> Is there any documentation on the types of communications used
> for ADSM?

Well, the usual manuals. TCPIP, coax, SNA, PVM, mostly.

>Which one is the most efficient under which circumstances.

Depends a lot on the implementation. In most cases, the TCPIP
transport is the most expensive in terms of host cycles, but the
least expensive in support and personnel.

> What type of communication does the majority of VM/ESA r2.1 shops
> use?

More like, how much of an investment do you have in each
technology. I'd venture to guess that most university sites
prefer TCP/IP over any other method. In the business world, it's
less clear -- but it works pretty well over all the supported
media. Note that most of the microcomputer and Unix clients
_require_ TCP/IP support, so you might as well do TCP for all
your platforms and not mess with the other methods unless you
absolutely have to.

>What are the requirements for each?

For TCP/IP support, you need: VM or MVS TCPIP (host)
                              PC/TCP or IBM TCP for DOS/OS/2 (PC client)
                              MacTCP (Macintosh)
                              built-in TCP/IP for most Unix versions

I'm not as familiar with the SNA/3270 methods, so I'll let
someone else answer that one.