1608 Dialtone

[Avayell]

S8500/G650.
The problem appears only on 1608 devices, although 4610s are used also. From time to time the user is placing the handset off hook but hears no dialtone. After pressing the hook three or four times he hears dialtone. Even more weird is the fact that if a user comes across that problem, all the other users (1608) get no dial tone. All the latest firmwares have been installed, on the 1608s but also on the CLAN. No H.323 firewall inspection.
Has anyone come across that one?
Thanks in advance.

 

[Gielo]

Check that the UDP port range specified in the IP-Network region which serves those phones are open on the network. You have a mismatch between what is set up on the network versus what is set up on the Avaya.
This usually happens if a untrusted QoS model is used where the settings received from the Avaya is re-tagged by the data switches