i have a big problem with an asterisk installation with over 30 IP Phone.
After some minutes, audio stop in both direction, call is still on, on iphone call status is "connected" but no sound ... sometimes, after 1-2 minutes audio start again.
I try everything.
Asterisk is 1.2.10 with a sangoma A500 with 2 BRI TE module, ip phone is Linksys SPA942 (about 30 units) and PSTN is 2 NT ISDN from local telco company.
I also try:
Change local switch, using a separate switch (cisco 2950T) only for voice (voip).
Change sangoma with Cisco 1751-V with VIC-2B-NT/TE
Upgrade Asterisk to 1.4.27
Upgrade IP-Phone firmware.
Disable Jitter correction on IP-Phone
try force codec (now i force using G711a to avoid transcode)
Asterisk has no error on log, i try to debug RPT but i see no problem.
I also got same problem on few installations, i'm quite sure that problem is on ip-phone because i try other phones without any problem ( in same installation i got some cordless IP siemens with no problem).