HPRSESLM start option


   .-HPRSESLM--=--NOLIMIT------.   
>>-+---------------------------+-------------------------------><
   '-HPRSESLM--=--+-NOLIMIT--+-'   
                  +-sess_lim-+     
                  '-DISABLED-'

range:

NOLIMIT, DISABLED or 1000 - 2147483647

Rule: HPRSESLM is meaningful only if VTAM® provides RTP-level HPR support. At a minimum, the NODETYPE start option must also be coded and the RTP parameter must be specified on the HPR start option.

Use the HPRSESLM start option to limit the number of sessions that VTAM assigns to a single RTP connection (pipe). When the number of sessions assigned to an RTP pipe reaches the specified sess_lim value, new sessions are no longer assigned to that RTP pipe until the number of sessions falls below the specified sess_lim value; instead, another RTP pipe is chosen or created for the new sessions. Limiting the number of sessions on a single RTP pipe can result in significant performance improvement by allowing concurrent traffic on multiple RTP pipes.

HPRSESLM=NOLIMIT: Specifies that VTAM should not enforce a limit on the number of sessions assigned to an RTP pipe.
HPRSESLM=sess_lim: Specifies that VTAM should limit the number of sessions assigned to an RTP pipe to the number specified by the sess_lim value. The sess_lim value is a decimal integer in the range 1000 - 2147483647.
HPRSESLM=DISABLED: Specifies that VTAM should completely disable the HPRSESLM function to allow this level of VTAM to coexist with older releases of VTAM. HPRSESLM=DISABLED is meaningful only on interchange nodes (ICNs). If you specify HPRSESLM=DISABLED on any other type of APPN node, IST1070I is displayed and HPRSESLM is set to NOLIMIT.

If HPRSESLM is not set to DISABLED, then you can change the value of HPRSESLM (to any valid value except DISABLED) while VTAM is running by issuing the MODIFY VTAMOPTS command. If HPRSESLM is set to DISABLED, then you can only change the HPRSESLM value by stopping and restarting VTAM. Although changing HPRSESLM does not affect any sessions that have already been assigned to an RTP pipe, the changes to HPRSESLM take effect immediately. If you specify HPRSESLM=NOLIMIT , then VTAM does not enforce a session limit for all new and existing RTP pipes when new sessions are established. If you specify HPRSESLM=sess_lim, then VTAM immediately begins enforcing the specified session limit (for all new and existing RTP pipes) when new sessions are established.

The sess_lim value specified for HPRSESLM does not represent an absolute session limit. The actual number of sessions assigned to an RTP pipe can exceed the specified sess_lim value during normal operation.

If multiple sessions (that are between the same two APPN nodes and that are requesting the same class of service) are initiated at the same time, then most or all of these sessions can be assigned to the same RTP pipe and result in the specified sess_lim value being exceeded. This is because of a time delay between when an RTP pipe is assigned to a session and when the active session count for that RTP pipe is incremented.
Although VTAM does not assign new sessions to an RTP pipe that has reached or exceeded the specified sess_lim value, the APPN node on the other end of that RTP pipe can continue to add new sessions to that RTP pipe. The node on the other end of an RTP pipe might continue adding new sessions in the following circumstances:
- The node on the other end of the RTP pipe is not a VTAM node and does not support the HPRSESLM (or equivalent) function.
- The node on the other end of the RTP pipe is a VTAM running an earlier (pre-V1R10) release of z/OS® Communications Server and does not support the HPRSESLM function.
- The node on the other end of the RTP pipe is a VTAM running z/OS Communications Server V1R10 or later but has specified a larger HPRSESLM value than this VTAM. (For best results, specify the same HPRSESLM value on all of your VTAMs.)
- The nodes on both ends of the RTP pipe are VTAMs running z/OS Communication Server V1R10 or later and have specified the same HPRSESLM value, but both nodes are adding sessions to the same RTP pipe at approximately the same time.
The HPRSESLM start option is not enforced for RTP pipes that are created for interchange node (ICN) sessions. ICN sessions (sessions that traverse both APPN and subarea portions of the SNA network through an interchange node) impose special requirements for choosing an RTP pipe that has an ICN as one or both of the endpoints. In some cases, the ICN and the partner RTP node must both choose the RTP pipe that will be used for an ICN session, but they must choose it at different times. If these two nodes do not choose the same RTP pipe for the ICN session, then the ICN session fails with sense code 0897000A when the BIND arrives at the ICN over the wrong RTP pipe. To prevent this type of problem from occurring because the two nodes involved have different sess_lim values specified, the HPRSESLM start option is not enforced for RTP pipes created for ICN sessions.
Rule: Except when HPRSESLM=DISABLED is specified, VTAM ICNs running z/OS Communications Server V1R10 or later always separate ICN session onto their own RTP pipes by using a unique network connection endpoint (NCE) when creating RTP pipes for ICN sessions. This unique ICN NCE prevents pure APPN (non-ICN) sessions from sharing the same RTP pipe as ICN sessions. In a typical mixed APPN and subarea network, there are generally many more pure APPN sessions than ICN sessions. Although VTAM does not enforce the HPRSESLM start option for ICN sessions, separating ICN sessions onto their own RTP pipes prevents ICN sessions from overloading the RTP pipes that were created for pure APPN sessions and minimizes the possibility of placing too much session traffic on RTP pipes that were created for ICN sessions.