Reliable Communication Layers

To build a reliable communication layer, we need some new mechanisms and techniques to handle packet loss. Let us consider a simple example in which a client is sending a message to a server over an unreliable connection. The first question we must answer: how does the sender know that the receiver has actually received the message?

Acknowledgment (ack)

The technique that we will use is known as an acknowledgment, or ack for short. The idea is simple: the sender sends a message to the receiver; the receiver then sends a short message back to acknowledge its receipt. The figure below depicts the process.