DLPI Programmer's Guide

18 Chapter 1

Introduction to DLPI

The Data Link Layer

Figure 1-1 Abstract View of DLPI

The data link interface is the boundary between the network and the

data link layers of the OSI Reference Model. The network layer entity is

the user of the services of the data link interface (DLS user), and the

data link layer entity is the provider of those services (DLS provider).

This interface consists of a set of primitives that provide access to the

data link layer services, plus the rules for using those primitives (state

transition rules). A data link interface service primitive might request a

particular service or indicate a pending event.

To provide uniformity among the various UNIX system networking

products, an effort is underway to develop service interfaces that map to

the OSI Reference Model. A set of kernel-level interfaces, based on the

STREAMS development environment, constitute a major portion of this

effort. The service primitives that make up these interfaces are deﬁned

as STREAMS messages that are transferred between the user and

provider of the service. DLPI is one such kernel-level interface, and is

targeted for STREAMS protocol modules that either use or provide data

link services. In addition, user programs that wish to access a

STREAMS-based data link provider directly may do so using the

putmsg(2) and getmsg(2) system calls.

Referring to Figure 1-1, the DLS provider is conﬁgured as a STREAMS

driver, and the DLS user accesses the provider using open(2) to establish

a stream to the DLS provider. The stream acts as a communication

Data Link

User

Request/Response

Primitives

Indication/Confirmation

Primitives

Data Link

Provider

DLPI