SNAX/HLS Configuration and Control Manual

Step 3. Planning Session BINDs
Planning the SNAX/HLS Environment
2–14 104705 Tandem Computers Incorporated
Maximum RUs
These fields select the maximum-length message segment to be transmitted between
session partners. SNAX/HLS permits a maximum length of 30720 bytes, but some
devices and some IBM products require smaller chunks of the message to be
transmitted. Set these fields to match the device controller or the IBM product
configuration.
Appendix A shows how maximum RU sizes are encoded in BIND messages. Only
those values supported by SNAX/HLS are shown. For example, if the device specifies
that only 512 bytes of a user message be buffered in any one message segment, select
512 as the maximum RU to be sent by the primary session partner. If the SNAX/HLS
application sends a 1034-byte message, the SNAX/HLS server transmits it to the
session partner in three segments (that is, chain elements of 512, 512, and 10 bytes).
SNAX/HLS uses the maximum receive RU size to determine the size of the read it
issues to SNAX/XF or SNAX/CDF. Because each outstanding read occupies space in
the process file segment (PFS), maximum receive RU size should be no larger than
needed.
Excessive values would waste PFS space and thereby limit the number of sessions that
one instance of SNAX/HLS can support. Neither should RU size be too small, because
the smaller size, while maximizing the number of sessions supportable by
SNAX/HLS, also reduces throughput by forcing messages to be split into segments.
Using segments smaller than 256 bytes yields no advantage, because the minimum
space allocated for an RU by SNAX/HLS is 256 bytes.
If the maximum RU size is large and the number of concurrent SNAX/HLS sessions is
also large, you can exhaust the PFS. To avoid this, you can specify the TWOSTEP
configuration parameter, directing SNAX/HLS to use two-step reads.
If the large message option (LMO) is used, the RU sizes must be sufficient to include
all FMH data in the first RU.
In the BIND message, the maximum RU size that can be sent by the primary is
indicated in byte 11, and the maximum RU size that can be sent by the secondary is
indicated in byte 10. In HLSRDT, these attributes are specified by the BIND attributes
PRI-MAX-RU and SEC-MAX-RU, respectively.
PS Profile These fields select a range of device-display/data-formatting capabilities. Set the
LU-LU session type to a valid session type as needed by the partner and set the
cryptographic fields appropriately. The contents of these fields are neither processed
nor validated by SNAX/HLS. (See the SNA references listed in the Preface.)
LU Type
The LU type is not interpreted by SNAX/HLS. In the BIND message, the LU type is
indicated in byte 14. In HSLRDT, this attribute is specified by the BIND attribute,
LU-SESSION-TYPE.