# Q on DSP

Apr 11th, 2007

hi

i have a question on DSP simple calcultions in mind without using the cisco dsp calculation tool, for example if i want to support 12 simultaneous conference bridges with 4 participants each what is the number of dsp's required

is there any table that talks about the capacity of one dsp for Conferencing, transcoding, termination,...

thanks

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## Replies

johnnylingo Mon, 04/16/2007 - 13:03
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Check out tables 5 and 6 of this link:

http://www.cisco.com/en/US/products/ps6441/products_configuration_guide_chapter09186a0080541bf3.html#wp1003287

So for termination, each DSP can do the following:

(16) with G.711

(8) with G.729a or G.729ab

(6) with G.729 or G.729b

# of DSPs per PVDM on 2800 and 3800 series:

PVDM2-16 = 1

PVDM2-32 = 2

PVDM2-48 = 3

PVDM2-64 = 4

user-cisco Wed, 04/18/2007 - 01:49

first: i think according to the tables it is (8) with G.711 for transcoding not (16) with G.711.

second: what is meant by (8) with G.729a or G.729ab

is it if transcoding from g711 to either g729a or g729ab?

also, for (8) with G.711 the transcoding from what to what?

and in case of transcoding to pstn what the pstn codec of the call (the transcoded call codec?) is it G711?

johnnylingo Wed, 04/18/2007 - 11:35
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Right, the sample numbers I posted above are for TERMINATION, not transcoding. For transcoding, if you are going from G.711 to G.729a or G.729ab, each DSP will do 8 sessions. For G.729 and G.729b, the number is 6.

There's no such thing as transcoding to the PSTN. That's what voice termination is.

paolo bevilacqua Wed, 04/18/2007 - 14:14
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Founding Member

For a nitpick, there is companding conversion going to PSTN (transcompanding? what a word!), where g711a is used.

And rememeber - Conferencing requires a dedicated DSP chip all to itself. if you have a pvdm-16 and you use it as a conferencing DSP, that DSP is done, and you need another PVDM for any terminiation or Xcodeing needs. this is why we beg sales guys to step up from pvdm-16's to pdvm-32's often.

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