- We don't use WiFi on our PCs, but i'll can try it out (but i doubt, that the WiFi is the Prob, since another Android SIP Client does not have that big of a delay)
- I thought about encryption as well. For that reason i only enabled MAC filtering. And even when i turn off MAC filtering, the delay persists.
- Codecs are all on A-law (nothing else supportet by SIP Provider anyway)
Edit:
One thing i can think of being a source for this issue might be, that the android clients all connect via Tunnel to the PBX (3cx PBX is not hosted in-house, but on a vServer) - While using 3rd Party SIP Clients, they where all connected as normal SIP Clients with STUN...
But since all windows clients are also connected via 3CX tunnel, i don't really know if that might be the needle, i am looking for. But i'll give it a try.