Envoy Application Programming Manual

Burroughs Point-To-Point Protocol
Envoy Application Programming Manual—427159-001
9-12
WRITE Procedure
The file-system errors that may occur on an initial READ in a WRITE state are the same
as those for an initial READ in a CONTROL state.
WRITE Procedure
The WRITE procedure is used to select and transmit messages to a tributary station.
While messages are being sent, the line is in the WRITE state. The line returns to the
CONTROL state when the supervisor station sends an EOT sequence (to indicate the
completion of the transmission).
Initial WRITE (Line in CONTROL State)
An initial WRITE causes Envoy, on behalf of the application process, to bid for the line
(Example 9-4). If the remote station acknowledges the line bid, the message in the buffer
of the application process is transmitted to the remote station. The call to the WRITE
procedure completes when the remote station acknowledges the message. The successful
transmission of the initial message is indicated by a condition code of CCE upon
completion of the WRITE. Following transmission of the initial message, the line is in
the WRITE state.
Example 9-3. Initial READ (Line in WRITE State)
Local Remote
line state = WRITE
CALL READ(...)
| EOT -->
| <-- ENQ (bid)
| ACK -->
| <-- message
(READ completes)
error = 0
line state = READ
Example 9-4. Initial WRITE (Line in CONTROL State)
Local Remote
line state = CONTROL
CALL WRITE(...)
| (bid) ENQ -->
| <-- ACK
| message -->
| <-- ACK
(WRITE completes)
error = 0
line state = WRITE