There are a few key features that set TCP apart from User Datagram Protocol: Ordered data transfer - the destination host rearranges according to sequence number[2] Retransmission of lost packets - any cumulative stream not acknowledged is retransmitted[2] Error-free data transfer[13] Flow control - limits the rate a sender transfers data to guarantee reliable delivery. The receiver continually hints the sender on how much data can be received (controlled by the sliding window). When the receiving host's buffer fills, the next acknowledgment contains a 0 in the window size, to stop transfer and allow the data in the buffer to be processed.[2] Congestion control [2]