Envoy Application Programming Manual

BISYNC Multipoint Tributary Protocol
Envoy Application Programming Manual—427159-001
5-28
CONTROL Procedure (Send EOT)
The file-system errors for a continuation WRITEREAD are the same as those for a
continuation WRITE.
Initial WRITEREAD (Line in READ State, Last State is
CONTROL or WRITE)
A WRITEREAD while the line is in the READ state is used to acknowledge a message
from the supervisor by returning a message. The action of an initial WRITEREAD while
the line is in the READ state is the same as that for a call to WRITEREAD while the
line is in the WRITE state.
Continuation WRITEREAD (Line in READ State, Last State is
READ)
This operation is not permitted. A second call to WRITEREAD while the line is in the
READ state would be an attempt to acknowledge two consecutive messages with
messages. This is not permitted for limited conversational mode according to the
BISYNC protocol.
A call to WRITEREAD if the line is in the READ state and the last state is READ
completes with a condition code of CCL and an error 160 (request is invalid for device
state; protocol error).
CONTROL Procedure (Send EOT)
The EOT sequence is used prior to relinquishing line control. The application sends
EOT by calling the CONTROL procedure and specifying operation 13 (Example 5-10).
The send EOT operation should not be used to relinquish control of the line after error
conditions have been detected.
Example 5-9. Possible Line States After Continuation WRITEREAD
Tributary (Local) Supervisor (Remote)
line state = WRITE
CALL WRITEREAD (...)
| message n -->
|
| <-- ACKn or
(WRITE completes) message 1
If ACKn received, line state = WRITE.
If message received, line state = READ.
Example 5-10. CONTROL Procedure (Send EOT)
CALL CONTROL (fnum,13)
| EOT -->
(CONTROL completes)
error = 0 line state = CONTROL