Dimensioning Router because transcoding issues.

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May 21st, 2010
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I want to deploy the following scenario:

My Telephony Service Provider give me a Digital E1 (30-channels PCM) on Main Site and I want to receive them with a router and VWIC-1MFT-E1 to transmit via ethernet to another site with other router with VWIC-1MFT-E1 to connect with one PBX. I am going to use G.729 codec in ethernet media to reduce bandwidth. I am a little confuse of I must take care about transcoding issues for router's dimensioning.

Thanks in advance for any help and tips.

Daniel Toro

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Giuseppe Larosa Mon, 05/24/2010 - 12:06
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Hello Daniel,

if you would use G.711 codec on the voip dial peer to the othe router you wouldn't need to transcode.

Transcoding is the operation of converting in real time between one codec and another and requires additional DSP resources.

You will find out that it is easier to use G.711 for your application instead of adding DSPs to the router.

in adding DSP resources for transcoding you should take in account possible 30 B channels to be converted at the same time

for example you would need a PVDM2-32

(2 DSPs) to handle 32 real time transcoding sessions

depending on your routers you may be able to install these additional modules or not

But again using G.711 is to be preferred for this application

Hope to help


danieltoro Mon, 05/24/2010 - 13:35
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Hello Giuseppe. Thank you very much for your help.

The critical problem is that the transport medium for voice traffic will be satellite link and how you understand that is a very expensive medium reason for what I require as much as possible reduce bandwidth.

In fact, my question would be: Could be solved by just putting a higher compression codec on dial-peer to other router?

What do you think?

Thanks again.



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