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Can a Cisco 1750-4v Support Four Voice Channels if G.729 Compression is Used?

What bandwidth requirement is needed across the WAN link to support these four calls?


Re: Can a Cisco 1750-4v Support Four Voice Channels if G.729 Com

The Cisco 1750 with four voice ports and packet voice data modules (PVDMs) can support four calls. In general, the

formula for calculating required bandwidth of one voice call is

[codec bandwidth _(1 + overhead/payload_size)] + 2kb additional overhead.

g729 bandwidth is 8kb/s

rtp/udp/ip headers = 12/8/20 = 40byte

defaul payload sixe of g729 is =20byte

required bandwidth = [8 * (1+40/20) ] + 2

= [8 * 3 ] + 2

= 24 + 2

= 26KB/s required per one voice call without compression

If you enable Compressed Real-Time Protocol (CRTP) Compressed Real-Time Protocol (CRTP) (for example, rtp header compression), the overhead can

be reduced from 40 to about 2 or 4 bytes and the total bandwidth for a voice call with compression would be

11.6 KB/s approx 12KB.

Therefore, for four voice calls you need 4 x 26kb/s= 104KB/s without compression

and 48kb/s with compression.

Note: Bandwidth availability does not necessarily result into good quality

voice. You will need to enable the right quality of service (QOS) to help

properly prioritize voice in a mixed data and voice network.

Visit these pages for QOS issues:


Re: Can a Cisco 1750-4v Support Four Voice Channels if G.729 Com

Depends on a few things. With g729 compression and vad turned on, you will be looking at about 24K per call. You can configure header compression which brings a lot of other things into the equation. All in all you can reduce your per call bandwidth to about 12K per call with g729. Here is a link you can look at for bandwidth consumption :

In answer to your question, depending on the PVDM's in the router, it should be able to support 4 g729 channels. G729 is a medium complexity codec.

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