gtpm3m12 | Multi-Processor Interconnect Facility Reference |
An ESCON channel-to-channel (CTC) channel is a channel that has the CTC adapter function implemented in its Licensed Internal Code (LIC). An ESCON CTC channel can be logically divided into two sections:
The channel section performs the regular channel functions.
The CTC control unit section synchronizes the operations performed between two channels.
See ESA/390 ESCON Channel-to-Channel Adapter for more information. The ESCON CTC channel acts like a control unit, not a channel, on the ESCON I/O interface to the connected CNC channels. A CTC connection requires an ESCON CTC channel at one end of the connection and an ESCON CNC channel at the other end of the connection. An ESCON CNC channel is an ESCON channel that can communicate with any ESCON control unit. An ESCON CTC channel is an ESCON channel that can only communicate with a CNC channel. A CTC channel and a CNC channel in a CTC connection can send information to each other. See Figure 8 for an example of the channel structure.
Figure 8. ESCON CTC Channel Structure
The ESCON CTC channel also provides a link between the local system and multiple remote systems through the use of an ESCON Director. When attached to an ESCON Director, the CTC channel establishes a link with any other ESCON CNC channels attached to the same ESCON Director. A link requires a CTC channel at one end and a CNC channel at the other end. The local system's CTC channel does not provide a direct connection between the two remote systems.
Figure 9 shows a diagram of a 3-way ESCON configuration. The diagram illustrates the following 3 connections: