OA41078: EXCESSIVE HPR RETRANSMISSIONS DETECTED DUE TO STATUS SEGMENTS BEING SENT OUT-OF-ORDER FROM Z/OS CS

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• Excessive HPR retransmissions requested by RTP partner due
  to status segments being sent out-of-order from z/OS CS.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All using HPR/RTP connections.               *
  ****************************************************************
  * PROBLEM DESCRIPTION: Poor RTP pipe performance due to        *
  *                      excessive number of retransmissions.    *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  The problem is summarized as follows:
  1) An RTP pipe is connected to a remote partner over Enterprise
     Extender.
  2) The remote partner is receiving status segments out-of-order
     which results in the partner requesting that z/OS CS
     retransmit previously sent packets.
  3) This process is occurring repeatedly resulting in ARB rate
     reductions taking place on the z/OS side which reduces
     the allowed send rate.  This may cause RTP pipe
     performance to suffer.
  4) A problem has been found where standalone status segments
     do not pass the ISTRPN_EE_Ext (IUTRPNEE) to TCP/IP when
     the packet contains no data payload.
  5) If the ISTRPN_EE_Ext is not passed, EZBUDBYP will process
     the IUTIL request on a separate SRB, and not serialize this
     packet with other data packets sent from the same RTP pipe.
     This allows the RTP status segment to pass the data segments
     being sent and arrive out-of-order at the partner RTP.
  6) Upon receipt of the status segment, the partner RTP endpoint
     (AIX in this case) sends a status segment in response
     reporting gaps to z/OS CS.  After the gap is reported, the
     data packets arrive at the AIX side.
  7) z/OS CS retransmits packets each time AIX detects missing
     packets.  This process is occurring to a point where
     ARB rate reductions are causing poor performance due to
     excessive retransmissions.
  8) z/OS CS should not send status segments out-of-order.
  

Problem conclusion

• ISTRPNCB - Added new RPN_EE_Aging_TOD field for aging logic.
  ISTTSC89 - Changed to pass the ISTRPN_EE_Ext to the stack when
             transmitting a standalone status segment.
  ISTTSCDN - Changed to not free the ISTRPN_EE_Ext immediately.
             Instead, the control block is timestamped and queued
             to the ACM_RPNEE_Que for aging.
  ISTTSCRG - Garbage collection will not free the ISTRPN_EE_Ext
             until 15 minutes has passed since the control block
             was queued and the RPNEE_Latch is off.
  ISTRPCRT - Included for maintenance purposes.
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

  OA40864

• APAR is sysrouted TO one or more of the following:

  UA67640 UA67641

Modules/Macros

• ISTRPCRT ISTRPNCB ISTTSCDN ISTTSCRG ISTTSC89
  

Fix information

• Fixed component name

  VTAM V4 MVS/ESA

• Fixed component ID

  569511701

Applicable component levels

• R1C0 PSY UA67640

     UP13/02/20 P F302

• R1D0 PSY UA67641

     UP13/02/20 P F302

Fix is available

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