SNAX/HLS Application Programming Manual

Life Cycle of a Session
Sessions
3–8 104707 Tandem Computers Incorporated
If the LARGE–MESSAGE–OPTION is enabled using the LMO PROFILE attribute in
the RDT, your application program must be engaged in the chaining operations. In
particular, on the sending side, your application program must:
Deliver data to SNAX/HLS in units not larger than the BIND–specified maximum
RU–size
Indicate end–of–messages (SNA end-of-chains) explicitly by setting the
MESSAGE–COMPLETE–IND
Adhere to the SNA restriction that the END–TRANSACTION–IND can be
specified as Y only on the first element of a chain
Avoid the use of SEND–AND–RECEIVE–DATA on half–duplex sessions except at
the end of the message (MESSAGE–COMPLETE–IND = Y).
On the receiving side, your program must:
Detect message boundaries by watching the MESSAGE–COMPLETE–IND
Handle message cancelations
Notification SNAX/HLS allows the application to specify that a notification of receipt be generated
for messages it sends. This notification confirms the actual receipt of the response to
the request your application just sent. The particular mechanism used to indicate the
notification depends upon an aspect of the SNA session rules, known as immediate or
delayed request mode.
Immediate Request Mode
In immediate request mode, your session can have at most one pending notification.
In other words, your application program can do nothing until the notification is
received. SNAX/HLS reacts to this condition by postponing the completion of the
SEND–DATA verb until the notification arrives. If the verb was a
SEND–AND–RECEIVE–DATA verb, and the notification was positive, the notification
is discarded and the verb is transformed into the RECEIVE–DATA verb.
Delayed Request Mode
In delayed request mode, your session can have many notifications pending. Thus,
the SEND–DATA verb completes as soon as the data is sent. No delay occurs awaiting
the notification from your partner. When that notification arrives, an internal record
of the notification is made and the notification is delivered on a subsequent receive
type verb. The correlation of the response to the original message is an application
responsibility, using the recovery tags on the initial reply to the SEND–DATA request
and the message tag on the response.