VOIP CLipping 1

[paulos2002]

I have a VPN set up and have been configuring iPhoneManager
as a softphone at the remote end. All works fine until the call is made. From the remote end voice transmission is fine but coming back it clips so you cannot hear every other word. Has anyone come across this. The VPN is working over 1mb ADSL at both ends

Thanks

 

[Ragnorak]

ADSL is asynchronous. Typically you get a 128K or 256K upload. Your tunnel is limited by the upload at both ends, so you effectively have a 128K or 256K tunnel. If one end has a higher upload than the other, this might be your problem.

Another thing to look at is the VPN hardware/software. The encryption on the tunnel may actually be the bottleneck. You might be fine at one end because you have a better processor handling the encryption.

You could also try playing with the compression mode.

 

[paulos2002]

Thank you. I have no encryption at the moment. Once working
I will then apply the encryption. Would you use G729a?
How many frames? Silence Suppresion on? How many packets would you recommend? Fast Start on or off?
Would appreciate any advice

 

[NickBall]

Had similar problems with VPN and Softphone ...
DTMF Out of Band helped, trial and error with the compression mode, although it is now configured for G729a. Fast Start is enabled, Silence supression is on, but we do not allow Direct Media path .. Had lots of Problems with european Routing with that enabled, particulalry France to UK, UK to France.

 

[Morrack]

In north america you typically get 1.5M downstream and 640k upstream, which is a lot easier to work with.

Definately go with g.729a on adsl. Don't play with the payload size it will be set automatically based on the codec (20 for g.729 I believe). Personally I hate silence suppression but it has its uses.

How many conversations are you trying to maintain simultaneously? Also, do you at least have QoS to the edge of your two networks? Ie. do your routers support QoS?

 

[NewNic]

With Silent suppression on, you may get cliped at the front of each sentance.....