Envoy Application Programming Manual

BISYNC Point-To-Point Protocol
Envoy Application Programming Manual—427159-001
3-52
Limited Conversational Mode
In the next example of conversational exchange (Example 3-20), the local station is the
sender and the remote station is the receiver. The local station makes all transmissions
with calls to the WRITEREAD procedure. This use of the WRITEREAD procedure
allows the remote station the option of replying to each message. (This option might be
used to report an error condition to the local station.)
The conversational exchange shows the control sequences associated with sending
messages with WRITEREAD calls to the remote station and a conversational reply by
the remote station.
Example 3-20. Send Messages with WRITEREAD Calls
Local Remote
line state = CONTROL line state = CONTROL
CALL WRITEREAD CALL READ
| ENQ --> |
| <-- ACK0 |
| message 1 --> (READ completes)
| error = 0
| line state = READ
|
| (message checked: no
| discrepancy found)
| CALL READ
(WRITEREAD completes) <-- ACK1 |
error = 0 |
line state = WRITE |
|
CALL WRITEREAD |
| message 2 --> (READ completes)
| error = 0
| line state = READ
|
| (message checked:
| discrepancy found)
| CALL WRITEREAD
(WRITEREAD completes) <-- message 3 |
error = 0 |
line state = READ |
|
(process the reply) |
CALL WRITEREAD |
| message 4 --> (WRITEREAD completes)
| error = 0
| line state = READ
|
| CALL READ
(WRITEREAD completes) <-- ACK1 |
error = 0 |
line state = WRITE v