@calmh I just wanted to thank you for your work on all: Support multiple device connections (fixes #141) by calmh · Pull Request #8918 · syncthing/syncthing · GitHub.
I’ve been trying to get as much out of Syncthing as I can over this one WAN link with high latency. Ultimately, I diagnosed the problem of slow transfers to packet loss (< 5%, but still impactful to a high latency connection) and recorded packets along the way. Every time a packet was lost or was reordered, TCP congestion control would slow down the connection. Switching to BBR helped a lot, given it doesn’t use packet loss for back pressure detection - but I was only able to get half of my link’s bandwidth due to the high latency. No ISP traffic shaping or throttling - just a bad hop somewhere out of my control.
With multiple connections I see double or even triple the bandwidth over the same. In my testing, this is caused by each TCP stream being independently controlled by congestion control - so when one of the links slows due to congestion control, other streams can compensate.