Envoy Application Programming Manual

BISYNC Point-To-Point Protocol
Envoy Application Programming Manual—427159-001
3-55
ID Exchange
ID Exchange
The use of an ID exchange on a switched line permits the stations to verify that they
each have a valid authorization. In the next example (Example 3-22), both the local and
remote stations are Compaq systems. The local station is the caller. The conversational
exchange shows the file-system calls and the control sequences associated with an ID
exchange sequence.
Note that the application process at the remote station could make three other valid
responses:
•
DLE EOT: This is a disconnect sequence, meaning that the ID is unsatisfactory. If
this is returned, the WRITEREAD by the caller completes with line state =
DISCONNECT, error = 164.
Example 3-22. ID Exchange Sequence
Local (caller) Remote (called)
(LITERAL ENQ = 5;) (LITERAL DLE = %20;)
(DEFINE ACK0 = DLE, “Q” A;)
(connection established) (connection established)
(format my ID:
buf ‘:=’ ID FOR idlen & ENQ:) CALL READ
|
(send ID) |
CALL WRITEREAD (buf) |
| ID ENQ --> (READ completes)
| error = 0
| line state = CONTROL
|
| (verify ID: ID is OK)
| (format my ID:
| buf ‘:=’ ID FOR idlen & ACK0:)
|
| (send ID)
| CALL WRITEREAD (buf)
(WRITEREAD completes) <-- ID ACK0 |
error = 0 |
line state = WRITE |
|
(verify ID: ID is OK) |
|
(send first message |
CALL WRITE |
| message 1 --> (WRITEREAD completes)
| error = 0
v line state = READ