DLPI Programmer's Guide

94 Chapter 2

DLPI Primitives

Connection-mode Service Primitives

This section describes the service primitives that support the

connection-mode service of the data link layer. These primitives support

the establishment of connections, connection-mode data transfer, and

connection release services.

In the connection establishment model, the calling DLS user initiates a

request for a connection, and the called DLS user receives each request

and either accepts or rejects it. In the simplest form, the called DLS user

is passed a connect indication and the DLS provider holds any

subsequent indications until a response for the current outstanding

indication is received. At most one connect indication is outstanding at

any time.

DLPI also enables a called DLS user to multi-thread connect indications

and responses. The DLS provider will pass all connect indications to the

called DLS user (up to some pre-established limit as set by

DL_BIND_REQ and DL_BIND_ACK). The called DLS user may then

respond to the requests in any order.

To support multi-threading, a correlation value is needed to associate

responses with the appropriate connect indication. A correlation value is

contained in each DL_CONNECT_IND, and the DLS user must use this

value in the DL_CONNECT_RES or DL_DISCONNECT_REQ primitive

used to accept or reject the connect request.

Once a connection has been accepted or rejected, the correlation value

has no meaning to a DLS user. The DLS provider may reuse the

correlation value in another DL_CONNECT_IND.

Connection-Oriented DLPI Extensions

These primitives are only valid on connection-oriented DLPI STREAMS.

Connection-oriented DLPI streams are those on which a DL_BIND_REQ

with dl_service_mode set to DL_CODLS has been done.

DL_HP_INFO_REQ

Requests the DLS provider to provide information on the state of the

connection on a DLPI stream.