CTCM group devices

Red Hat Enterprise Linux 9.2 LPAR mode z/VM guest

The CTCM device driver requires two I/O subchannels for each interface, a read subchannel and a write subchannel.

The CTCM device driver requires two I/O subchannels for each interface, a read subchannel and a write subchannel (see Figure 1). The device bus-IDs that correspond to the two subchannels must be configured for control unit type 3088.

This graphic is explained in the surrounding text. — Figure 1. I/O subchannel interface

The device bus-IDs that correspond to the subchannel pair are grouped as one CTCM group device. There are no constraints on the device bus-IDs of read subchannel and write subchannel. In particular, it is possible to group non-consecutive device bus-IDs.

On the communication-peer operating system instance, read and write subchannels are reversed. That is, the write subchannel of the local interface is connected to the read subchannel of the remote interface and vice versa.

Depending on the protocol, the interfaces can be CTC interfaces or MPC interfaces. MPC interfaces are used by Communications Server for Linux® and connect to peer interfaces that run under VTAM®. For more information about Communications Server for Linux and on using MPC connections, go to www.ibm.com/software/network/commserver/linux.