FICON CTC with shared channels

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A fully redundant any-to-any CTC configuration consists of two sets of CTC minimum configurations, each associated with a separate FICON Director. CTC communication is configured such that the definitions operate in half duplex on the FICON channels. See Figure 1. For recommendations for numbering CTC control units and devices to simplify CTC configurations, see the ESCON and FICON Channel-to-Channel Reference, SB10-7034.

Note: All shared CTC examples within a single CPC exclude an LP from communicating with itself. This exclusion is required for some subsystems (for example, XCF). Other subsystems might not have this restriction and might support an LP's communicating with itself.

This example uses a simple CTC configuration approach where the same channel path is always used for sending or receiving data and the same destination link address for a control unit number is always used. For example, System A always uses CHPID 50 on switch 01 for sending data and always uses CHPID 51 on switch 01 for receiving data. Also, all CPCs always use FCTC control unit 4010 to send data to LP1A on System A through link address C1 (CHPID 51) on System A. So a single destination link address (C1) is always associated with the same control unit number (4010).

This approach results in the FICON channels having half duplex definitions. That is, all FCTC I/O data flow is on one fiber of the FICON channel resulting in its being half duplex. To balance I/O data flow on the FICON channel in this case, put tape devices on the channels used for receive FCTC control units and put DASD devices on the channels used for send FCTC control units. For example, you would put tape devices on CHPID 51 in System A and DASD devices on CHPID 50 in System A.

this graphic displays the FICON CTC (fully redundant) — Figure 1. FICON CTC (fully redundant)

Every logical partition has eight primary and eight secondary CTC connections with every other logical partition. The primary connections use switch 01 and the secondary connections use switch 02.