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Home office IP phone with ISDN &804

I have been requested to create a home office setup wiht an IP phone over an ISDN connection to the Internet and VPN connection back to the LAN and Call Manager. Everything appears to work OK with the exception of voice quality which is a bit "choppy". Some improvement was made by creating a separate region and using G.729 instead of G.711 back to the LAN, but it's still not acceptable with regard to voice quality. (Even with no data traffic on the line.)

Are there any other settings which may help the voice quality and has anyone see such an implementation with high or at least acceptable voice quality levels?

Community Member

Re: Home office IP phone with ISDN &804

You will most likely need to configure QOS on the outbound Wan interface...

Quality of service techniques such as IP RTP PRIORITY, or Low latency queueing can be used to make sure voice is not delayed into the network fro a queueing perspective.

You may also try turning off VAD to eliminate first word clipping... Use the voip dial-peer command "no vad"


Community Member

Re: Home office IP phone with ISDN &804

Is it 'choppy' voice or is it 'jittery' voice? Delay cannot be guaranteed through the Internet, so LLQ and IP precedence will offer very little gain in quality. Moreover, adding VPN encryption on top of this will almost certainly add delay beyond the acceptable 120 ms, probably adding echo as well?

You need to get a guaranteed QoS or RSVP through your ISP’s network, as well as using LLQ. Have you considered IP-VPN rather than Internet –VPN, this offers point to multi point with RSVP. Try looking at BT or Cable and Wireless web site, or your local service provider.

Community Member

Re: Home office IP phone with ISDN &804

It's choppy, we've done this very successfully using a 256kbps connection from overseas and have had great results with voice quality - it's as good as, or better than through the PSTN. It's a bigger connection, sure, but with the codec we're using, I would think that the bandwidth of the connection is not the problem - we used G.711 originally, but moved to 729 which made some gains, but still have issues... Delay has not been a problem from either location. Anyway, thanks for the help...I'll keep y'all posted...

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