Considerations for the communications network in DB/DC and DCCTL environments

Performance factors that affect response time can be related to NCP and network considerations or host transaction processing considerations.

• NCP and network considerations
  Review the points in the network where delays might occur and try to avoid bottlenecks. Delays can occur:

  • Within a cluster and queue for a line
  • Waiting for transmission and waiting to be polled
  • Through line errors
  • Within the NCP
  • Within VTAM®
  • Waiting for IMS to receive any macro
  • Within IMS
  • Waiting for transmission of output

  Another possible problem is that VTAM cannot easily process larger output transmissions. You should check the appropriateness of the value for the OUTBUF keyword on the TERMINAL macro statements and ETO logon descriptor.

  Input can also be delayed because IMS has no more input threads left.

• Host transaction processing considerations

  Be aware of the trade-off made between the size of VTAM I/O buffers to service the communications network and the use of auxiliary storage. IMS communication traffic might share these resources with TSO and other subsystems.

  Use the VTAM authorized path option to reduce processing of SEND and RECEIVE commands by bypassing validity checks of request parameter lists (RPLs) and I/O areas specified in the RPL. You do this by specifying VAUT=1 as a parameter on the EXEC statement for the control region.

  IMS transactions should also be specified as response mode where possible. The major benefits are that the number of transmissions and line turnarounds is decreased and that line utilization is reduced.