Path: utzoo!attcan!uunet!husc6!mailrus!purdue!decwrl!hplabs!ucbvax!TWG.COM!kzm
From: kzm@TWG.COM (Keith McCloghrie)
Newsgroups: comp.protocols.tcp-ip.ibmpc
Subject: Re: multiplexing interfaces (was 'ethernet over pcnet')
Message-ID: <8807020104.aa01228@Louie.UDEL.EDU>
Date: 2 Jul 88 01:26:27 GMT
References: <8806302243.AA04705@vax.ftp.com>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 56

James,

If I understand correctly, the Excelan and Bridge solutions in your list
only work with their own hardware, in which case users must replace all 
the existing hardware boards in each of their PCs.  All the others that
you list are your own customers !!!  However, it is still only a small 
subset of all the available permutations of boards/technologies.  
I agree that the breakthrough will come when the likes of 3Com and 
Novell support multiplexing interfaces.  The MAC/Vector interface from 
3Com has, for some time, been promising to provide one half of this, but 
I understand it may now be slated as an integral part of LAN Manager
(which will come with its own version of TCP/IP, and a whole lot more).

However, your solution does not meet the requirement stated in Brendan's 
original message.  It is a subtle distinction, but I think it's worth 
clarifying that there are multiple different user-requirement scenarios 
here :

1) a user who has an already-installed proprietary LAN, who wants to expand 
the possible connectivity of his PCs to include hosts on a TCP/IP network.

  Here, the best solution is the one which provides the minimum
  disruption/effort/problems.  It is clear that IP-over-Netbios provides 
  less or equal disruption, without imposing any limits on connectivity.
  As stated in my previous message, this is available from several
  public domain sources, and at least one commercial vendor (us).

2) a user who is setting up a new network in order to provide his
PCs with connectivity to TCP/IP-based hosts.

  For such a user, the best solution is to ignore proprietary LANs
  and use TCP/IP exclusively (unless there is a financial advantage 
  in a proprietary LAN).  If proprietary LANs are ignored, any TCP/IP 
  package for DOS can be used.

3) a user who is setting up a new network and wants to have both the
functionality of a proprietary LAN plus connectivity to TCP/IP-based
hosts.

  This is the case where the extra complexity of a multiplexing
  interface becomes potentially worthwhile, but even so, the extra 
  complexity is not just at installation/configuration-time, but 
  there is also a greater or equal level of continuing network 
  management support because of the use of multiple protocols at 
  the link layer.

There's also the issue that some proprietary LANs consist of multiple 
segments, where the segments are tied together by, say, a Novell IPX-gateway,
rather than a MAC-level bridge.  In this case, full connectivity for TCP/IP 
across the whole multi-segment LAN, is not possible if multiplexing is done 
at the driver interface.  If/when Novell provide a multiplexing interface 
to allow multiple protocols to run on top of IPX, then this is probably the 
optimum level at which to interface (i.e. using IPX as the sub-network layer) 
if the requirements for extra functionality demand the extra complexity.

Keith.