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Calculating DSP resources in 39xx router

I have a DSP resource exercise that I'm struggling with so I thought I'd throw it out here to see if anyone is up for the challange.

First I'll start by saying I use the DSP calculator all the time and have just tried the new one that has the G2 routers in it. From what I can tell it's inaccurate in some areas.

If I select the network module NM-HD-V2E and add two VWIC2-2MFT-T1 to this module it says it can support 96 channels (48 and 48) with the fixed/onboard DSPs. This obviously is not true based on the tech sheets which says it can support max=48. Given this I don't really have a calculator that I can use for this exercise.

Here is my configuration:

I have a 3925 with 4xVWIC2-2MFT-T1 that go into the VWIC slots

I have 2 NM-HD-V2E modules with  two VWIC2-CMFT-T1

Total of 16 PRIs

I have a PVDM3-256 plus a PVDM3-128 on the motherboard.

I'm trying to figure out how many DSP conferences I can have given the above configuration.

Assume G.711 for everything.

I know that I have a total of 384 PRI channels and enough PVDM3s for 384 Channels as well as the  3 "fix" 16 channel  DSPs on the NM module (48 x 2). So I have a total of 480 channels worth of DSPs.  I'm just not sure how all of this plays together, what can be allocated to PRIs vs conferences (given the mix of PVDM2s and 3s).

Any thoughts would be helpful.


Hello - Do you mind attaching show run and show diag?


Felipe Garrido
Cisco Employee

The PVDM2s and PVDM3s need to be in separate clock domains which means you can't share the PVDM2s to any cards in the HWIC slots. This means you should treat the T1s in the NM-HD-2VEs as separate from the other T1s.

So, the 96 (48x2) resouces on the two NM-HD-2VEs will only be used for the T1s installed on the NMs.

The remaining 8  T1s in the HWIC slots will use the PVDM3s that are installed on the mainboard.The 8 T1s will require 192 channels on the DSPs, in g711 mode, and will leave you with 192 channels to devote to conferencing.

The number of conferences will depend on the number of participants per conference.


Thanks for the response.  Just a follow-up. The NM-HDV-2VE modules each have two 2port MFT cards for a total of 4 PRIs per module. Since the module only has enough PVDM2s onboard to drive one of those cards (48 channels) can the other 2 port MFT utilize the PVDM3's on the motherboard.

Thanks again.

No, as per the PVDM3 FAQ,

Q. Can PVDM2 and PVDM3 modules coexist on the Cisco 2900 and 3900 Series platforms?

A. Yes, they can coexist as long as they are not both installed in the same domain. The motherboard PVDM slots form one domain and each SM slot forms a separate domain. The motherboard domain can contain either all PVDM2 modules or all PVDM3 modules. An SM domain can only contain PVDM2 modules housed by the NM-HDV2 carrier card. If a mix of PVDM2s and PVDM3s are detected on the motherboard slots, then the PVDM2s will be deactivated, allowing only the PVDM3s to be used actively. If PVDM2s are detected in service-module slots and PVDM3s are installed on the motherboard, then both will continue to function in their own domain and coexist.

The domain for the NM-HD-2VE can only use DSPs on the NM itself. It would not be possible to "share" the DSPs on the motherboard with those ports on the NM.


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