I'm trying to get our Horizon phones working reliably with our 2832. SIP ALG is disabled and Always pass inbound fragmented large packets (required for certain games and streaming) is unticked under Firewall > General setup.

The connection is Virgin Media 200Mb (8ms ping, 200Mb downstream, 20Mb upstream consistently achievable) using their Hitron router in modem only mode, fed into WAN2 on the Draytek.

With no other use of the connection, the phones are slow to pickup a call and voice quality is poor.

Any help will be very gratefully received!

Just to follow up, I've also correctly set MTU on WAN2 to a value where there's no packet fragmentation. I'm not sure whether this is relevant or not, but it hasn't made a difference.

Any ideas at all? Doesn't have to be for Horizon specifically, but just with using an external SIP system with Draytek?

Thanking you in advance.