[asterisk-users] What are the reasons for VoIP echo?

[Myles Wakeham]

I have an Asterisk 1.4.2 system that has been installed for about 3 
months now in our home.  We converted all of our phones to SIP phones, 
and use two different trunk providers (BroadVoice for incoming & 
FlowRoute for outgoing).

Most of the time its working flawlessly.  But about 1/3rd of the calls 
that come into us complain of an echo and what is best described as 
latency issues.  Its not consistent though.  I was on the phone with an 
insurance company yesterday for about 1 hour and the call was perfect (I 
originated the call which used Flowroute for the SIP provider).

What seems to be a pattern here is cell phones.  When we receive a call 
from a cell phone, or from certain people on certain phone systems, they 
consistently complain of echo in the call.  Its far less regular when we 
originate the call, which suggested to me that the problem might be with 
Broadvoice.  But I'm now hearing that us calling back the party doesn't 
always solve the problem either.

We upgraded our Internet feed (we're on a cable Internet through our 
cable company, with 12mb/s down, 1.5mb/s up) and that seems to have 
helped but not solved this problem.  From what I can see, its some form 
of latency issue.  We use IPCop as a firewall for our Internet access, 
but have turned off any IDS on it so that its running fast.  I can play 
online computer games through the network with no issues at all, so I 
don't think its slowing down the traffic and if it was I'd expect this 
problem to be occurring consistently on all calls.

Are there any tweaks that I can do with Asterisk to increase the network 
performance to reduce these issues?  Have others who have experienced 
this been able to identify the issues to external VoIP SIP providers 
only, or does our system have something to do with all of this?  At the 
time of the calls coming in, IPCop is telling me that we don't have more 
than 100K/s of bandwidth in use, and according to the network bandwidth 
graphs there, even with 2 people on the phone at the same time, the 
bandwidth never seems to exceed 300K/s, so I think we have plenty of 
headroom for this.  I checked with our cable provider for issues with 
modem latency, and they couldn't detect anything.  Again, I'm not 
experiencing any lag issues with computer games, particularly those that 
are heavy in interactivity, so I don't think that is the reason.

Any suggestions as to what could be tweaked would be greatly appreciated.

Myles
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Myles Wakeham
Director of Engineering
Tech Solutions USA, Inc.
Scottsdale, Arizona  USA
http://www.techsolusa.com
Phone +1-480-451-7440