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Technical Standard: Networking Services (XNS), Issue 5.2 Draft 2.0
Copyright © 1999 The Open Group

General Introduction to the XTI

Support for XTI as defined in this Part 3 of the XNS Technical Standard is optional. The XTI interface is obsolete. Writers of new applications using the Internet protocol suite are recommended to use sockets rather than XTI. Where protocols for which there is no sockets support are in use, XTI is still recommended in preference to proprietary APIs.

The X/Open Transport Interface (XTI) specification defines an independent transport-service interface that allows multiple users to communicate at the transport level of the OSI reference model. The specification describes transport-layer characteristics that are supported by a wide variety of transport-layer protocols. Supported characteristics include:

Although all transport-layer protocols support these characteristics, they vary in their level of support and/or their interpretation and format. For example, there are transport-level options which remain constant across all transport providers while there are other options which are transport-provider specific or have different values/names for different transport providers.

The main Chapters in this Part 2: XTI specification describe interfaces, parameters and semantics constant across all transport providers. Several Appendices provide information that is not an integral part of the main body since it is either descriptive or applies only to some transport providers.

Some appendices provide information pertinent to writing XTI applications over specific transport providers. The transport providers fall into three classes:

While XTI gives transport users considerable independence from the underlying transport provider, the differences between providers are not entirely hidden. Guidelines for Use of XTI includes guidelines for writing transport-provider-independent software, which can be done primarily by using only functions supported by all providers, avoiding option management, and using a provider-independent means of acquiring addresses.

While the transport-provider-specific Appendices are intended mostly for transport users, they are also used by implementors of transport providers. For the purposes of the implementors, some of the Appendices show how XTI services can be mapped to primitives associated with the specific providers. These are provided as guidance only and do not dictate anything about a given implementation.

Some of the Appendices to the XTI specification are included as vehicles for communicating information needed by implementors, or guidelines to the use of the specification in question. The Guidelines for the use of XTI (see Guidelines for Use of XTI), Minimum OSI Functionality (see Minimum OSI Functionality), (Appendix H), SNA transport provider (see SNA Transport Provider), SPX/IPX transport provider (see IPX/SPX Transport Provider), and Comparison of XTI to TLI (see XTI and TLI) all belong to this category.

Some other Appendices, however, have evolved into a prescriptive specification, as in the case of the ISO transport provider (see Use of XTI with ISO Transport Protocols), and the NetBIOS transport provider (see Use of XTI to Access NetBIOS).

Since not every XTI implementor would find it relevant to implement the functionality of all of these Appendices, they have been kept separate from the definitions for XTI. Thus they are readily identifable as brandable XTI options. Support for these transport providers is declared in Branding documentation through the XTI Conformance Statement Questionnaire.

Topics beyond the scope of the XTI specification include:

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