Data Link Provider Interface (DLPI), Version 2
Copyright © 2000 The Open Group


Open Group Technical Standard
Data Link Provider Interface (DLPI), Version 2
Document Number: C811
ISBN: 1-85912-251-5

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This Document
The Open Group first published a Data Link Provider Interface (DLPI) specification in February 1997 (CAE Specification number C614). This document is the DLPI Version 2 Technical Standard, and it supersedes C614.

The DLPI standard specifies a STREAMS kernel-level instantiation of the ISO Data Link Service Definition ISO/IEC 8886 and Logical Link Control ISO/IEC 8802-2 (LLC). Where the two standards do not conform, ISO/IEC 8886 prevails.

The DLPI enables a data link service user to access and use any of a variety of conforming data link service providers, without requiring special knowledge of the provider's protocol.

Specifically, the interface is intended to support X.25 LAPB, BX.25 level 2, SDL C, ISDN LAPD, Ethernet, CSMA/CD, FDDI, token ring, token bus, Bisync, Frame Relay, Native ATM Services (see Referenced Documents), Fiber Channel and HIPPI. Readers should note that the list of data links supported by the interface may be augmented and is published on the World-Wide Web at, which is DLPI Corrigendum U019. (see under Ordering Information). This Corrigendum will periodically be updated to add relevant information such as recognised implementors' agreements/guidelines for common data link providers.

Among the expected data link service users are implementations of the OSI network layer and SNA path control.

The interface specifies access to data link service providers, and does not define a specific protocol implementation. Thus, issues of network management, protocol performance, and performance analysis tools are beyond the scope of this document and should be addressed by specific implementations of a data link provider. However, accompanying each provider implementation should be information that describes the protocol-specific behavior of that provider. Currently, there are plans to come up with a set of implementors' agreements/guidelines for common data link providers. These agreements will address issues such as DLSAP address space, subsequent addresses, ppa access and control, QOS, supported services etc.

Intended Audience
This specification assumes the reader is familiar with OSI Reference Model terminology, OSI Data Link Services, and STREAMS.
Document Structure

A Glossary and Index are also provided.

Typographical Conventions
The following typographical conventions are used throughout this document:

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The base document from which this specification is derived was published as Copyright 1991 UNIX International, Inc.

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Referenced Documents

The following documents are referenced in this specification:

ATM Services

Native ATM Services. See the ATM Forum Publication AF-SAA-API-DLPI-0091.000: "Native ATM Services Data Link Provider Interface (DLPI) Addendum Version 1.0". This publication is available at, in the following files:
af-saa-api-dlpi-0091.000.pdf (PDF) (Postscript)

ISO/IEC 8886

ISO/IEC 8886:1996, Information Technology - Open Systems Interconnection - Data Link Service Definition.

ISO/IEC 8802-2

ISO/IEC 8802-2:1994, Information Technology - Telecommunications and Information Exchange between Systems - Local and Metropolitan area Networks - Specific Requirements - Part 2: Logical Link Control.


UNIX Press (A Prentice Hall Title) book "STREAMS Modules and Drivers", published 1992, ISBN 0-13-066879-6.


CCITT Recommendation X.200, "Reference Model of Open Systems Interconnection for CCITT Applications", 1984.

XNS, Issue 5

CAE Specification, February 1997, Networking Services, Issue 5 (ISBN: 1-85912-165-9, C523), published by The Open Group.

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