1、 STD*ITU-T RECMN X*ZbO-ENGL 177b Li862591 Ob2qb55 305 INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUN CATION STANDARDIZATION SECTOR OF ITU X.260 (1 0/96) SERIES X: DATA NETWORKS AND OPEN SYSTEM COM M U N I CAT I ON Open System Interconnection - Protocol Identification Information technology -
2、 Framework for protocol identification and encapsulation ITU-T Recommendation X.260 (Previously “CCITT Recommendation”) STD-ITU-T RECMN X-2bO-ENGL 177b D LiBb257L Ob2Lib5b 2LiL D ITU-T X-SERIES RECOMMENDATIONS DATA NETWORKS AND OPEN SYSTEM COMMUNICATION -_ _ UBLIC DATA NETWORKS X. 1-X. 199 Services
3、and facilities X. 1-X.19 Interfaces X.20-X.49 Transmission, signalling and switching X.50-X.89 Network aspects X.90-X.149 Maintenance X.150-X. 179 Administrative arrangements X.180-X. 199 Model and notation X.200-X.209 Service defmitions X.210-X.219 Connection-mode protocol specifications X.220-X.22
4、9 Connectionless-mode protocol specification X.230-X.239 PICS proformas X.240-X.259 * -_ - - Prot X.260-X.269 Security Protocols X.270-X.279 Layer Managed Objects Conformance testing General NTERWORKING BETWEEN NETWORKS X.280-X.289 X.290-X.299 X.300-X.399 X.300-X.349 Satellite data transmission syst
5、ems X.350-X.399 MESSAGE HANDLING SYSTEMS DIRECTORY OS1 NETWORKING AND SYSTEM ASPECTS Networking X.400-X.499 X.500-X.599 X.600-X.699 X.600-X.629 Efficiency X.630-X.649 Naming, Addressing and Registration X.650-X.679 Abstract Syntax Notation One (ASN. 1) X.680-X.699 OS1 MANAGEMENT Systems Management f
6、ramework and architecture X.700-X.799 X.700-X.709 Management Communication Service and Protocol X.7 IO-X.719 Structure of Management Information X.720-X.729 Management functions SECURITY OS1 APPLICATIONS Commitment, Concurrency and Recovery Transaction processing Remote operations X.730-X.799 X.800-
7、X.849 X.850-X.899 X.850-X.859 X.860-X.879 X. 8 8 O-X. 899 OPEN DISTRIBUTED PROCESSING X.900-X.999 For further details, please refer to ITU-T List of Recommendations. STD-ITU-T RECMN X-2bO-ENGL L97b D YBb259L Ob24b57 188 ISOAEC 14765 : 1997 (E) FOREWORD IT (International Telecommunication Union) is t
8、he United Nations Specialized Agency in the field of telecommunications. The IT Telecommunication Standardization Sector (ITiJ-T) is a permanent organ of the XTU. Some 179 member countries, 84 telecom operating entities, 145 scientific and industrial organizations and 38 international organizations
9、participate in IT-T which is the body which sets world telecommunications standards (Recommendations). 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 Con
10、ference (WTSC), which meets every four years, approves Recommendations submitted to it and establishes 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 IE
11、C. The text of ITU-T Recommendation X.260 was approved on 5th of October 1996. The identical text is also published as ISOAEC International Standard 14765. NOTE In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a r
12、ecognized operating agency. O ITU 1997 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 and microfilm, without permission in writing from the ITU. ITU-T Rec. X.260 (1996 E) 1 ISOiEC 14765 : 19
13、97 (E) CONTENTS 1 2 3 4 5 6 7 Scope Normative references . 2.1 Identical Recommendations I International Standards 2.2 Additional references Abbreviations . Definitions and concepts Basic Reference Model concepts Additional definitions and concepts 4.1 4.2 Overview 5.1 General 5.2 Interworking and e
14、ncapsulation Principles of protocol identification . 6.1 Need for protocol identification 6.2 Protocol identifier registries and values 6.3 Protocol identification methods 6.4 Protocol identifiers Principles of protocol encapsulation 7.2 Protocol encapsulation methods 7.1 Encapsulation function 7.3
15、Relationships among EFs, EdPs, and EgPs . Annex A . Current Recommendations I International Standards supporting PIE principles Annex B . Examples of protocol identification and encapsulation methods 11 ITU-T Rec . X.260 (1996 E) Page 1 1 1 2 2 2 2 2 3 3 3 5 5 5 5 6 7 1 9 9 15 17 STD-ITU-T RECMN X.2
16、bO-ENGL Ib W Li8b25L b2Lib57 T5O m ISOfiEC 14765 : 1997 (E) Summary This Recommendation I International Standard provides a framework for explicit identification and encapsulation of Network Layer protocols. . ITU-T Rec. X.260 (1996 E) 111 P Lid ISOAEC 14765 : 1997 (E) INTERNATIONAL STANDARD ITU-T R
17、ECOMMENDATION INFORMATION TECHNOLOGY - FRAMEWORK FOR PROTOCOL IDENTIFICATION AND ENCAPSULATION 1 Scope In a layered approach to protocol architecture, protocols have a relationship to one another such that a protocol at layer (n) uses the services of the layer below it - the (n- 1) services - which,
18、 in turn, are provided by a layer (n - 1) protocol. One of the services used by a layer (n) protocol is the encapsulation of its (n) Protocol Data Units (PDUs) in a way which is transparent to it. Such encapsulation is realized by the caniage of the (n) PDUs as user data in an (n - 1) Service Data U
19、nit (SDU). In a limited case, the operation of a particular protocol at layer (n - 1) implies the operation, above layer (n - i), of a single layer (n) protocol or single set of related (n) / (n + 1). . . protocols. However, in a more general case, there may be more than one protocol (or set of rela
20、ted protocols starting) at layer (n) that can operate above layer (n - 1) in a given environment. In such cases, there is a need for explicit identification of the protocol (or set of protocols starting) at layer (n). There also may be a need to manipulate the (n - i) protocol (i.e. the encapsuhting
21、 protocol) in certain ways specific to the layer (n) protocol (i.e. the encapsulated protocol). Such manipulations form the basis of a set of procedures that must be specified for the layer (n) protocol. The above observations regarding protocol identification and encapsulation are also applicable i
22、n cases where an (n) layer is further divided into sublayers. Cases in which an (n) protocol operates for the purpose of establishing a parallel universe of protocols (regardless of the layered structure of that universe) also give rise to a need for the (n) protocol to be able to identify the proto
23、col(s) in the parallel universe. In these cases, however, there is no encapsulatingencapsulated relationship between the (n) protocol and the parallel universe set of protocols. The above principles lead to a need to establish a framework for protocol identification and encapsulation. These principl
24、es apply to the relationship between two protocols (recognizing that one of them may be a set of related protocols) and can be applied recursively. This Recommendation I International Standard provides a framework for explicit protocol identification and for protocol encapsulation. Implicit protocol
25、 identification (see 4.2) is beyond the scope of this Recommendation 1 International Standard. 2 Normative references The following Recommendations and International Standards contain provisions which, through reference in Uiis text, constitute provisions of this Recommendation I International Stand
26、ard. At the time of publication, the editions indicated were valid. All Recommendations and Intemational Standards are subject to revision, and parties to agreements based on this Recommendation I Intemational Standard are encouraged to investigate the possibility of applying the most recent edition
27、 of the Recommendations and International 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 ITU-T Recommendations. 2.1 Identical Recommendations I I
28、nternational Standards - IT-T Recommendation X.200 (1994) I ISOAEC 7498-1:1994, Information technology - Open Systems Interconnection - Basic Reference Model: The Basic Model. ITU-T Recommendation X.263 (1995) I ISOAEC TR 9577:1996, Information technology - Protocol identification in the network lay
29、er. - ITU-T Rec. X.260 (1996 E) 1 STD-ITU-T RECMN X-2bO-ENGL Lb m 48b25L Ob2Libb2 545 ISOAEC 14765 : 1997 (E) 2.2 Additional references - ITU-T Recommendation X.37 (1995), Encapsulation in X.25 packets of various protocols including fiame relay. ISOAEC 135 15 1, Information technology - Telecommunic
30、ations and information exchange between systems - Generic Multiprotocol Encapsulation (GA): Application to fiame relay and ATM. - 3 Abbreviations EdP Encapsulated Protocol EF Encapsulation Function EgP Encapsulating Protocol EPIF Encapsulated Protocol Information Field IdP Identified Protocol(s) IgP
31、 Identifjing Protocol IPI Initial Protocol Identifier PCI Protocol Control Information PDU Protocol Data Unit PEM Protocol Encapsulation Method PId Protocol Identification PIE Protocol Identification and Encapsulation PIM Protocol Identification Method SDU Service Data Unit SPI Subsequent Protocol I
32、dentifier 4 Definitions and concepts 4.1 Basic Reference Model concepts The following concepts from ITU-T Rec. X.200 I ISOIEC 7498-1 are used here: concatenation; layer; protocol; Protocol Control Information (PCI); Protocol Data Unit (PDU); protocol identification; protocol identifier; segmentation
33、reassembly ; Service Data Unit (SDU); sublayer. 4.2 Additional definitions and concepts The definitions and concepts below apply to this Recommen-ation 1 Internatione Stan-ad. 4.2.1 is used to identi a protocol, a set of related protocols, or a family of protocols. explicit protocol identification m
34、ethod: An explicit PiM is one in which Protocol Control Information (PCI) ) Presently at the stage of draft. 2 ITU-T Rec. X.260 (1996 E) STD-ITU-T RECMN X-2bO-ENGL L77b W 48b257L Ob24bb3 Li81 ISOAEC 14765 : 1997 (E) 4.2.2 implicit protocol identification method An implicit PIM is one in which there
35、is no PCI used to identie a protocol. Identification occurs through mechanisms such as coupling in a Recomrhendation or International Standard of an IgF with an IdP e.g. stating that a specific (n) protocol is used above an (n - 1) protocol; association of a physical port of a system with one or a s
36、et of related protocols; or association at provisioning of a “permanent” connection. 4.2.3 set of alternative protocols: Given protocols protl, protz, etc., then proti, protz, etc. all operate at the same layer or sublayer. 4.2.4 set of related protocols: Given protocols protl, protz, etc., then pro
37、tl operates at layer (n), protz operates at layer (n + i), etc. (where the layers may also be hierarchical sublayers). 4.2.5 family of protocols: Given a set of alternative protocols protl, prot2, etc., a single identifier is used to identify the set of alternative protocols as a whole, thereby requ
38、iring additional methods to identify one member of the family. 5 Overview 5.1 General As discussed above, there may exist a relationship between protocols that gives rise to a need for one protocol - the Identieing Protocol (i) - to identi one of a set of altemative protocols, a set of related proto
39、cols, or a family of protocols - the Identified Protocol(s) (IdP). As a result of the identification process, a second relationship may be created between an Encapsulating Protocol (E) and an Encapsulated Protocol(s) (EdP). In some cases, the IgP and the EgP may be the same protocol. It is usually t
40、he case that an IdP and an EdP are the same. To provide a basis for developing the necessary relationships among specific protocols, a framework is developed here to set out the principles of Protocol Identification and Encapsulation (PIE). These principles recognize the following aspects of PIE: de
41、velopment of Protocol Identification Methods (PIMs) for identifying an IdP (e.g. the location in the IgP - such as in a particular field: header, trailer, etc. - used to identi the IdP); for each PIM, registration of values of IdPs; requirement on an IgP to specify the PIM it uses to identify IdPs a
42、nd any further IgP-specific procedures involving the PIM; development of Protocol Encapsulation Methods (PEMs) for use by EgPs; and specification of operations (e.g. limitations, specific manipulations, etc.) of an EgP for a specific EdP. a) b) c) d) e) The above aspects are depicted in Figure 1. An
43、nex A presents the current status of Recommendations and International Standards in alignment with the framework depicted in Figure 1. 5.2 Interworking and encapsulation Interworking and encapsulation of protocols are two closely related concepts. For the purposes of this Recommen- dation I Internat
44、ional Standard, the following distinctions are made. Interworking occurs between two or more protocols at the same layer (or sublayer). It is concerned only with the semantic aspects of the (n) layer protocols. In particular, interworking is concerned with the transformation between the semantics of
45、 an (n) layer protocol used on one interface and the semantics of other (n) layer protocols used on the other interfaces. The protocols used on the different interfaces may or may not be the same. The transformation between protocols may result in the preservation of the semantic content of all prot
46、ocols on an end-to-end basis. The transformation only applies to the set of abstract capabilities (or sewice) which the protocols have in common. On the other hand, the transformation may result in a loss of semantic content when crossing interfaces. Encapsulation (or tunneling as it is sometimes ca
47、lled) occurs when a given protocols PDU (or set of PDUs if the protocol provides segmentationreassembly capabilities) is used to cany the PDUs of another protocol that is, the user data parameter of an (n - 1) SDU is used to carry the (n) PDU(s). In the general case, no other relationships, such as
48、a strict layering relationship, need exist between the two protocols (e.g. allowing for sublayering or for a given protocol to be encapsulated by protocols with different layer classifications). Encapsulation completely preserves the semantics of the EdP. From the perspective of this Recommendation
49、I International Standard, port access, as a method for interworking as defined in Recommendation X.300, is viewed as a method of encapsulation. ITU-T Rec. X.260 (1996 E) 3 STD-ITU-T RECMN X-2bO-ENGL L99b m i8b259L ObZYbbY 318 m Protocol identification methods ISODEC 14765 : 1997 (E) Protocol encapsulation methods General concepts -_-_-_-_-.- 4 Application of general concepts Framework for Protocol Identification and Encapsulation Encapsulating protocol:
