There is information on the available IBM interconnect gateways in
Digital's Systems and Options Catalog, and in the Network Buyer's
Guide. (What will work best depends highly on what you wish to do.)
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The simplest technique is likely to locate an IP package for the IBM
system, and use a PCI token ring or PCI Ethernet interface om the Alpha
system -- assuming the Alpha in question has a PCI bus. Most Alpha
systems ship with a NAS license, which includes a license for the DEC
TCP/IP Services package (UCX).
For 16 Mbs unshielded twisted pair under UCX:
$ mcr lancp
LANCP> set devic/speed=16/media=UTP
For 4 Mbs Shielded twisted pair under UCX:
$ mcr lancp
LANCP> set dev/speed=4/media=STP
There is help available at the LANCP> prompt.
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For an SNA channel transport, use consider the DESNB-CA DEC SNA Domain
Gateway for Channel Transport package. This is a PU type 5 SNA node,
and provides bidirection access between SNA and DECnet OSI.
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Whether or not either of the above solutions is suitable depends highly
on what you want to do...