HP 800 HP DLPI Programmer's Guide - Page 23

Chapter 1 Introduction to DLPI The Data Link Layer Connection-mode Service The connection-mode service is characterized by the following four phases of communication: • Local Management • Connection Establishment • Data Transfer • Connection Release Local Management This phase enables a DLS user to initialize a stream for use in communication and establish an identity with the DLS provider. Connection Establishment This phase enables two DLS users to establish a data link connection between them to exchange data. One user (caller) initiates the connection establishment procedures, while another user (callee) waits for incoming connect requests. The callee is identified by an address associated with its stream. A callee may either accept or deny a request for a data link connection. If the request is accepted, a connection is established between the DLS users, and they enter the data transfer phase. For both the caller and callee, only one connection may be established per stream. Thus, the stream is the communication endpoint for a data link connection. The callee may choose to accept a connection on the stream where it received the connect request, or it may open a new stream to the DLS provider and accept the connection on this new, responding stream. By accepting the connection on a separate stream, the initial stream can be designated as a listening stream through which all connect requests will be processed. As each request arrives, a new stream (communication endpoint) can be opened to handle the connection, enabling subsequent requests to be queued on a single stream until they can be processed. Data Transfer In this phase, the DLS users are considered peers and may exchange data simultaneously in both directions over an established data link connection. Either DLS user may send data to its peer DLS user at any time. Data sent by a DLS user is guaranteed to be delivered to the remote user in the order in which it was sent. 23