Envoy Application Programming Manual

BISYNC Multipoint Tributary Protocol
Envoy Application Programming Manual—427159-001
5-5
Station Addresses
When the application process can accept data, the action is similar to an application
process acting as a tributary station:
1. To indicate the ability to accept data, the application process sets the station’s select
state to active by calling the CHANGELIST procedure.
2. When the station is selected, the outstanding READ completes with a no-error
indication. The first message from the supervisor station is returned in the buffer
specified in the READ call.
3. The tributary station must then call READ for each additional message from the
supervisor station.
4. Messages are read until a message ending with an ETX character is received. The
application process then sets the station’s select state to inactive and initiates another
READ on the line. This READ receives the EOT sequence from the supervisor
station.
5. Envoy then again monitors the line. The READ remains outstanding (does not
complete) until the station has data to send and is polled or is willing to accept data
and is selected.
Figure 5-2
on page 5-6 shows BISYNC multipoint tributary selection.