PM91679: DELAYACKS ARE DONE ON TELNET CONNECTION WHEN THEY SHOULD NOT OCCUR

APAR status

• Closed as unreproducible.

Error description

• Customer is running IND$FILE to send a file from the host to the
  client. The file transfer sends data in a single PIU (OIC, Only
  In Chain). The client responds with a "Send More data". The
  Acknowledgement to this packet is delayed .2 seconds when it
  should not have been.
  
  This can occur anytime the host application sends data in a OIC
  PIU. However, it is more noticable with a file transfer because
  the transfer takes much longer to complete.
  

Local fix

• In the IND$FILE configuration, change the buffer size to where
  it is greater that the VTAM logmode setting for the RUSIZES.
  10,000 would be a fairly safe number to use. This will result
  in the PIU being Chained (i.e. First-In-Chain, Middle-In-Chain,
  ...,Last-In-Chain). When the PIU from VTAM is chained, the
  Telnet Server sets the NODELAYACK and the file transfer will go
  much faster.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of Communications Server for       *
  *                 z/OS Version 1 Release(s) 10 IP:             *
  *                 Telnet Services.                             *
  ****************************************************************
  * PROBLEM DESCRIPTION: Slow file transfer because delayacks    *
  *                      is not turned off in all cases.         *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  The problem may be summarized as follows:
  1. A connection sends large amounts of data to the client.
  2. The data arrives from VTAM without chaining.
  3. Telnet sends the data to the client, but does not tell
     TCPIP to turn on NoDelayAck for this send.
  4. TCPIP delays the ACK packet, delaying inbound data from
     the client.  This slows down the throughput.
  +-------------------------------------------------------------+
  + 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

• Telnet is changed to correctly turn on the NoDelayAck
  flag when sending data to TCPIP.
  

APAR Information

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

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

  UK96067

Modules/Macros

• EZBTTSND
  

Fix information

• Fixed component name

  TCP/IP V3 MVS

• Fixed component ID

  5655HAL00

Applicable component levels

• R1A0 PSY

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