After upgrading from a 1224str to a 1335 we have intermediate static and dropped calls. We basically brought over the 1224str config, as is, to the 1335.
The phone system is a ShoreTel system. All calls stay on the VLAN where the ShoreTel phones, ShoreTel switch and ShoreTel director are.
Thank you for asking this question in the support community.
Did anything else change in the network besides the 1224STR/1335? Based on the description, all the ADTRAN unit should be doing is acting as a Layer 2 switch. Since the unit is only acting as a switch in this application, then for symptoms such as static and dropped calls, I would recommend you check errors on the physical interfaces. If there are errors on an interface, you could try moving the cable to a different port to see if the errors follow the cable or remain with the port.
Nothing else had changed in the config.
We haven't had a dropped call or static since I disabled ip ffe and enable ip route-cache express on the vlans.@
Here is a post on the differences on FFE and Route-cache: https://supportforums.adtran.com/message/10178#10178
Please, let me know if you have any further questions. I will be happy to help in any way I can.