PSRETRY start option


   .-PSRETRY--=--(--0--,--0--,--0--,--0--,--SCHED--)--------------------------------------------------------------.   
>>-+--------------------------------------------------------------------------------------------------------------+-><
   |                .-0----------.     .-0----------.     .-0-----------.     .-0--------------.     .-SCHED-.    |   
   '-PSRETRY--=--(--+------------+--,--+------------+--,--+-------------+--,--+----------------+--,--+-------+--)-'   
                    '-low_tp_int-'     '-med_tp_int-'     '-high_tp_int-'     '-network_tp_int-'     +-IMMED-+        
                                                                                                     '-SCHED-'

range:

1 minute - 24 hours (expressed as nS, nM, or nH)

Specifies the interval between attempts to switch a rapid transport protocol (RTP) session to another path that can be equal to or better than the current path.

The following values indicate the transmission priority interval:

low_tp_int: Specifies the time interval for low transmission priority RTP connections.
med_tp_int: Specifies the time interval for medium transmission priority RTP connections.
high_tp_int: Specifies the time interval for high transmission priority RTP connections.
network_tp_int: Specifies the time interval for network transmission priority RTP connections.

You can specify different transmission priority time limits for low, medium, high, and network transmission priority connections. For example, you might want a batch connection to wait longer intervals than an interactive connection before looking for another path which may be equal to or better than the current path.

If you do not specify an S, M, or H on a transmission priority interval, seconds are assumed.

Results:

Specifying too short an interval might have a negative effect on network performance, especially if there are many RTP connections.
If you specified the PSRETRY start option, the following commands trigger path switches for all RTP sessions, regardless of the PSWEIGHT start option value:
- MODIFY procname,TGP,TGPNAME=tg_profile,ID=adjacent_node,TGN=tgn
  This command changes the TG characteristics for a TG.
- MODIFY procname,TOPO,FUNCTION=quiesce_normal,ORIG=origin_node,
  DEST=dest_node,TGN=tgn
  
  This command changes a TG from QUIESCE to NORMAL or from NORMAL to QUIESCE.
This means that RTP sessions might be switched to the same path even if PSWEIGHT is set to LESSTHAN. For information about PSWEIGHT, see PSWEIGHT start option. For more information, see the MODIFY TGP and MODIFY TOPO commands in z/OS Communications Server: SNA Operation.

Immediate path switches

Specifies whether an immediate attempt to switch RTP sessions to another path is triggered when a link on this host is activated or changes status, regardless of the specified time intervals.

SCHED: Specifies that a link activation or status change does not trigger an attempt to switch RTP sessions to another path. The path switch retry function follows the scheduled transmission priority time intervals.
IMMED: Specifies that a link activation or status change triggers an attempt to switch RTP sessions to another path.

Guideline: When using the function provided with PSRETRY, it is very important to ensure that the nodes in the network have a consistent and symmetrical view of the weights of the paths involved, as indicated with APPNCOS tables.

Results:

If the appropriate PSRETRY transmission priority interval value is nonzero, one path might be based on the PSRETRY time after an RTP pipe activates to store the path weight.
If the PSRETRY immediate function initiates a path switch, PSRETRY does not initiate any other path switches for that transmission priority until the full PSRETRY time for that transmision priority expires.
If you specify IMMED, when a link on this host is activated or changes status for more than 15 times in 24 hours, the PSRETRY IMMED function does not attempt any further path switches because of status changes to the link until the next topology garbage collection time. The topology garbage collection occurs every 24 hours. You can use the DISPLAY NET,TOPO,LIST=SUMMARY command to display the date and time of the last topology garbage collection. See the DISPLAY TOPO command in z/OS Communications Server: SNA Operation for additional information.
PSRETRY behaves differently with links that originate on a network node and connect to an end node. If you specify PSRETRY time intervals or PSRETRY IMMED on an end node, a change in a TG that originates on the end node will trigger the path switch retry function to attempt a path switch. However, if you specify PSRETRY time intervals or PSRETRY IMMED on a network node, a change in a TG that originates on the network node will not trigger the path switch retry function. This anomaly occurs because the route selection process uses only links that originate on the end node to determine the path of an RTP pipe when an end node is one of the endpoints.
Specifying IMMED prevents a link that experiences repeated INOPs from causing excessive path switches. However, PSRETRY transmission priority intervals can still trigger RTP path switches even if a link on this host is activated or changes status for more than 15 times in 24 hours.

Tip:

You can set the value PSRETRY=(0,0,0,0,SCHED) or use the default values to disable the path switch retry function.
You can set the value PSRETRY=(0,0,0,0,IMMED) to disable regularly scheduled path switch retry attempts to reduce the performance impact, but to retain the path switch retry function for a link activation or status change on this host.

You can change the PSRETRY values with the MODIFY VTAMOPTS command while VTAM® is running.