PM43595: CSM 4K DSPACE64 ECSA SKMB GROWTH DRS RECEIVE QUEUE WINDOW SIZE

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• TCP connection that has become DRS disabled allows data to be
  queued to the receive queue that exceeds the receive buffer
  size limit.  This excessive data is backed in CSM dataspace or
  or TCPIP private and is mapped by SKMB control blocks residing
  in ECSA.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of the IBM Communications Server   *
  *                 for z/OS Version 1 Release(s) 11, 12, and    *
  *                 13 IP                                        *
  ****************************************************************
  * PROBLEM DESCRIPTION: ECSA storage growth related to SKMB     *
  *                      control blocks mapping data on the TCP  *
  *                      connection receive queue.               *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  ECSA storage growth related to SKMB control blocks mapping data
  on the TCP connection receive queue.
  
  Dynamic Right Sizing (DRS) provides for advertising a large
  receive window for inbound streaming TCP connections under
  certain conditions.  DRS will disable if the local receiving
  application is unable to consume data at the rate it arrives
  such that data waiting to be received is 4 times the receive
  buffer size.  The DRS disablement tries to gracefully reduce
  the receive window so the sending side does not have to
  retransmit packets that are in the pipe.
  An error exists in the window management such that the receive
  window will never reduce to zero while there is more than
  2 times the receive buffer size of data on the receive queue.
  If the sending side continues to present data the non-zero
  window will allow that data to cross the network and attach
  to the receive buffer.
  Each data segment that is placed on the receive queue requires
  an SKMB control block residing in ECSA to map the data.  The
  failure to set the receive window to zero allows for data to
  be queue onto the receive queue until ECSA is exhausted.
  +-------------------------------------------------------------+
  + 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

• EZBTCRD has been amended to allow the receive window to be set
  to zero when DRS is disabling on a connection.
  
  * Cross Reference between External and Internal Names
  

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:

  UK70387 UK70388 UK70389

Modules/Macros

• EZBTCRD
  

Fix information

• Fixed component name

  TCP/IP V3 MVS

• Fixed component ID

  5655HAL00

Applicable component levels

• R1B0 PSY UK70387

     UP11/09/07 P F109

• R1C0 PSY UK70388

     UP11/09/07 P F109

• R1D0 PSY UK70389

     UP11/09/07 P F109

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.