DSP Calculator

Unanswered Question
Jun 14th, 2006
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Hello Everybody

I`m designing a CME with 2851 ISR Router. It has 96 IP Phones and a E1 interface to the PSTN (30 voice channels). I have a issue calculating a DSP resources. I will like to know a cisco document who talks about the DSP calculator. I`ve used the DSP Calculator tool but the issue is that it ask me about the number of transcoding and coferences... I`m not sure how many I should put there.

My scenario is: CCME 2851 with 96 IP Phones and a E1 interface to the PSTN on the central site and remote site CCME 2811 with 36 IP phones and a E1 interface to the PSTN. I will like to have cominications between these CCME, conference and conference to the PSTN. I`m going use a H323 with codec G729 to doesn`t oversubscribe the link.

Thanks in advance

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Aaron Harrison Wed, 06/21/2006 - 23:45
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Have a look at this URL to see what scenarios transcoding will be used:


You will need to estimate how many concurrent instances of conferences which include a party from over the WAN (or from the PSTN transferred over the WAN).

You will also need to estimate how many calls will come in through the PSTN at one site and be transferred to the other site.

These are two scenarios that are likely to incur additional DSP usage.

Each E1 interface if full used (30 channels) with G711 calls would require 30 channels of DSP. If a call is using G729 then it will use 2 channels of DSP (60 channels total) - your number will be somewhere in the middle...

Given your number of users, I would put a PVDM2-64 in each site - this should allow for a few analogue ports in addition to the E1 and leave a good few channels for events where G729 is used in conferences or diverted to VM.

If you know you will have a lot of intersite traffic then maybe slip some extra in..


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