Re: set modem off effect on a PRI (was Re: (PM) Bad modem)

Mike Tancsa (mike@sentex.net)
Tue, 23 Mar 1999 23:06:06 -0500

>As I said "that's why you want 48 modems for a 2PRI unit" -- I'm well
>aware of how the PM-3 allocates modems. If you have multiple dead modems
>on a chassis, you really ought to RMA the cards. That's not a function of
>idling out the modem -- that's a function of not having enough DSPs left
>to populate your PRIs, so yes, you certainly _are_ screwed if you let
>your PM-3 lose too many modems, or if you're goofy and try to run a mixed
>ISDN/dialin chassis without a full complement of modem cards.

... Or if for whatever reason the modems go down like a software bug. We
saw this happen in earlier revs of the ComOS.

>
>Busying out a modem does not cost you a channel on your PRI, which was
>what your post that I was replying to said.

I should have been more clear. What I was getting at is what I am saying
now. If you busy out too many modems in the middle of your pool, you just
might break the rest of your span. I have seen people make the assumption
that they can safely turn off all the modems on a card thinking that it
would not have any adverse effect on the whole span.

> Having a shortage of DSPs
>can cost you channels -- and it probably means your roll sequence will
>break as well.
>
>By the way, if it wasn't just dying modems that put you there, it's not
>very wise to purchase a PM-3 in a 3x10/2x8 configuration for dialup use
>-- that leaves you with a malfunctioning PM-3 if you lose even one DSP,
>and they _do_ have a noticable failure rate (3 cards out of 40 for us).

I would never reccomend anything of the sort. Nor do I think anyone else
would. Although I am sure there are a few PM3-1s out there with only 1
modem to spare...

---Mike
**********************************************************************
Mike Tancsa, Network Admin * mike@sentex.net
Sentex Communications Corp, * http://www.sentex.net/mike
Cambridge, Ontario * 01.519.651.3400
Canada *
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