Envoy Application Programming Manual

BISYNC Multipoint Tributary Protocol
Envoy Application Programming Manual—427159-001
5-22
READ Procedure
Note that the initial message from the supervisor is not acknowledged by the initial
READ. The following READ acknowledges the initial message.
Table 5-9
lists the file-system errors that may occur on an initial READ.
Example 5-4. Initial READ (Line in CONTROL Active State)
Tributary (Local) Supervisor (Remote)
line state = CONTROL
all select addresses = inactive
CALL READ(...)
| <-- EOT SYN-sel addr 1-ENQ
| RVI -->
| <-- EOT SYN-sel addr 2-ENQ
| RVI -->
|
sel address 1 set active
using CHANGELIST
|
| <-- EOT SYN-sel addr 1-ENQ
| ACK0 -->
| <-- message 1
(READ completes)
error = 0
line state = READ
MCW.<1> = 1 (READ type = initial READ)
MCW.<8:15> contains entry number for station = sel addr 1
Table 5-9. Initial READ File System Errors (page 1 of 2)
Error State Description Resultant Line Number
0 No error. A station responded with a message.
Message is returned to the buffer of the applica-
tion process.
READ
160 Request is invalid for device state; protocol error. unknown
161 Impossible event occurred for line state. unknown
166 Address has been polled. The station indicated in
the entry number field of the message control
word was polled (the station’s poll state is active).
WRITE
172 Reply not proper for protocol. The data received
while waiting for a response to the poll sequence
was not proper for the BISYNC protocol.
CONTROL
173 Transmission error. The message received was in
error and a NAK sequence was sent the number
of times specified by the retry value.
CONTROL