Envoy Application Programming Manual

BISYNC Multipoint Tributary Protocol
Envoy Application Programming Manual—427159-001
5-3
Station Addresses
select state active. You specify the initial states of these bits when you create the address
list (prior to calling DEFINELIST). After passing the address list to Envoy, you can
subsequently alter the state of these bits by calling the CHANGELIST procedure.
The typical method of operation for an application process acting as a tributary station is
as follows:
1. Initially, the application process sets the poll and select states of all stations to
inactive before passing the address list to Envoy.
2. The application process initiates a nowait READ on the line. This READ remains
outstanding until either a station that has data to send is polled or a station that is
able to accept data is selected.
3. While the READ is outstanding and the poll and select states of the stations are
inactive, Envoy responds to polling or selection; the application process executes
concurrently. If the application process does not have a READ outstanding, Envoy
does not respond and the supervisor station assumes that the station is off line.
4. When a tributary station has data to send, the application process sets that station’s
poll state to active by calling the CHANGELIST procedure.
5. When the station is polled again, the outstanding READ completes with an error 166
(address has been polled).
6. The application process then calls the WRITE procedure one or more times to send
the data to the supervisor station.
7. When the transmission is complete, the application process calls the CHANGELIST
procedure to set the station’s poll state to inactive and then initiates another READ
on the line (this READ causes an EOT indication to be sent to the supervisor
station).
Figure 5-1
on page 5-4 shows BISYNC multipoint tributary polling.