I have two programs that use the IL protocol. The first program sends 1000 messages (size = 17 bytes) to other program, which only function is to receive messages (that is, a client and a server). Examing the IL source code (/sys/src/9/port/stip.c) and "THE IL PROTOCOL" (The Documents, page 321), I´m thinking that the ilrexmit function (void ilrexmit(Ilcb *ic) in the stil.c is used when a message ou ack are lost. I put a debug in this function and I can see that when the client sends a message, sometimes it enters in this function. I´m using two PCs in the same room with Ethernet. Is Why did IL lost several messages? Thanks. Franklin.