HP 800 HP DLPI Programmer's Guide - Page 49

Figure 1-27 Figure 1-28 Introduction to DLPI DLPI Services Connectionless Data Transfer The connectionless data transfer service provides for the exchange of user data (DLSDUs) in either direction or in both directions simultaneously without having to establish a data link connection. Data transfer is neither acknowledged nor confirmed, and there is no end-to-end flow control provided. As such, the connectionless data transfer service cannot guarantee reliable delivery of data. However, a specific DLS provider can provide assurance that messages will not be lost, duplicated, or reordered. DL_UNITDATA_REQ conveys one DLSDU to the DLS provider. DL_UNITDATA_IND conveys one DLSDU to the DLS user. The normal flow of messages is illustrated in Figure 1-27. Message Flow: Connectionless Data Transfer DL_UNITDATA request DL_UNITDATA indication Error Reporting Service The connectionless-mode error reporting service may be used to notify a DLS user that a previously sent data unit either produced an error or cannot be delivered. This service does not, however, guarantee that an error indication will be issued for every undeliverable data unit. Connectionless-Mode Error Reporting DL_UDERROR indication Chapter 1 49