Bandwidth requirements for Mitel phone system

[Nerdface Killah]

We've got a bunch of 5330 Mitel phones and two satellite offices across the sea.  We have a T1 so 1.5 to our satellite offices but it also carries our Internet connection and phones in our office.  We're seeing 140ms ping times through an OpenVPN server on consumer grade routers with DD-WRT upgraded firmware.  This was recommended by our phone company.  Don't shoot the messenger.  We're seeing about 70ms ping times to our other satellite locations.  The 140ms ping times is constantly seeing dropped calls, warning that low bandwidth on the lcd of his phone, dead air is how they explain it and just poor sound quality.  I've been reading some past threads and it appears that the Mitel phones are very sensitive to latency.  Is this the case even through a VPN?  Is there recommended hardware as far as routers go that should be able to handle the connections?

[Tech Electronics]

Nerdface Killah,

Well without going into too much about your network has your vendor tried to resolve the issue? If so what have they tried so far?

Thanks,

TE

[cholzhauer]

How many is a bunch?  Without shooting the messenger, you shouldn't be using consumer-grade equipment to run a business...it's consumer grade for a reason.  With that being said, and TE can correct me if I'm wrong, I think each phone call takes 64k of bandwidth, and if that's the case, you're going to fill up your T1 pretty quickly.  A VPN is only going to add overhead to your traffic; I can't comment on your specific situation as to the need of a VPN. I can think of a few fixes, in no particular order:

Put a phone system across the pond
Upgrade your connection.
Upgrade switching/routing gear.  Depending on the number of phones you have this may not be an issue, but you'll run into issues later with something.

[Tech Electronics]

Cholzhauer,

Hmm, I think you are trying to simplify that number way too much if you are talking about actual bandwidth. If they are using G.711, which they shouldn't be for remote phones, then the 64Kbps is the minimum voice payload packet size to deliver the audio for the call which is only 1/3 of the equation necessary to calculate the total packet size per second. If you want to calculate the total necessary bandwidth then you would really need to know some more information about the entire network. What they should be using is G.729 which uses a minimum of 8 Kbps to deliver the call so that when you add that into the total packet size and divide that by the packets per second necessary to deliver the codec bit rate then you would have a better idea of how much bandwidth is necessary to support audio on a healthy network.

As for the consumer grade equipment I don't really have a comment on that, but if their vendor wishes to support that product then it is up to them to make sure that it can support their customers' needs. All we can do at this point is make sure that their current configuration is as close to optimal as possible to enable their hardware to handle the load more efficiently.

Thanks,

TE