[frezik]

No, these are design flaws that anything over TCP/IP needs to deal with. In particular, closing the connection to indicate the end of a file transfer is really bad (what if somebody pulls an ethernet cord?)

Fix sliding window? I don't think you understand TCP. This is an optimization to TCP to prevent the need to ACK every packet. It means fewer bytes on the wire and less CPU load for TCP processing, while also maintaining a respectable degree of reliability.

TCP checksums are not sufficient for data streams of more than a few kB.