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How much bandwidth per voice call for call control on a MLPPP link?

I need to know how much bandwidth to allow per call for call control, for LLQ QOS over a MLPPP link. In the Cisco QOS SRND 3.1 manual, on page 1-15 it describes in detail how to figure out the bandwidth for Voice traffic, but it is vague concerning Call-Signalling traffic.

At the bottom of page 1-15 it states:

"* 150bps (plus Layer 2 overhead) per phone of quaranteed bandwidth is required for voice control traffic...."

Above that statement it says:

"* Multilink PPP (MLPPP) adds 13 bytes of Layer 2 overhead."

So is the math like this?

150bps +(13bytes * 8bits)= 254bps per call for call control

Further in the SRND it always seems to refer to using 'percent' in the examples, like 'bandwidth percent 5', but I'd like to hard code the bandwidth. Also I've been told by some folks to "just use 32kbps for each voice call control and you'll be just fine."

What is true amount of bps I should use for each voice call control?

Super Bronze

Re: How much bandwidth per voice call for call control on a MLPP


'control' traffic and rtp (or media) traffic are seperate things - control refers to SCCP packets, whereas RTP is the actual voice stream.

So the two need to be considered seperately. SCCP/control traffic isn't huge, and it's size basically depends on how busy your phones are... I certainly wouldn't expect to assign 32K for each phone (although 30-ish K is a common amount to see assigned to a single G729 call for RTP traffic, this may be where the confusion is).

Really you need to start with a figure like the quoted 150bps, multiply it by the number of phones you have and allow a little for overhead - then see how if performs with your traffic load. If you need more you can assign it, if you have overprovisioned you can adjust it if you need to.


Aaron Please remember to rate helpful posts to identify useful responses, and mark 'Answered' if appropriate!

Re: How much bandwidth per voice call for call control on a MLPP

I want to ask about the H.323 gateway with 4 FXS ports. How much bandwidth require? In my case, Cisco call manager has h323 trunk to this gateway through a 512kbps line.

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