation of data from a Fax PAD; Recommendation X.29, encapsulation of data from a start stop PAD. To claim its compliance to this Recommendation, a network or an encapsulation function must follow the requirements defined in Annex A. 5.1 Encapsulation function location As shown in Figure
46、 1, the encapsulation function may reside inside an X.25 DTE or inside the PSPDN. 5.2 Basic features This subclause describes the basic features regarding the way protocols are encapsulated and transferred over an X.25 virtual call between two encapsulation functions. Recommendation X.37 (04/95) 3 I
47、TU-T RECMN*X.37 95 = 48b2591 DbObb31 95T = A A LAN protocols Frame Relay Other protocols / f -. Other protocols f A LAN protocols l v A l f Frame Relay Encapsdation PSPDN Function f Other protocols I f f T71983094/a)l NOTES 1 The protocols indicated here on the local interface are only examples. 2 T
48、he above depiction may imply that a system containing an encapsulation function does not originate any encapsulated protocols. This may not be the case as shown in Appendix I. FIGURE 1K.37 Possible locations a the encapsulation function 5.2.1 Encapsulation methods The encapsulation method is negotia
49、ted at call Set-up between the two encapsulation functions. 5.2.1.1 Mono-protocol encapsulation The mono-protocol method allows to encapsulate PDUs of a single protocol over an X.25 virtual call. Both encapsulation functions identify the encapsulated protocol at call Set-up in the call user data field of the call Set-up packets using protocol identifiers which are defined in ISO/IEC TR 9577 (second edition). 5.2.1.2 Multi-protocol encapsulation The multi-protocol method allows to encapsulate PDUs of several protocols over a single X.25 virtual call. 4 Recommenda
