Craddock, Chris wrote: [snip]
TCP goes over XCF inside the plex.
TCP traffic *can* go over XCF in a sysplex (it's optional.) So can SNA traffic (also optional). Basically, CS knows about XCF and will move traffic that way if you allow it to do so. Very slick!
And (my favorite part) it's really good for maintaining member state data and driving exits to tell me when other members disappear. Without that sort of functionality I'd be up to my armpits in protocol code that I really don't want to have to deal with.
You said it, bro! Using a point-to-point protocol among 'n' application members, each member must maintain 'n-1' sessions with its peers. That can get pretty hairy! E.g., an 8-way plex with just one application member per system requires 56 total sessions! XCF solves that by providing a "shared medium" type of protocol, similar to that provided by a LAN, where each member is responsible for managing a single connection only. State information about other members is maintained in a "peers" table which can be updated by incremental changes surfaced via the group exit or built from scratch or as needed by a simple query.
XCF is a _very_ nice protocol. It's difficult to understand why any developer of authorized/privileged code would choose an alternative message delivery protocol unless their design called for spanning sysplex boundaries or had code in common with a non-z/OS system. In particular, SDSF's MQ choice does not appear to have been made by technicians, especially in light of the fact that MQ is a fairly expensive cost option. In the words of the immortal Yogi Berra, "It's too coincidental to be a coincidence!"
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