MPCDYN

Subarea MPC Dynamics support allows subarea MPC groups to support MPC dynamics. This allows subchannel read and write devices to be dynamically added and removed from the MPC group under the system operator's control using the MVS™ VARY ONLINE and VARY OFFLINE operator commands. Subarea MPC dynamics is functionally equivalent to the APPN MPC dynamics for TRLE based MPC groups (PU Type2). In addition to enabling dynamics, the MPCDYN option will also provide better subchannel utilization by balancing the workload across the entire MPC group. This workload balancing is provided by using a round-robin technique across all the active WRITE subchannels within the MPC group. The third function which the MPCDYN option controls is MPC extended retransmission support. When a write subchannel device (or channel) becomes unavailable because of channel failure, the current and previous write operations are retried over an alternate active write device. The extended retransmission support provides an improvement in MPC group reliability and availability. This support can be very beneficial in hardware configurations that deploy hardware channel extenders. Therefore, it is recommended that the MPCDYN support should be considered for use for configurations using hardware channel extenders.

MPCDYN=NO

The MPCDYN default of NO means that VTAM® will not allow subarea MPC dynamics and will not extend the MPC DLC retransmission support. Data will be retransmitted on an MPC write subchannel device only if the current write operation fails. After a write operation completes, the data is no longer eligible for retransmission.

MPCDYN=YES

If MPCDYN=YES is coded on an MPC group statement, VTAM will enable subarea MPC dynamics for this MPC group and extend the MPC DLC retransmission capability for a longer period of time. Outbound data will be preserved for one additional write operation. If a channel error is detected prior to the completion of the next write operation, the previous write data will be retransmitted over another active subchannel write device within the same MPC group.

Rule: The MPCDYN function must be enabled on both sides of the MPC connection at the same time. Each side of the MPC connection must have the MPCDYN parameter configured the same as the partner. If MPCDYN=YES is coded on one side of the MPC connection, the partner must also code MPCDYN=YES. If the MPCDYN function is not enabled on both hosts at the same time, incompatibilities exist which may cause the MPC connection to hang.