OA14653: POOR HPR PERFORMANCE WHEN RTP ARB DATA IS PROCESSED OUT-OF-SEQUENCE.

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• ARB Rate requests are being presented to RTP Out-of-sequence.
  RTP interpreted the data as erratic Delay Change Sum variations,
  which led to multiple Slowdowns and rate-of-flow adjustments.
  The changes caused unwarrented delays in the flow of a subset of
  the UDP/IP traffic over the pipe.  The RTP pipe flow eventually
  recovered, but not before the bottleneck was visible.
  

Local fix

• A RTP Pathswitch will also reset the affected values for the
  Pipe.  Issue an appropriate "F NET,RTP,ID=pu-name" command.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All running with RTP/HPR connections.        *
  ****************************************************************
  * PROBLEM DESCRIPTION: Intermittent performance problems       *
  *                      experienced on RTP connection.          *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  The problem is summarized as follows:
  
  Each end of an RTP pipe has sender and receiver logic.  This
  problem is in the receiver logic of a z/OS CS RTP
  endpoint.
  
  1) An RTP pipe is established and data traffic is
     occurring.
  2) VTAM is receiving ARB rate requests, as expected, from
     the RTP partner.
  3) At some point, two ARB rate requests (correlators F and 0)
     are within six milliseconds of each other on the TCP/IP host
     over EE).  SRBs are scheduled to process each inbound unit
     of work.
  4) Due to the nature of SRBs, it is possible for ARB (0)
     rate request to reach the RTP layer before the first one
     ARB (F).  This will cause RTP to process these ARB rate
     requests out of order.
  5) When the RTP layer processes ARB (0) rate request, it
     believes the ARB rate request (F) was lost in the network.
  6) The ARB (0) rate request was processed and an ARB rate reply
     returned to the partner.
  7) Now, the RTP layer receives the ARB (F) rate request out of
     order.  Invalid logic allowed the RTP layer to process the
     ARB rate request.  It was treated as if the next 14
     sequential ARB rate requests (correlators 1 through E) were
     lost in the network (when it is really out of order).
  8) This caused RTP to roll in an enormously large delay change
     (DC) into the delay change sum (DCS).  In this case, it was
     roughly 700 milliseconds.
  9) The invalid DCS causes VTAM to respond to subequent ARB
     rate requests with slowdowns.  These slowdowns indicate to
     the partner that it must cut its sending rate.  Since the
     DCS has an invalid value, VTAM repeatedly sends slowdowns
     to the ARB rate requests. Eventually, the RTP endpoints
     backup and endpoint devices and applications timeout as a
     result.
  

Problem conclusion

• Module ISTRPCAR has been corrected to process the out of
  sequence ARB rate requests correctly.  If the received ARB rate
  request is equal to, or up to three less than, the last
  processed ARB rate request correlator, it is assumed to have
  arrived out of order and is ignored.  All other ARB rate
  requests are processed as usual.
  
  Module ISTRPCRT has been included for maintenance purposes.
  

Temporary fix

• *********
  * HIPER *
  *********
  

Comments

APAR Information

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

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

  UA23625 UA23626 UA23627 UA23628

Modules/Macros

• ISTRPCAR ISTRPCRT
  

Fix information

• Fixed component name

  VTAM V4 MVS/ESA

• Fixed component ID

  569511701

Applicable component levels

• R140 PSY UA23625

     UP06/03/02 P F603 Ž

• R150 PSY UA23626

     UP06/03/02 P F603 Ž

• R160 PSY UA23627

     UP06/03/02 P F603 Ž

• R170 PSY UA23628

     UP06/03/02 P F603 Ž

Fix is available

• Select the PTF appropriate for your component level. You will be required to sign in. Distribution on physical media is not available in all countries.