Maintenance modems and power failures

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