SNAX/APN Application Programming Manual

The SNALU Interface
SNAX/APN Application Programming Manual—420111-001
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Remote PLU Initiates Session With SNALU
Application
Remote PLU Initiates Session With SNALU Application
When the SNALU application is the SLU, it may open the SNALU LU, issue a
WRITEREAD, and wait for an unsolicited BIND request from the PLU. This is called
SLU Accept mode.
For illustrations of situations in which SLU Accept is used, see Appendix C, Logic
Flows and Internal Formats When Using SNALU.
BIND Image Processing
The SNALU application accepts an incoming BIND image in the read portion of a
WRITEREAD call. It recognizes the incoming BIND image by the session-control
indicators in the RH and by finding X’31’ (the BIND request code) in byte 9 of the
application’s buffer. The SNALU application should check at least the following fields
to verify that they contain acceptable values:
The encoding method used for specifying maximum RU sizes is shown in the IBM
Systems Network Architecture: Format and Protocol Reference: Architectural Logic
manual.
Exchanging Data
Preceding subsections explored the mechanics of LU-LU session initiation. Once a
session is begun, the SNALU application must deal with SNA functions like normal and
expedited flow transmission, sequence number maintenance, chaining, bracketing,
pacing, and request/response modes.
SNA functions are described in the IBM manual Systems Network Architecture: Network
Product Formats or Systems Network Architecture: Format and Protocol Reference:
Architectural Logic manual.
Sequence Numbers
The Transmission Services (TS) profile specified in the BIND request that initiates an
LU-LU session determines whether or not sequence numbers are to be used during the
course of the session.
It is the responsibility of the application on the Tandem system to set the SNAX header
sequence number field properly for outgoing BIUs and to examine it for incoming BIUs.
The use of sequence numbers is described in detail in the IBM Systems Network
Architecture: Format and Protocol Reference: Architectural Logic manual.
Byte Number Within Buffer Content
19 Maximum RU size sent on normal flow by SLU
20 Maximum RU size sent on normal flow by PLU
Caution. For LU-LU sessions, sequence numbers must be used.