SNAX/HLS Application Programming Manual

Life Cycle of a Session
Sessions
3–2 104707 Tandem Computers Incorporated
Opening Communication
With the Session Partner
The establishment of communication with the session partner is the result of executing
an HLS–OPEN verb or an OPEN–SESSION verb.
A session open
Establishes communication with the Tandem SNA access method (for example,
the SNAX/CDF process or the SNAX/XF line handler).
Possibly awaits a modem connect. (This is determined by rules given in the
PROFILE.)
Sends an INIT–SELF or BIND message to the partner (and awaits a reply), or
awaits an incoming CINIT or BIND message. This is determined by rules given in
the PROFILE.
Exchanging Data With the
Session Partner
Once a session is open, data traffic can flow between the session partners. The rules
governing this communication are dictated by the SNA rules specified in the BIND
message used to open the session. For the most part, the interaction between session
partners is transparent to the application; however, the application must comply with
the rules because a violation is detected as an error and will probably terminate the
session.
Preparing for an
Orderly Close
When the application wishes to stop the exchange of data, it issues a
PREPARE–TO–CLOSE verb. This initiates a shut down protocol according to SNA
rules that protects against the possible loss of data.
Closing Communication
With the Session Partner
Your application should use the PREPARE–TO–CLOSE verb to perform an orderly
shutdown. A session is closed by a SNAX/HLS application as the result of executing
an HLS–CLOSE verb or a CLOSE–SESSION verb. A session can also be closed by the
session partner.
Once a session is closed, communication with the session partner is no longer possible.
As long as the session remains allocated, however, messages from the operator can
still be generated with the HLSCOM QMSG command.
Deallocating the
Half-Session
The final event in a session is the deallocation of the resources used to sustain the half–
session. This results when the application executes an HLS–DEALLOCATE verb or a
CLOSE–SESSION verb.
Allocation and Deallocation The allocation of a half–session does not involve SNA activities. Given the name of the
intended partner, allocation provides a session ID (a 16-bit nonzero label) that the
application must preserve in order to proceed with the session. You should not
assume that the SESSION–ID values are assigned in any particular order.
Session Profiles
In addition to specifying the session partner’s name, the allocation operation specifies
the name of the PROFILE (the rules under which the session is to proceed). Profiles
are stored in the RDT (Resource Definition Table), which is maintained by your system
programmer or analyst (see Section 4 of the SNAX/HLS Configuration and Control
Manual).