Information technology - Open Systems Interconnection - Transport service definition (ISO/IEC 8072:1994)

Migrated from Progress Sheet (TC Comment) (2000-07-10): Delayed in PTE.

Technologies de l'information - Interconnexion de systemes ouverts (OSI) - Définition du service de transport (ISO/IEC 8072:1994)

Information technology - Open Systems Interconnection - Transport service definition (ISO/IEC 8072:1994)

General Information

Status
Withdrawn
Publication Date
31-Dec-1997
Withdrawal Date
30-Sep-2003
Technical Committee
Current Stage
9900 - Withdrawal (Adopted Project)
Start Date
01-Oct-2003
Due Date
01-Oct-2003
Completion Date
01-Oct-2003

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EN ISO/IEC 8072:1998
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2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Information technology - Open Systems Interconnection - Transport service definition (ISO/IEC 8072:1994)Technologies de l'information - Interconnexion de systemes ouverts (OSI) - Définition du service de transport (ISO/IEC 8072:1994)Information technology - Open Systems Interconnection - Transport service definition (ISO/IEC 8072:1994)35.100.40Transportni slojTransport layerICS:Ta slovenski standard je istoveten z:EN ISO/IEC 8072:1995SIST EN ISO/IEC 8072:1998en01-januar-1998SIST EN ISO/IEC 8072:1998SLOVENSKI
STANDARD



SIST EN ISO/IEC 8072:1998



SIST EN ISO/IEC 8072:1998



SIST EN ISO/IEC 8072:1998



1 N T ER NAT I O NA L STANDARD ISO/IEC 8072 Second edition 1994-08-01 Information technology - Open Systems Interconnection - Transport service definition Technologies de l'information - Interconnexion de syst&mes ouverts (OS4 - Définition du service de transport Reference number ISO/I EC 8072: 1994(E) SIST EN ISO/IEC 8072:1998



ISO/iEC 8072: 1994(E) CONTENTS SECTION 1 . GENERAL . 1 Scope . 2 Normative references . 3 Definitions . 4 Abbreviations . 5 Conventions . 6 Overview and general characteristics . 7 SECTION 2 - DEFINITION OF THE CONNECTION-MODE SERVICE . 8 9 10 11 12 Classes and types of Transport Service . Features of the connection-mode Transport Service . Model of the connection-mode Transport Service . Quality of connection-mode Transport Service . Sequence of Transport Service primitives . Transport Connection establishment phase . 13 Data transfer phase . Transport Connection release phase . Features of the connectionless-mode Transport Service . Model of the connectionless-mode Transport Service . Quality of connectionless-mode Transport Service . Sequence of connectionless-mode primitives at one TSAP . 14 SECTION 3 - DEFINITION OF THE CONNECTIONLESS-MODE SERVICE . 15 16 17 18 19 Data transfer . Page 1 1 1 1 3 3 3 4 4 4 4 6 10 13 16 18 21 21 21 22 23 24 a a O ISO/IEC 1994 All rights reserved . Unless otherwise specified. 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 publisher . Printed in Switzerland ISO/IEC Copyright Office Case postale 56 CH-121 1 Genève 20 Switzerland 11 SIST EN ISO/IEC 8072:1998



0 ISO/IEC ISODEC 8072:1994(E) Foreword IS0 (the International Organization for Standardization) and IEC (the Inter- national Electrotechnical Commission) form the specialized system for worldwide standardization. National bodies that are members of IS0 or IEC participate in the development of International Standards through technical committees established by the respective organization to deal with particular fields of technical activity. IS0 and IEC technical committees collaborate in fields of mutual interest. Other international organizations, governmental and non-governmental, in liaison with IS0 and IEC, also take part in the work. In the field of information technology, IS0 and IEC have established a joint technical committee, ISOBEC JTC 1. Draft International Standards adopted by the joint technical committee are circulated to national bodies for voting. Publication as an International Standard requires approval by at least 75 % of the national bodies casting a vote. International Standard ISOBEC 8072 was prepared by Joint Technical Committee ISOAEC JTC 1, Information technology, Subcommittee SC 6, Telecommunica- tions and information exchange between systems, in collaboration with ITU-T. The identical text is published as ITU-T Recommendation X.214. This second edition cancels and replaces the first edition (IS0 8072: 1986), which has been technically revised and consolidates Addendum 1 : 1986 and Technical Corrigendum 1 : 199 1. SIST EN ISO/IEC 8072:1998



ISOnEC 8072: 1994(E) O ISO/IEC Introduction This Recommendation I International Standard is one of a set of Recommendations I International Standards produced to facilitate the interconnection of computer systems. It is related to other Recommendations I International Standards in the set as defined by the Reference Model of Open Systems Interconnection (OSI). The OS1 Reference Model (CCITT Rec. X.200 I IS0 7498) subdivides the area of standardization for interconnection into a series of layers of specification, each of manageable size. This Recommendation I International Standard defines the Service provided by the Transport Layer to the Session Layer at the boundary between the Transport and Session Layers of the Reference Model. It provides for the designers of Session Protocols a definition of the Transport Service existing to support the Session Protocol and for designers of Transport Protocols a definition of the services to be made available through the action of the Transport Protocol over the underlying service. This relationship is illustrated in Figure Intro. 1. r- Session Protocol Session layer Transport Protocol layer user 1 Transport service A provider I service Figure Intro.1- Relationship of the Transport Service to OS1 transport and Session Protocols Throughout the set of OS1 Recommendations I International 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 Transport Service defined in this Recommendation I International Standard is a conceptual architectural Service, independent of administrative divisions. NOTE - It is important to distinguish the specialized use of the term “Service” within the set of OS1 Recommendations I International Standards from its use elsewhere to describe the provision of a service by an organisation (such as the provision of a service, as defined in other Recommendations, by an Administration). iv SIST EN ISO/IEC 8072:1998



ISO/IEC 8072 : 1994(E) INFORMATION TECHNOLOGY - OPEN SYSTEMS INTERCONNECTION - TRANSPORT SERVICE DEFINITION INTERNATIONAL STANDARD ITU-T RECOMMENDATION SECTION 1 - GENERAL 1 Scope This Recommendation I International Standard defines in an abstract way the externally visible service provided by the OS1 Transport Layer in terms of a) b) c) the primitive actions and events of the service; the parameter data associated with each primitive action and event; the relationship between, and the valid sequences of, these actions and events. The service defined in this Recommendation I International Standard is that which is provided by all OS1 Transport Protocols (in conjunction with the Network Service) and which may be used by any OS1 Session Protocol. This Recommendation I International Standard does not specify individual implementations or products, nor does it constrain the implementation of entities and interfaces within a system. Conformance of equipment to this Recommendation I International Standard is achieved by conformance to the protocols specified to fulfil the Transport Service defined in this Recommendation I International Standard. 2 Normative references The following Recommendations and International Standards contain provisions which, through reference in this text, constitute provisions of this Recommendation I International Standard. At the time of publication, the editions indicated were valid. Ail Recommendations and Standards are subject to revision and parties to agreements based on this 0 Recommendation I International Standard are encouraged to investigate the possibility of applying the most recent edition 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 International Standards - ITU-T Recommendation X.210 (1993) I ISO/IEC 10731:1993, Information technology - Open Systems Interconnection - Basic Reference Model - Conventions for the definition of OSI services. 2.2 Paired Recommendations I International Standards equivalent in technical contents - CCITT Recommendation X.200 (1988), Reference model for Open Systems Interconnection for CCIïT applications. IS0 7498: 1984, Information processing systems - Open Systems Interconnection - Basic Reference Model. 3 Definitions For the purpose of this Recommendation I International Standard, the following definitions apply. ITU-T Rec. X.214 (1993 E) 1 SIST EN ISO/IEC 8072:1998



ISO/IEC 8072 : 1994(E) 3.1 Reference Model definitions This Service Definition is based on the concepts developed in the OS1 Reference Model (CCITT Rec. X.200 I IS0 7498), and makes use of the following terms defined in it: a) expedited transport-service-data-unit; b) transport-connection; c) transport-connection endpoint; d) Transport Layer; e) Transport Service; f) transport-service-access-point; g) transport-service-access-point address; h) transport-service-data-unit; i) Network Layer; j) Network Service; k) network-connection; 1) interface flow control. 3.2 Service (Definition) conventions O This Service Definition also makes use of the following terms defined in ITU-T Rec. X.210 I ISO/IEC 10731, as they apply to the Transport L,ayer: a) service-user; b) service-provider; c) primitive; d) request; e) indication; f) response; g) confirm. 3.3 Transport Service Definitions I For the purpose of this Service Definition, the following definitions also apply. 3.3.1 of data, which provides explicit identification of a set of transport data transmissions and agreement concerning the 0 services to be provided for the set. transport connection: An association established by a Transport Layer between two TS users for the transfer I NOTE - This definition clarifies that given in CCIïT Rec. X.200 I IS0 7498. 3.3.2 calling TS user: A Transport Service user that initiates a transport connection establishment request. 3.3.3 called TS user: A Transport Service user with whom a calling TS user wishes to establish a transport connection. NOTE - Calling TS users and called TS users are defined with respect to a single connection. A Transport Service user can be both a calling and a called TS user simultaneously. 3.3.4 transport connection-mode data transmission: The transfer of a TSDU from a source TSAP to a destination TSAP within the context of a TC that has previously been established. 3.3.5 transport connectionless-mode data transmission: The transmission of a TSDU from a source TSAP to a destination TSAP outside the context of a TC and without any requirement to maintain any logical relationship among multiple TSDUs. 3.3.6 sending TS user: A Transport Service user that acts as a source of data during the data transfer phase of a transport-connection, or during a particular instance of transport connectionless-mode data transmission. 3.3.7 receiving TS user: A Transport Service user that acts as a sink of data during the data transfer phase of a transport-connection, or during a particular instance of transport connectionless-mode data transmission. NOTE - A Transport Service user can be both a sending and a receiving TS user simultaneously. I 2 ITU-T Rec. X.214 (1993 E) I SIST EN ISO/IEC 8072:1998



ISOnEC 8072 : 1994(E) 4 Abbreviations TS Transport Service TC Transport-connection TSAP Transport-service-access-point TSDU Transport-service-data-unit QOS Quality of Service 5 Conventions 5.1 General conventions This Service Definition uses the descriptive conventions given in ITU-T Rec. X.210 I ISO/IEC 10731. 5.2 Parameters The available parameters for each group of primitives are set out in tables in clauses 12 to 14 and 19. Each “X’ in the tables indicates that the primitive labelling the column in which it fails may carry the parameter labelling the row in Some entries are further qualified by items in brackets. These may be: indications that the parameter is optional in some way: (U) indicates that the inclusion of the parameter is a choice made by the user; 0 which it falls. a) b) a parameter specific constraints: (=) indicating that the value supplied in an indication or confirm primitive is always identical to that supplied in the previous request or response primitive issued at the peer service access point. 6 Overview and general characteristics The Transport Service provides transparent transfer of data between TS users. It relieves these TS users from any concern about the detailed way in which supporting communications media are utilized to achieve this transfer. The Transport Service provides for the following: b) Quality of Service selection The Transport Layer is required to optimize the use of available communications resources to provide the Quality of Service required by communicating TS users at minimum cost. Quality of Service is specified through the selection of values for Quality of Service parameters representing characteristics such as throughput, transit delay, residual error rate and failure probability. Independence of underlying communications resources The Transport Service hides from TS users the difference in the Quality of Service provided by the Network Service. This difference in Quality of Service arises from the use of a variety of communications media by the Network Layer to provide the Network Service. End-to-end significance The Transport Service provides for the transfer of data between two TS users in end systems. Transparency of transferred information The Transport Service provides for the transparent transfer of octet-aligned TS user-data and/or control information. It does neither restrict the content, format, or coding of the information, nor does it ever need to interpret its structure or meaning. TS user addressing The Transport Service utilizes a system of addressing which is mapped into the addressing scheme of the supporting Network Service. Transport-addresses can be used by TS users to refer unambiguously to TSAPs. ITU-T Rec. X.214 (1993 E) 3 SIST EN ISO/IEC 8072:1998



ISOLCEC 8072 : 1994(E) 7 There are two types of Transport Service: Classes and types of Transport Service a) b) a connection-mode service (defined in clauses 8 to 14); and a connectionless-mode service (defined in clauses 15 to 19). When referring to this Service Definition, a user or provider of TS shall state which type@) of service it expects to use or provide. There are no distinct classes of Transport Service defined. SECTION 2 - DEFINITION OF THE CONNECTION-MODE SERVICE 8 Features of the connection-mode Transport Service The connection-mode Transport Service offers the following features to a TS user: a) b) The means to establish a TC with another TS user for the purpose of exchanging TSDUs. More than one TC may exist between the same pair of TS users. Associated with each TC at its time of establishment, the opportunity to request, negotiate, and have agreed by the TS provider a certain Quality of Service as specified by means of Quality of Service parameters. The means of transferring TSDUs on a TC. The transfer of TSDUs which consist of an integral number of octets is transparent, in that the boundaries of TSDUs and the contents of TSDUs are preserved unchanged by the TS provider and there are no constraints on the TSDU content imposed by the TS provider. The means by which the receiving TS user may control the rate at which the sending TS user may send octets of data. The means of transferring separate expedited TSDUs when agreed to by both TS users. Expedited TSDUs transfer is subject to a different flow control from normal data across the TSAP. The unconditional and therefore possible destructive release of a TC. c) d) e) f) 9 9.1 General This Service Definition uses the abstract model for a layer service defined in ITU-T Rec. X.210 I ISO/IEC 10731. The model defines the interactions between the TS users and the TS provider which take place at the two TSAPs. Information is passed between a TS user and the TS provider by service primitives, which may convey parameters. The primitives are abstract representations of TSAP interactions. They are solely descriptive and do not represent a specification for implementation. Model of the connection-mode Transport Service 9.2 The operation of a TC is modelled in an abstract way by a pair of queues linking the two TSAPs. There is one queue for each direction of information flow (see Figure 1). Each TC is modelled by a separate pair of queues. The queue model is used to introduce the flow control feature. The ability of a TS user to add objects to a queue will be determined by the behaviour of the TS user removing objects from that queue and the state of the queue. Objects are entered and removed from the queue as a result of interactions at the two TSAF's. The pair of queues is considered to be available for each potential TC. Model of a Transport Connection 4 ITU-T Rec. X.214 (1993 E) SIST EN ISO/IEC 8072:1998



ISOfiEC 8072 : 1994(E) TS TS user A user B A A lr lf TS Provider Queue from A to B Queue from B to A Figure 1 - Abstract model of a Transport Connection The objects which may be placed in a queue by a TS user (see clauses 12, 13 and 14) are: a) connect objects (each representing all parameters contained in a T-CONNECT request or T-CONNECT response primitive); b) octets of normal data; c) e indications of end-of-TSDU (completion of a T-DATA primitive); d) e) NOTES 1 2 expedited TSDUs (representing all parameters of a T-EXPEDITED-DATA primitive); disconnect objects (each representing all parameters contained in a T-DISCONNECT primitive). Normal and expedited TSDU transfer will result in different objects being entered into the queue. The description of flow control requires a less abstract description than that used for describing sequences of primitives in clauses 11 to 14. Each TSDU associated with a T-DATA primitive is here subdivided conceptually into a sequence of octets of data followed by an end-of-TSDU indication. The T-DATA request primitive occurs when the end-of-TSDU indication is entered into the queue. The T-DATA indication primitive occurs when the end-of-TSDU indication is removed from the queue. This does not imply any particular subdivision in any real interface. The only objects which can be placed in a queue by the TS provider are disconnect objects (representing T-DISCONNECT primitives and their parameters). 0 TS user A, who initiates connection establishment by entering a connect object (representing a T-CONNECT request primitive) into the queue from A to B, is not allowed to enter any other object than a disconnect object into this queue until after the connect object representing the T-CONNECT confirm has been removed. In the queue from TS user B to TS user A, objects other than a disconnect object can be entered by TS user B only after TS user B has entered a connect object corresponding to a T-CONNECT response. The insertion of a disconnect object represents the initiation of the release procedure. The release procedure may be initiated at the times permitted in clause 14 and in the manner described in 11.2. The release procedure may be destructive with respect to other objects in the two queues. A queue relates an ordered set of distinct objects in the following ways: a) Queues are empty before a connect object has been added and can be returned to this state, with loss of their contents, by the TS provider under the circumstances as described in h) below. Objects are added to the queue, subject of control by the TS provider. Objects are normally removed from the queue, subject to control by the receiving TS user. Objects are normally removed in the same order that they were added [but see g) and h) below]. A queue has a limited capacity, but this capacity is not necessarily either fixed or determinable. The management of the queue capacity shall be such that normal data and end-of-TSDU indications cannot be added to the queue when its addition would prevent addition of an expedited TSDU or disconnect object. b) c) d) e) f) ITU-T Rec. X.214 (1993 E) 5 SIST EN ISO/IEC 8072:1998



ISO/IEC 8072 : 1994(E) In addition the TS provider may manipulate pairs of adjacent objects in the queue to allow: g) Reordering The order of any pair of objects may be reversed if, and only if, the following object is of a type defined to take precedence over the preceding object. Expedited TSDUs take precedence over octets of normal data and end-of-TSDU indications (see Table 1). h) Deletion Disconnect objects take precedence over any other object, Any object other than a disconnect object may be deleted by the TS provider if, and only if, the following one is a disconnect object (see Table 1). If a connect object associated with a T-CONNECT request primitive is deleted in this manner, the disconnect object is also deleted. If a connect object associated with a T-CONNECT response primitive is deleted, the disconnect object is not deleted. Whether the TS provider performs actions of types g) and h) or not, will depend on the behaviour of the TS users and on the agreed Quality of Service. In general, if the objects are not removed from the queue due to flow control expressed by the receiving TS user, the TS provider shall, after some unspecified period of time, perform all permitted actions of types g) and h). NOTES I The internai mechanisms which support the operation of a queue are not visible in the Transport Service. A queue is one particular way of expressing the mutual interaction between primitives at different TSAPs. There may also be, for example: a) constraints on the local ability to invoke primitives; a b) A TC endpoint identification mechanism must be provided locally if the TS user and the TS provider need to distinguish between several TCs at a TSAP. All primitives must then make use of this identification mechanism to identify the TC to which they apply. This implicit identification is not shown as a parameter of the TS primitives, and must not be confused with the address parameters of the T-CONNECT primitives. service procedures defining particular sequencing constraints on some primitives. 2 Table 1 - Precedence table The queue object x Connect object has precedence over queue object y Connect object Octets of normal data End-of-TSDU indication Expedited TSDU - Disconnect object - - Not applicable. No No precedence exists. Yes Precedence exists. Disconnect object Octetsof 1 End-of-TSDU 1 Expedited normal indication TSDU data I No No Yes [see h)] No No Yes [see g)] Yes [see h)] No No Yes [see g)] Yes [see h)] No No No Yes [see h)] - - - No [see h)] 10 The term Quality of Service (QOS) refers to certain characteristics of a TC as observed between the endpoints. QOS is described in terms of QOS parameters. These parameters give TS users a method of specifying their needs, and give the TS provider a basis for protocol selection. Quality of connection-mode Transport Service 6 ITU-T Rec. X.214 (1993 E) SIST EN ISO/IEC 8072:1998



ISOAEC 8072 : 1994(E) The QOS is normally negotiated between the TS users and the TS provider on a per TC basis, using the T-CONNECT request, indication, response, and confirm TS primitives defined in clause 1 1. The QOS requested by the calling TS user may be made poorer either by the TS provider following the T-CONNECT request, or by the called TS user, following the T-CONNECT indication. In applying this to some QOS parameters this may mean that: a) a delay becomes longer; b) a throughput becomes lower; c) the error rate becomes higher; d) the priority becomes lower; e) the failure probability becomes higher. However the TC protection parameter remains unchanged by the TS provider. The so negotiated QOS values then apply throughout the lifetime of the TC. NOTE - Users of the Transport Service should be aware that there is no guarantee that the originally negotiated QOS will be maintained throughout the Transport Connection lifetime, and that changes in QOS are not explicitly signalled by the Transport Service provider. The view of QOS at each end of an established TC is always the same. This clause does not specify particular values, or classes of values, for the QOS parameters. Possible choices and default values for each parameter will normally be specified at the time of initial TS provider installation. The values for any or 0 all parameters may be fixed for a given TS provider, in which case QOS negotiation on a per TC basis is not required. When a QOS value is specified; the TS Piser may also indicate whether the request is an absolute requirement or whether a degraded value is acceptable. The QOS parameters include parameters which express TS performance and parameters which express other TS characteristics. The QOS parameters specified in this clause are defined below. A classification of the performance QOS parameters is shown in Table 2. Table 2 - Classification of performance QOS parameters Performance criterion I Speed Phase TC establishment TC establishment delay Data transfer Throughput Transit delay TC release TC release delay AccuracylReliability TC establishment failure probability (misconnection/TC refusal) Residual error rate (corruption, duplicationlloss) Resilience of the TC Transfer failure probability TC release failure probability 10.1 TC establishment delay TC establishment delay is the maximum acceptable delay between a T-CONNECT request and the corresponding T-CONNECT confirm primitive. NOTE -This delay includes TS user dependent components. 10.2 TC establishment failure probability TC establishment failure probability is the ratio of total TC establishment failures to total TC establishment attempts in a measurement sample. A TC establishment failure is defined to occur when a requested TC is not established within the specified maximum acceptable TC establishment delay as a result of misconnection, TC refusal, or excessive delay on the part of the TS provider. TC establishment attempts which fail as a result of error, TC refusal, or excessive delay on the part of a TS user are excluded in calculating the TC establishment failure probability. ITU-T Rec. X.214 (1993 E) 7 P SIST EN ISO/IEC 8072:1998



ISO/LEC 8072 : 1994(E) I 10.3 Throughput Throughput is defined, for each direction of transfer, in terms of a sequence of at least two successfully transferred TSDUs. Given such a sequence of n TSDUs, where n is greater than or equal to two, the throughput is defined to be the smaller of: the number of TS user data octets contained in the last n-1 TSDUs divided by the time between the first and last T-DATA requests in the sequence; and the number of TS user data octets contained in the last n-1 TSDUs divided by the time between the first and last T-DATA indications in the sequence. Successful transfer of the octets in a transmitted TSDU is defined to occur when the octets are delivered to the intended receiving TS user without error, in the proper sequence, prior to release of the TC by the receiving TS user. Throughput is only meaningful for a sequence of complete TSDUs and each specification is based on a previously stated average TSDU size. Throughput is specified separately for each direction of transfer on a TC. In each direction, a specification of throughput will consist of a maximum throughput and an average throughput value. The maximum throughput value represents the maximum rate at which the TS provider can continuously accept and deliver TSDUs, in the absence of sending TS user input delays or flow control applied by the receiving TS user. Thus, the sequence of TSDUs in the calculation above are defined to be
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