XNS/PEX questions

[Richard Stevens]

I have some questions regarding XNS in general, and the XNS support in
the 4.3 BSD kernel on a VAX:

- What is XNS typically used for ?  I assume its mainly for connecting with
  some Xerox hardware (printers, etc.).  The reason I ask this is I recall
  about a year ago after the PS/2 came out, Ungermann Bass was moving their
  Ethernet adapter to the MicroChannel and was actually going to have
  XNS support *before* TCP/IP support, which surprised me.  Are there any
  non-Xerox-hardware applications for XNS that are common (say similar to
  FTP, TELNET, etc.) ?

- The Xerox manual states that "when a host is connected to more than
  one Ethernet, its 48-bit Ethernet address on all Ethernets is equal
  to its 48-bit host number."  How do you select your 48-bit host
  number if you have more than one Ethernet interface ??

- The "Advanced 4.3 BSD Interprocess Communication Tutorial" (Sec. 5.12)
  states that the retransmission and duplicate supression code required
  to simulate the PEX protocol is "left as an exercise for the reader".
  Has anyone actually done this ??

- This same document states that PEX does duplicate supression, yet the
  Xerox manual ("Internet Transport Protocols", XNSS 028112, Dec. 1981)
  states that PEX does *not* perform any duplicate detection.  Does the
  4.3 Tutorial imply that since you have to simulate PEX with user code
  anyway, you might as well handle the duplicate detection ??

Thanks.

	Richard Stevens
	Health Systems International, New Haven, CT
           { uunet | yale } ! hsi ! stevens