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Bandwith requirements VOIP, H323, Codec G.927 and Frame relay

HI,

I am calculating the amount of bandwith that I have to reserve (QoS) on my WAN in order to support VOIP using the codec G.729 and H323. My WAN is built using Frame-Relay and since my CIR is 512 Kbps I will be using cRTP. Also note that I am using a PBX solution from Ericsson not Cisco, only my network components are from Cisco.

My calculation show me that I will need 12 Kpbs for each voice channel (please correct me if I am wrong). Now my question is how much bandwidth do I have to reserve for call control (signaling)

Regards,

Screech

1 ACCEPTED SOLUTION

Accepted Solutions
Bronze

Re: Bandwith requirements VOIP, H323, Codec G.927 and Frame rela

Here is the calculation you want to use:

20 - G729 byte payload

4 - layer 2 FR overhead

2 - compressed IP/RTP/UDP header

_

26 bytes * 8 (to get into bits) - 208

20ms sampling rate - 50 packets per second so 50 * 208 = 10400 bits per G729 call. If you're expecting 5 calls over the WAN, give the RTP priority queue 52k

Signaling:

2k, minimum allowed is 8k, so give it 8k for signaling.

2 REPLIES

Re: Bandwith requirements VOIP, H323, Codec G.927 and Frame rela

Call Control is much less predictable, at least in terms on maximum bandwidth required, than the voice traffic itself. However, the bulk of the traffic, the H.245 and H.225, is transmitted before the voice path is setup. And it is safe to say that the setup traffic should be less bandwidth intensive than the voice traffic itself.

However, in band control during the call is over and above the bandwidth required by the voice. This call control is handled by RTCP (Real Time Control Protocol) and the specification states that this should never take more than 5% of the bandwidth used by the RTP stream. So in this case, 3 Kbps/call would seem sufficient to me.

Bronze

Re: Bandwith requirements VOIP, H323, Codec G.927 and Frame rela

Here is the calculation you want to use:

20 - G729 byte payload

4 - layer 2 FR overhead

2 - compressed IP/RTP/UDP header

_

26 bytes * 8 (to get into bits) - 208

20ms sampling rate - 50 packets per second so 50 * 208 = 10400 bits per G729 call. If you're expecting 5 calls over the WAN, give the RTP priority queue 52k

Signaling:

2k, minimum allowed is 8k, so give it 8k for signaling.

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