Re: PM3

Marty Likier (marty@livingston.com)
Sun, 24 Nov 1996 08:22:30 -0800 (PST)

>> Yes. Busy-out can be accomplished manually or each DSP can make itself
>> busy-out, if it fails an automatic self test. The auto self test is run at
>> initial power up, and after the termination of every call.
>
>Hi Marty, is the manual-busy going to be part of the DSP's function, or
>part of the chassis's function? I'm asking because it's important that
>lines get busied out especially if the DSP is so badly hooped (ie all the
>blue smoke got let out) that it has ceased to recognize that it even
>exists.
>
>I'm assuming this is a function of the chassis, as something has to busy
>out the lines when a modem card is yanked out.
>
>Confirmation?
>

You can think of it as chassis controlled, but we don't busy-out the phone
line we busy-out the DSP (modem). In essence, we remove the bad modem from
the available modem pool. In the PM3 design, all modem DSPs are connected to
2 high speed TDM buses. The 2 TDM buses are connected to a TDM switch. On
one side of the TDM switch terminates the 2 TDMs where all modem DSPs
reside. On the other side of the switch, are two TDM buses, one for each
incoming PRIs line (don't take me too literal in my description on the PRI
side - there is really a little more detail I'm omiting). But in any event,
any incoming call from either PRI line, can be switched to any of the
available DSPs. This really makes efficient use of the modems installed in
each chassis. Because any modem is available to any incoming caller.

By not busying-out the phone line, just the DSP, a couple things happen. One
the incoming line can still be used for ISDN calls. Two, in the event that
you have extra modems installed, the extra modems become hot standby spares
without any operater intervention. Meaning, lets say you have a one PRI
chassis filled with 3 x 8 modem cards. That a total of 24 available modems
in the PM3. But because PRI service only delivers 23B + 1D, you actually
have one extra modem available in the pool. So if you busy out one modem,
the extra modem automatically takes its place, so you can still process 23
concurrent modem calls, even though you took one modem DSP out of service.
BTW, you can populate up to 60 modems in each PM3 chassis, in almost any
even combination from 8 to 60 modems. So if you determine adding extra
modems is a good idea, you can pretty much pick the number of extras you
deem adequate.

I hope I wasn't too long winded. ;-)
--Marty

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