LI76929: MODIFICATIONS TO RTP_TUNING TO ALLOW SMALLER REFIFO AND SRT CAPS

APAR status

• Closed as program error.

Error description

• Communications Server for AIX and Linux
  ---------------------------------------
  The define_rtp_tuning has been modified to allow for smaller
  refifo_cap and srt_cap values than documented.
  

Local fix

Problem summary

• In certain error cases the performance of an HPR/IP link can be
  poor with delays of up to half a second to receive data.
  
  Specifically if multiple frames are being lost when being
  received by Communications Server (possibly dropped by a
  router?) and Communications Server has a high internal refifo
  timer (which it computes from the round trip time or rtt) then
  it may take a long time to request retransmission of the missing
  frames, so delaying throughput. In one system the rtt was seen
  to rise to 250ms which caused the refifo timer to also be raised
  to this value.
  

Problem conclusion

• This APAR introduces two enhancements to the product:
  (1) The minimum value that the refifo_cap can be set to in
  define_rtp_tuning is reduced from 250ms to 5ms. This allows the
  large rtt values to be ignored in the protocol that requests
  retransmission. In modern fast networks it is VERY unlikely that
  packets can get delayed by more than a few ms.
  (2) Alter the default rtt timers from the architected intial
  values of 1000ms, 500ms, 250ms to 100ms, 50ms, 10ms for the
  different speed ranges. This allows HPR/IP send_rates to ramp up
  much quicker to appropriate rates for modern fast speed
  networks.
  

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:

  JR44767 LI77310 LI77311 LI77312 IV40881

Fix information

• Fixed component name

  CS LINUX ON ZSE

• Fixed component ID

  5724I3400

Applicable component levels

• R623 PSY

     UP

• R640 PSY

     UP