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

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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 number

    OA41078

  • Reported component name

    VTAM V4 MVS/ESA

  • Reported component ID

    569511701

  • Reported release

    1C0

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt

  • Submitted date

    2012-12-20

  • Closed date

    2013-01-07

  • Last modified date

    2013-03-04

  • 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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Document information


More support for:

z/OS family

Software version:

1C0

Operating system(s):

z/OS

Reference #:

OA41078

Modified date:

2013-03-04

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