Envoy ACP/XF Application Programming Manual

Normal Response Mode (NRM) Protocols
EnvoyACP/XF Application Programming Manual–132179
3-48
SDLC and ADCCP-NRM Nonswitched Multipoint
Operation
SUPERVISOR TRIBUTARY
CALL CONTROL(pnum,13,0); CALL READ(snum,
IF <> THEN CALL ERROR^PROC; read^buf1,2);
CALL AWAITIO (pnum); IF <> THEN CALL ERROR^PROC;
IF <> THEN CALL ERROR^PROC; CALL READ (snum,
read^buf2,2);r);
IF <> THEN CALL ERROR^PROC;
CALL AWAITIO (snum);
IF <= THEN CALL ERROR^PROC;
CALL AWAITIO (snum);
IF <= THEN CALL ERROR^PROC;
For each station address in the tributary process, the AWAITIO associated with the first
READ request completes indicating a CCG condition code, a SNRM code (%20) in
MCW.<3:7> of the read buffer, and the station address in MCW.<8:15> of the read
buffer.
At this point, the supervisor begins polling the tributary stations. All the tributary
stations post a READ call to accept any I-frames or U-frames sent to them by the
supervisor. The maximum frame size was defined as 256 octets (128 words), so all the
READ calls request 258 octets (two additional octets for the MCW).
When the supervisor needs to send an I-frame or a U-frame to one of the tributaries, the
supervisor formats a write buffer with the tributary address in MCW.<8:15> then issues
a WRITE call. When a tributary needs to send an I-frame or a U-frame to the supervisor,
the tributary formats a write buffer with its own tributary address in MCW.<8:15> then
issues a WRITE call. The supervisor can transmit application WRITE requests as soon
as the line can handle it. Tributary WRITE requests are queued until the station is
polled.
Because the actual use of READ loops, WRITE loops, and WRITEREAD procedures
varies from one application to another, the following line activity is shown without a
corresponding application-level code sequence. The diagram shows what EnvoyACP/XF
does at the link level in response to various I/O calls.
In the example below, the supervisor polls station A, which has two I-frames to transmit.
(After the primary station posts the initial READ, EnvoyACP/XF begins polling the
tributaries.)
The supervisor accepts and acknowledges the I-frames, then polls station B. B has
nothing to send.
At that point, the supervisor application issues a sequence of five WRITE requests to
station B. EnvoyACP/XF interrupts polling so the supervisor can transmit the five
frames. When station B acknowledges the final frame, polling resumes at the point at
which it was interrupted.
Transmission frames generated automatically by EnvoyACP/XF and the CLIP are
enclosed in brackets.
SUPERVISOR TRIBUTARIES
[A,RR,P] —————————————>
<————————— line turnaround
<————————— A,I-Nr(0),Ns(0)