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Codecs on DSP resources


If I have a VG that has got 2 E1 ports connected to the PSTN, 30 channels each. With a PVDM2-64, i should be able to make 60 x G.711 calls right? (since I'm limited by the 2 x E1 ports)

Now, if i have a bunch of phones on the back of the VG and they are all configured to place calls with G.729a. Even though G.729a takes less bandwidth per call, the transcoding should be more processing intensive, right? So how many simultenous calls can the VG send out with a PVDM2-64?



Re: Codecs on DSP resources

The DSP Calculator is your friend:


VIP Purple

Re: Codecs on DSP resources

You can support 8 medium complexity codec (g.729) calls per DSP, so with the PVDM2-64 (4 DSPs), you could support 32 g.729 calls. Take a look at the following links. As was already mentioned, the DSP calculator is a fantastic tool.

Hope this helps. If so, please rate the post.


Community Member

Re: Codecs on DSP resources

Hi Brandon & Karzazi,

If my CCM is set all calls for G729 under Region, wouldn't it mean the VG doesn't need to do the transcoding anymore, hence the PVDM2-64 can support up to 64 G.729 calls?


Super Bronze

Re: Codecs on DSP resources


When you set the regions to G729, this basically tells the devices that they can only use calls that use that amount of bandwidth as a maximum.

If they end devices are capable of using G729, they will - if not they will require a seperate transcoder.

In your case, IP phones are capable, and the gateway is capable. If you want to have 60 simultaneous G729 calls to the gateway it will require 120 channels of DSP - so you would require 2 PVDM2-64s.

Whilst your gateway isn't 'a transcoder' in terms of what it's doing, it still has to decode the IP stream and convert it to be output to the PSTN.



Please rate helpful posts..

Aaron Please remember to rate helpful posts to identify useful responses, and mark 'Answered' if appropriate!

Re: Codecs on DSP resources

A digital port using G711 is regarded as a 'low complexity' codec, otherwise known as 'flex codec'.

The PVDM2-64 can handle 64 channels of flex codec calls.

A G729 call needs 2 times more DSP cycles than a flex codec, so a PVDM2-64 can handle 32 channels of G729.

Therefore you can have up to 64 calls of G711 or up to 32 channels of G729 , or a combination of both these codecs up to the limit set by available DSP resources.

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