Re: [fw-wiz] VOIP versus PBX

From: Elizabeth Zwicky (zwicky_at_greatcircle.com)
Date: 07/22/05

  • Next message: Brian Loe: "RE: [fw-wiz] Discretionary WiFi Access" 
    To: "Michael H" <af_pilot33@hotmail.com>
Date: Thu, 21 Jul 2005 16:38:44 -0700

    On Jul 21, 2005, at 1:55 PM, Michael H wrote:
    > Well here's the deal, they will also route our data traffic so we will
    > be eventually switching off our current T-1. We are also getting two
    > T-1's for some redundancy since I'm a little nervous.

    How much experience do you have with redundant T-1s and failures?

    In general, if you just buy 2 T-1s (even from different vendors, unless
    you pick the vendors VERY carefully), they will be routed across
    the exact same pieces of hardware for most of their lengths. The backhoe
    that goes through one will go through both. The switching hardware
    failure
    that kills one may well kill both. It's not uncommon for
    2 different vendors to be re-selling strands of the same cable owned
    by some third party. Even if they are in different cables, they will
    usually be in the same conduit.

    The really interesting question, however, is "What are the odds your
    phone
    line is in that conduit, too?" Because if that answer is above 75%,
    maybe
    it doesn't matter that your redundant T-1s aren't redundant. In my
    experience,
    redundant T-1s fail together more often than T-1s and phone service, but
    probably not even by a factor of 2, if you buy the T-1s from different
    vendors
    so that the bozos dealing with the software don't cut you off. If you
    buy
    the T-1s from the same vendor, there's no interesting redundancy at all;
    they almost always fail together.

            Elizabeth Zwicky
            zwicky@greatcircle.com

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