SNAX/HLS Configuration and Control Manual

Step 1. Partner Requirements Planning
Planning the SNAX/HLS Environment
104705 Tandem Computers Incorporated 2–3
Use of Function Management Headers (FMHs)
Some programmable controllers require the use of FMHs. (See the SNA references
listed in the Preface.) The program in the controller determines this requirement. The
use of FMHs is fully supported by SNAX/HLS. The SNAX/HLS application is
responsible for placing the FMH in the buffer of a message to be sent and for analyzing
any FMH returned in the reply buffer. See the SNAX/HLS Application Programming
Manual for information on indicating formatted data to SNAX/HLS. The FMH
formats must be understood by the application staff before programming begins.
Certain LU type 0 implementations use a nonstandard FMH convention where no
continuation of FMHs is allowed. CICS controlling an IBM 3600 is an example. Such
applications might require the use of the SINGLE-FMH PROFILE attribute.
Special SNA Requests
SNAX/HLS provides a generic high-level interface for SNA devices. Not all SNA
requests can be generated or processed by SNAX/HLS applications. SNAX/HLS
neither sends nor processes CHASE messages.
SNAX/HLS does support quiesce protocols (QEC, QC, and RELQ) and can send and
receive bracket initiation message RTR. It can also receive SBI and BIS.
Device SNA Protocol Requirements
Many controllers are governed by a control program (CP) residing in firmware. Such
CPs can often be customized by an installation procedure. The IBM 3274 Control Unit
is one such controller. You must be sure the control program respects the BIND sent
by the application. In planning the BIND, take into account the CP/AP requirement
on DFC send/receive mode (half duplex and full duplex), bracket usage, and SNA
response type (for example, DR1, DR2, or DR3).
Some application programs use the specific configuration of DR and ER bits to convey
important information. For example, when a transaction is submitted to IMS
FASTPATH that it cannot immediately answer, it sends a null result. The ERI bit on
that result dictates whether the application should issue an RTR
(HLS-FLOW-CONTROL(RT)) to obtain the “real” response. If the value of the ERI bit
on inbound requests is important to your application, make sure that the PROFILE
elects the ENCODE-ERI PROFILE attribute.
Gateway System Planning In gateway applications, the SNAX/HLS application communicates with an IBM
application (for example, CICS or IMS). The same issues discussed above for devices
are relevant here. The main difference is that the IBM application is configured as
though the SNAX/HLS application were a device. To support an IBM host
application, consider the points discussed in the following paragraphs.