There are about 20 computers on the network that all access a remote terminal server using RDP. This remote TS hosts all the applications and data that the business needs to function. Local computer use is negligible; perhaps some web surfing at lunchtimes, but nothing else except redirected print jobs from the TS going to the local printers.
The business also has a VoIP telephone system on a separate network, with its own internet connection. The phones have been no trouble apart from one glitch which was an issue at the remote server end.
There are two BT Infinity 80Mbit fibre connections on site, one for the TS connection and the other for the phones. Both connections run quite close to what it says on the tin - 74Mbit down and 18Mbit up, according to Ookla's speedtest and BT's own tool.
Here's the problem:
Performance on the hosted platfom is dire, alternating between bad and very bad. There is frequently noticeable lag when typing, but it can get as bad as 10-15 seconds between keypresses and characters appearing on screen. Anything involving moving images is basically unwatchable because it's so jerky, and the audio is almost invariably out of sync. TS sessions often drop, though they usually reconnect fairly quickly. However, it has to be said that every so often things will run smoothly for a few minutes, but then it's business as usual again. Whenever things on the hosted platform are running badly, local internet access is unimpaired.
I've tried swapping the internet connections, and swapping routers, with no improvement. Likewise, enabling and disabling QoS had no effect. The routers being used are a Cyberoam CR25ia and a Draytek 2860, configured so that the computer and phone LANs and WANs are isolated from each other. Having everything on the same LAN with load balancing of the WAN connections was also tried, but that just made the TS sessions even more unreliable. The lines have been tested by BT and no faults have been found.
The hosted platform provider is adamant that it's a local problem, but I'm not convinced, particularly in view of the fact that local internet access always works well regardless of how badly the TS sessions are behaving.
I'd be very glad of input from those wiser than I...