Specifications

Interfaces
Page
14
. .
maintenance operations.
From the perspective of maintenance operations, there are two data
link configurations:
~oint-to-point and multiaccess.
Point-to-point data links are those where there
is a single node on
the each end of a loqical channel. Transits and receives are always
between these two nodes. Multipoint is treated as point-to-point, in
the sense that each logical channel (tributary)
is identified and used
independently.
Multiaccess data 1,inks are those where the number and identification
of all adjacent nodes are not necessarily known. On multiaccess data
links, node identification must accompany transmit and receive
requests. Additionally, multiaccess data links may provide multicast
; service for communications with a class of nodes.
Independently of configuration, some data links may allow concurrent
operation of both normal and maintenance traffic. Others may allow
maintenance traffic only in a mode that excludes normal traffic.
This interface assumes that all data links offer the same basic
services, framing and error checking. The data link frames messages
and provides the length of received messages. Messages are sent and
received in the order they were offered by the sender. Messages that
the data link delivers to the receiver have been checked for bit
errors. It is possible for messages
tu be lost with no notification
to either sender or receiver.
The interface function descriptions refer to data link configuration
and maintenance exclusiveness
as necessary to indicate differences of
operation.
The Data Link Interface contains the following functions:
. Maintenance-check -- check to see if maintenance service is
needed.
. Open -- open a port.
. Close -- close a port.
. Transmit -- send a frame.
, Transmit-pol1 -- check for completion of a Transmit.
. Receive -- receive a frame.
. Receive-poll -- check for completion of a Receive.
. Receive-abort -- abort a Receive.