PI67843: TCP THROUGHPUT DEGRADED OVER NETWORK WITH PACKET LOSS AND SELECTIVE ACK (SACK) ENABLED.

Obtain the fix for this APAR.

APAR status

• Closed as unreproducible in next release.

Error description

• Selective ACK (SACK) can be enabled for network connections
  experiencing packet loss. In these cases, SACK can optimize
  Duplicate
  ACK processing and improve performance. In some cases, SACK has
  a detrimental effect on the throughput.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * All users of the IBM Communications Server for z/OS Version  *
  * 2 Release 1 and 2 IP: Selective Acknowledgment (SACK)        *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * With SACK enabled during FRR, throughput dropped for a       *
  * streaming (bulk) tcp connections.                            *
  ****************************************************************
  * RECOMMENDATION:                                              *
  * Apply the PTF.                                               *
  ****************************************************************
  During FRR, SACK processing was transmitting new TCP packets one
  at a time instead of grouping them together. This increased the
  latency of a streaming (bulk) connection resulting in lower
  throughput.
  

Problem conclusion

• SACK processing was changed to send new tcp packets more
  efficiently
  

Temporary fix

Comments

APAR Information

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

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

  UI40893 UI40894

Modules/Macros

• EZBTCRDF
  

Fix information

• Fixed component name

  TCP/IP V3 MVS

• Fixed component ID

  5655HAL00

Applicable component levels

• R220 PSY UI40894

     UP16/11/01 P F610

• R210 PSY UI40893

     UP16/11/01 P F610

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.