Communication Methods › CTCDASD as the Initial Communication Method

CTCDASD as the Initial Communication Method

The CTCDASD initial communication method is a combination of physical control files and VCF methods.

The MIMplex can consist of sysplexed and non-sysplexed images.

A DASD control file is used as the base communication method during initialization and recovery situations. During initialization, all systems synchronize on the DASD control file. If all VCF communication requirements are met, and INITIAL=CTC is specified, then CA MIM automatically migrates from the DASD control file to the virtual control file (VCF) on the selected master system.

When VCF synchronization has completed, the VCF is passed on demand from the master system to client systems. The VCF is passed between systems using ESCON or FICON CTC devices allocated to the CA MIM address space on each system. The CTC devices to be used by CA MIM are identified on CTCPATH statements.

Conceptually, a CTC device connects an I/O address on one processor to an I/O address on another processor. VCF data that is sent from one side is received on the other side, so every transmission consists of two operations:

• An outbound write operation from one side
• An inbound read operation on the other side

Data can be transmitted in either direction over a CTC path, but it travels only in one direction at any one moment.

When using the CTCDASD communication method, it is important to remember that the DASD control file is the base communication medium. Migration to the DASD control file occurs any time a resynchronization of the MIMplex is required. If possible, CA MIM automatically migrates back to using the VCF when resynchronization completes if INITIAL=CTC.