Tether

A reliable, TCP-style transport built from scratch on UDP in C, with file transfer and live chat running on top. It uses its own 12-byte packet format with a three-way handshake, a sliding window with a retransmit timer on every packet, cumulative ACKs with out-of-order reassembly, and a four-way FIN teardown. Tested end to end under packet loss, delay, reordering and duplication, using a custom UDP proxy that injects those faults.