DLPI Programmer's Guide

44 Chapter 1
Introduction to DLPI
DLPI Services
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.
Figure 1-27 Message Flow: Connectionless Data Transfer
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
could not be delivered. This service does not, however, guarantee that an
error indication will be issued for every undeliverable data unit.
Figure 1-28 Connectionless-Mode Error Reporting
Raw-mode Services
The raw-mode services enable a DLS user to transfer packets containing
complete MAC and LLC headers to a peer DLS user. The raw-mode
service does not guarantee reliable delivery of data units between peer
DLS users (e.g. lack of flow control may cause buffer resource shortages
that result in data being discarded).
The DLS user requests the raw-mode services by setting the service
mode in the DL_BIND_REQ to DL_HP_RAWDLS.
DL_UNITDATA
request
DL_UNITDATA
indication
DL_UDERROR
indication