Need some help with an asterisk system

Hello,

Please forgive me for my bad english. i’m a french people.

I am doing a voip installation for my father company. This structure have 3 desk in france (1 to paris, 1 to lyon and another one to lille).

Paris : 30 users
Lyon : 10 users
Lille : 10 users
home worker : 1 person

All communications are done using the G729 codec, and we have allow 15 simultaneous calls from the SDSL, and 4 on each other site.

In Paris, we have an SDSL 640 Kb with the asterisk server (it’s juste an asterisk. not an trixbox, freepbx or anothers).

Lyon and Lille has an ADSL 256 Kb.

All lines are dedicated to VoIP and all network is dedicated to the VoIP system.

All remote phones (ST2030) are connected to paris using the SDSL line.

We have a lot of problems with Lille and Lyon. The quality of communications are very poor, with a lot of cuts (i don’t really know how to say that in english ‘coupures de communications et hachures’).

Remote phones are using the xten stun server to pass NAT. The register addres is the public address of Paris, and we have opened the port 5060 UDP and 10000-20000 UDP in the router.

How could I completely remove all problems on remote sites ?

I hope that someone could help me.