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New Member

VoIP on FR issue

have VoIP installation, with 40 branches linked to head office via FR start-topology PVC links each with 64K CIR.

Each branch having 2 analog phones attaches to branch router 1751-V.

Voice trafic for each branch has given priority and has allocated 48K bandwidth for voice on each PVC.

Some branches experiencing intermittant voice quality problems.

Q1. Suppose if a branch link is having two on-going voice conversations. If a third call trie to enter the link can it cause the voice quality problem bencause the link cannot handle 3 calls ?

Q2. Will installing a voice gateway to do call admission controll at the head office will solve the problem ?


Re: VoIP on FR issue

A1. If they only have 2 phones, how can a 3rd call enter the link, it's physically not possible, and the call set up would not take up that much bandwidth.

A2. You can't get any better call admission than only having 2 phones and wanting 2 calls maximum. The possible problem maybe in the core but there isn't enough info to say that definitely.


New Member

Re: VoIP on FR issue

Yes,What you say is corect from the branch side.

But at HO there is a E1 ( 30 channel ) connectivity with the PBX. And also any other branch can call initiate call to any branch.

Unrer this config, it is possible to try for the third call while 2 calls are in progress.

Pls let me your idea on this config whether call admission controll is necessary at the HO.

Re: VoIP on FR issue

Even with this config, I can't see how it is possible.

You only have 2 ports at the branch, so if those ports are busy and attempt to set up a third would be rejected by the branch router, regardless of where the call cam from. The call set up is less than 0.5kb so there is no way this is causing the problem.


New Member

Re: VoIP on FR issue



Here aresome other ideas

That will stop the 0.5kB of call controll traversing the wan links.

If you are you using CM in the HO you would use locations for call admission controll only allowing two g.729 calls for each location /region.

If you are using a h.323 gw you could set max-con on the dial-peers to two therfor only 2 calls could be made to each location.One dial-peer for each loaction with the correct dial-plan 111X 112X 113X etc etc.

Sure it might take some time but it works.

From my eperience LLQ works well.

You could turn on cRTP and reduce the BW even more to around 12kbps or pehaps up the sampling rate to 30 or 40ms =25pkts per second around 24k with cRTP for less overhead and processing on the router though this probably isnt required their just ideas for you.

all the best.

Allan Wells