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Calculating G.729a bandwidth consumption over Ethernet

When calculating G.728a bandwidth consumption on Ethernet, the Cisco documentation and the Bandwidth calculator http://tools.cisco.com/Support/VBC/jsp/Codec_Calc1.jsp

refer to the Ethernet overhead on each frame as being 18 Bytes of Ethernet Header and FCS Tail, which they work out to be 31.2 Kbps of Ethernet consumed per G729a RTP stream.

Other sites on the Internet say 26 Bytes (adding the 8 byte preamble) or 38 bytes (adding the 8 byte preamble and 12 Byte interframe gap).

As Ethernet line speeds are measured in bps it seems to me we should include the whole 38 byte overhead in calculations, (which gives 39.2 Kbps of Ethernet bandwidth consumed).

Any comments?

1 REPLY

Re: Calculating G.729a bandwidth consumption over Ethernet

Depends on what on the payload size, set at the Cisco.

And also on the presence of VAD...

As for me, I was measuring a G729 call on a StarOS router and it was between 24-26Kbps..

You can get also the Quintum bandwidth calculator and check it. They give you the ability to calculate based on the VAD % in a conversation.

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