DSP Usage

Unanswered Question
Mar 10th, 2010

I've got two 3845 voice gateways each configured the same.  The IOS version is 12.4(13f).  In slot 0 I have 4 PVDM2-64 modules.  In slot 1 I have an NM-HDV2-2T1/E1 with 3 PVDM2-64s.  Slots 2, 3 and 4 all have NM-HDV2-2T1/E1 modules and none have any onboard PVDMs.  Hardware conferencing is configured.

I have 2 questions:

1) Is it possible to share the DSPs from some of the other boards so I can use Slots 2, 3, and 4 without having to physically move the PVDMs?  If I put "dspfarm" under voice-card 3, I can get signaling, but no audio.  Phone rings, caller ID shows up, but you can't hear anything in either direction.  I set up another ISR directly connected with a T1 crossover and got the same result, so it's not an issue with ACLs.

2) If I have 3,000 phones that will be using these ports to connect to the PSTN.  Is it likely that I'll need more PVDMs anyway?  Remember there are 2 VGWs here so the load for each router is divided in half.  I've had conflicting answers to this question.  Is there a good rule of thumb?  A web link with a definitive answer?

I've attached what I think are important configs, but the basic issue is what's described above.

Thanks.

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Paolo Bevilacqua Wed, 03/10/2010 - 13:09

Sharing seems a complicated design.

Why don't you take the easy route and get 3945 with 4 x PVDM3-256.

That should be enough for the foreseable future.

refram Tue, 03/16/2010 - 16:11

I was able to get this myself.  First of all, the magic phrase to search on is "DSP Sharing".  The best document I found was:

http://www.cisco.com/en/US/docs/ios/12_3/vvf_c/interop/intcnf2.html#wp1087168

The basic idea follows:

1) Do a “network-clock-participate” for all of the devices that have to participate in the sharing.  This includes the devices that were sharing their DSPs plus the devices that want to use them.
2) Do a “dspfarm” on all of the voice-cards that are participating in the share as well.

So because the DSPs to be shared are on the motherboard, and because I wanted to get the devices in slots 2 to use those DSPs, I issue:
network-clock-participate slot 2
network-clock-participate wic 0


Then on the voice-cards:
voice-card 0
dspfarm
!
voice-card 2
dspfarm

David Hailey Tue, 03/16/2010 - 16:59

Just to confirm - Refram is dead on with his answer.

Hailey

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