HP 800 HP DLPI Programmer's Guide - Page 44

Introduction to DLPI DLPI Services Figure 1-19 Data Transfer Service The connection-mode data transfer service provides for the exchange of user data in either direction or in both directions simultaneously between DLS users. Data is transmitted in logical groups called data link service data units (DLSDUs). The DLS provider preserves both the sequence and boundaries of DLSDUs as they are transmitted. Normal data transfer is neither acknowledged nor confirmed. It is up to the DLS users, if they so choose, to implement a confirmation protocol. Each DL_DATA_REQ primitive conveys a DLSDU from the local DLS user to the DLS provider. Similarly, each DL_DATA_IND primitive conveys a DLSDU from the DLS provider to the remote DLS user. The normal flow of messages is illustrated in Figure 1-19. Message Flow: Normal Data Transfer DL_DATA request DL_DATA indication Connection Release Service The connection release service provides for the DLS users or the DLS provider to initiate the connection release. Connection release is an abortive operation and any data in transit (not been delivered to the DLS user) may be discarded. 44 Chapter 1