dxpc

Brian Pane wrote dxpc, the Differential X Protocol Compressor, when running X applications over a modem was misery and LBX did not yet exist. The program runs in two copies: one on the machine where the applications live and one where the screen is. Clients are pointed at the local proxy, display :8 by default, and the two proxies speak their own packed format between themselves. The differential part is the method: each message is encoded as the difference from the most recent one of the same type, so window IDs, coordinates and colours that repeat cost almost nothing, and the remainder goes through ordinary compression.

Unlike LBX, neither the server nor the clients had to change, which was the whole point for anyone with a Unix box at work and a 28.8 modem at home. Traffic often dropped to a tenth, but the round trips in Xlib remained, so the experience stayed sluggish. Kevin Vigor took over maintenance around the turn of the century, and NoMachine started from dxpc's code when nxproxy was written. What made NX fast was what got added on top, not the compression.