At my company we have 10 Mitel Teleworker phones (5312 model) which are connected to the PBX (3300 series) over a pair of dedicated ADSL lines (one at each site) all the phones are behind NAT on the consumer grade netgear router.
We've recently encountered a persistent issues of the Teleworker phones dropping calls and frequently dropping to a 'Please Wait...' screen upon which they eventually reconnect and calls continue until it starts again 5-10min later.
There doesn't seem to be any pattern to the times that this fault rears its ugly head.
Steps we have taken so far to try and remedy this issue include: changing the codec to the one which uses less bandwidth, having both ADSL lines checked by engineers (both are stable and provide 3000d/600u Kbps bandwidth) and checking that there's no other traffic saturating the lines.
Any help on this fault will be greatly appreciated! I'll buy anyone who finds the final fix a pizza/beer!
The one interesting thing we've found is that in the router firewall logs there's a lot of TCP and UDP traffic being directed to the PBX which is coming from the phones on random ports, and it frequently rotates to other ports which are also unlisted in any records.
This traffic is currently getting blocked, but once I allowed it (reckoning it might of been key presses or phone traffic) once I did this the issue got MUCH worse.
Any help will be greatly appreciated! I'll buy anyone who gives a solution to this problem a pizza/beer!