PQ90096: INCREASE TCP SLOW START THRESHOLD WHEN INITIAL WINDOW IS SMALL

Obtain the fix for this APAR.

APAR status

• Closed as new function.

Error description

• New Function to increase the TCP slow start threshold.  The
  current implementation uses 1/2 the initial send window size.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of the Communications Server for   *
  *                 z/OS Version 1 Release 6 IP                  *
  ****************************************************************
  * PROBLEM DESCRIPTION: New Function to increase the TCP        *
  *                      Slow Start Threshold to a minimum value *
  *                      of 64K.                                 *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  New Function APAR to increase the value of the TCP Slow Start
  Threshold to a minimum of 64K.  The ssthresh will now be set
  to the maximum of 64K or 1/2 the window size received on the
  initial SYN packet.
  +-------------------------------------------------------------+
  + Please check our Communications Server for OS/390 homepages +
  + for common networking tips and fixes.  The URL for these    +
  + homepages can be found in Informational APAR II11334.       +
  +-------------------------------------------------------------+
  

Problem conclusion

Temporary fix

Comments

• Code has been amended to set the TCP ssthresh on a connection
  to a minimum of 64K.
  

APAR Information

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

  PQ85182

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

  UQ90397

Modules/Macros

• EZBTCPCN EZBTCSYN
  

Fix information

• Fixed component name

  TCP/IP V3 MVS

• Fixed component ID

  5655HAL00

Applicable component levels

• R160 PSY UQ90397

     UP04/08/03 P F408

Fix is available

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