How FastAPN's TCP-split acceleration works

Most of FastAPN's speed gain on high-latency links comes from a technique called TCP splitting, and it is worth understanding what happens under the bonnet.

On a normal connection, every TCP handshake and acknowledgement has to travel the full round trip to the distant server and back. On a GEO satellite link that round trip can be over half a second, so the connection spends most of its time waiting rather than moving data.

FastAPN intercepts these high round-trip-time (RTT) connections at the network level using netfilters. It "steals" the TCP SYN packet during the three-way handshake, impersonates the destination, and then opens a separate connection onward to the real endpoint. A small userspace application copies data directly between the two sockets.

The practical effect is that your device now handshakes with a nearby FastAPN node instead of the far end, so acknowledgements return almost instantly and the TCP window opens up far faster. The slow satellite hop is handled separately, on an optimised connection tuned for that link.

Crucially this needs no changes to content servers or satellite receivers — it replaces the commercial "black-box" performance-enhancing proxies or bespoke in-house software that operators would otherwise have to install at both ends.