Question

Imagine that a two-way handshake rather than a three-way handshake were used to set up a connection. In other words, the third message is not required. Are deadlocks now possible? Give an example or show that none exists

Answer 1

Deadlocks are possible. For example, a packet arrives at A out of the blue, and A acknowledges it. The acknowledgement gets lost, but A is now open while B knows nothing at all about what has happened. Now the same thing happens to B, and both are open, but expecting different sequence numbers. Timeouts have to be introduced to avoid the deadlocks.