Maintenance modems and power failures

Sean Donelan SEAN at SDG.DRA.COM
Thu Feb 11 05:42:01 UTC 1999

tex at shrubbery.NET (Austin Schutz) writes:
>	Get two modems.
>POTS ---- Modem 0 ---- Modem 1
>            |            |
>          UPS AC       Utility AC
>	This only really makes sense if you have your terminal server
>w/ redundant power, one utility AC and the other UPS AC. 

I've had troubles with two auto-answer modems daisy chained off the
same pots line, but a good solution for some cases.

A few people asked how I currently solved the problem.  I'm using
three different methods depending on the importance of the facility.

1) Nothing, and praying the modem answers
   Obvious problems
      - You name them

2) A Digital POWERswitch, which is a cool box containing essentially
an automatic transfer switch with two AC power cords for a piece of
equipment with one AC power cord (e.g. modem, switch, hub, etc)
    Obvious problems
       - Trying to find a Compaq salesperson who will let you order one
       - A big bundle of wire stuffed into the corner of the rack
       - People get confused, and unplug the equipment from the POWERswitch,
       and plug it directly into the wall outlet.  I don't know why, but
       for some reason people look at it and think "That can't be right,"
       and zap, there goes my modem.
3) "Network monitoring systems," which is a self-built Alpha unix box,
with internal 14.4 modem (I've found them more reliable, under more
conditions than 28.8 or 33.6.  I don't need speed, I need a connection.),
8 serial ports to connect to the equipment consoles, and DC power supplies
connected to the dual A&B battery supply.  Unlike AC power cords which
people unplug at will, DC power scares enough people so they don't
touch it.
    Obvious problems
       - Not labeled by UL, FCC, or NEBS; some building engineers object
       to anything without approved labels
       - DC powered, Ok for telco, but a problem other places
       - Vendor field maintenance not available, self-built
       - More complicated systems fail more often

None are perfect, and each can fail in different interesting ways.

Now, back to your regular network operations discussions.
Sean Donelan, Data Research Associates, Inc, St. Louis, MO
  Affiliation given for identification not representation

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