Question

Why do Transmission Control Protocol (TCP) detects packet loss and performs retransmissions to ensure reliable messaging and avoid congestion/

Answer 1

TCP is a reliable connection oriented protocol present at the transport layer.

TCP detects packet loss and performs retransmissions because TCP is a reliable protocol and it guarantees ordered delivery of packets to the destination. In case a packets gets lost, then the packets that come after the lost packet cannot be delivered to the destination until the lost packet is retransmitted and successfully received at the destination.

TCP avoids congestion in the network by changing the size of the sender's and receiver's window. TCP does not let the sender overwhelm the receiver with data that the receiver won't be able to handle. If the sender sends too much data there will be congestion in the network which increases packet loss at the routers. To avoid that, congestion control policies such as AIMD (Additive Increase Multiplicative Decrease) are employed by TCP.