VoIP packet including IP header

Unanswered Question
May 31st, 2007


We have analog card installed in router and using G.729 codec but have confusion regarding the size of per voice channel in data network with respect to technology used. Technologies like FR, ATM and Metro Ethernet.

As of now we have found that in case of FR it takes 18kpbs, in ATM it takes 22kbps and in Metro it is 25 kbps all without CRTP enabled.

Can we have a reference document which can explain it better.



I have this problem too.
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Paolo Bevilacqua Fri, 06/01/2007 - 05:56


Different media has different overhead hence the difference. Please reference a networking book, RFCs, or the many sources on the internet to see exactly how a voice packet is built depending on the encapsulation. Note, in your example, you are probably referring to VoFR and VoATM, because if it was VoIP, the bandwidth occupation should be comparable (for FR) or bigger (for ATM) to the one used on Ethernet.

Hope this helps, please rate post if it does!

ashish.nagpal Fri, 06/01/2007 - 07:04

Hi p.bevilacqua,

I know that voice packet varies on the basis of encapsulation. As in metro ethernet frame header we have addition of 802.1q that probably increases the size of per voice channel. To be more sure, I need some releavent material to go through. I would appreciate, if you can provide those RFCs nos. or any link specific to voice packet if you have. I have made lots of search but was not productive.



ashish.nagpal Mon, 06/04/2007 - 23:16

Thanks Dave, that link is really informative. If by chance you pass though something same, with perspective of Layer 2 headers, please forward me.

Thanks again



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