Re: T1 and distant IP networks

Charles Hedrick (
Wed, 16 Sep 87 23:59:47 EDT

We have three situations similar to what you describe, i.e. pairs of
IP networks connected by T1. We are using the following three
  - VAXes running Ultrix with the T1 line connected to DMR11's.
        Avanti T1 Mux's are used to cut down the speed, since
        no known DEC line controller can deal with speeds this
        high. This is probably the cheapest of the 3 methods,
        if you already have the VAXes, but also give the worst
        performance and has other disadvantages.
  - Cisco IP routers, using either Digilink T1-izers (boxes that
        take a vanilla 1.5Mb synchronous signal and format it
        for T1) or Avanti T1 muxes (for cases where we need
        to use the line for things other than the IP link, e.g.
        talking to 3270 cluster controllers at the other site).
        This is my preferred solution. (Of course vendors other
        than Cisco also make routers that would do this. You
        might want to talk to Proteon and U-B also.)
  - U-B bridges. These would also need either a T1-izer or
        T1 mux. These are level 2 bridges rather than level 3
        routers, which have both advantages and disadvantages.
        (They have been discussed so often that I am not about
        to repeat the discussion.) The U-B bridges have worked
        very well, but note that you must dedicate an IBM PC
        or clone to boot them. (I believe the same PC can be
        shared for booting all U-B products.) I strongly oppose
        the use of this approach if the two IP networks are
        under different administration, and if you don't have
        support staff available at both ends. Junk coming from
        the other end can sink your network.

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