Re: VOIP versus PBX

[Elizabeth Zwicky <zwicky () greatcircle com>]

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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