The 3-way handshake is necessary because TCP is layered on the unreliable datagram service provided by IP, so that these control segments can be lost, duplicated or delivered out of order.
This could lead to trouble if original or retransmitted segments
arrive while the connection is being established - the handshake
used overcomes this problem.
A TCP connection is closed using another (modified) 3-way
handshake sequence involving the use of FIN control segments. An
interesting consequence of the full-duplex nature of TCP, and the
concept of graceful close is that a TCP connection
can be half-open if one side closes the connection
and the other does not.
The tutorial for this lecture is Tutorial
#03.
[Previous Lecture] [Lecture Index] [Next Lecture]
