I have been having intermittent issues(No response, No channel available) with Ascom I62 handset in one of our customer's network. It took me two weeks to solve the issue. I hope this will help somebody out there who is having similar issues.
-Two leased lines from two different service providers. Firewalls are Meraki MX84
-3 Meraki MS and 14 Netgear switches(being replaced by Meraki switches).
-16 Meraki MR33
-LG-Ericsson UCS 100
Data network and Voice network are segragated. SSID is tagged on voice VLAN at the APs. Qos are enabled and voice traffic is prioritised at AP level and DSCP marking is trusted on switch network. (Voice best practices are strictly followed)
All is working with this set up except intermittent SIP to SIP call failure. Message we get on the handset were "No channel available" and " No Response".
Initially thought it was due to over crowded 2.4 Ghz (2.4Ghz wasnt overcrowded at all). Used 5Ghz. Didnt make any difference. I have eliminated every single component in network one by one and tested again. Created an isolated test network in the Lab with just a switch , an AP and LG Phone system but still got the same errors. Upgraded handset's and Phone system's firmware. Changed tens of parameters on the handsets and phone system and tested again. No luck
Upgraded Meraki AP firmware to Beta 26.2 and the problem is solved.
Initial AP softwares were 25.11. Upgraded to 25.13 and tested but issues were still there.
Meraki -Ascom interop document never mentioned any issues on 25.13 but we have decided to upgrade based on Meraki support's suggestion. Previous releases had some voice issues (see release notes)