dokuwiki

TCP

TCP is a connection-oriented protocol that provides the flow controls and reliable data delivery services
listed next.
TCP is a protocol for managing end-to-end connections. Since end-to-end connections may exist
across a series of point-to-point connections, they are often called virtual circuits.

TCP Three-way handshake

A TCP Three-way handshake is a method of initializing a Transmission Control Protocol (TCP) session between
two hosts on a TCP/IP network. The handshake establishes a logical connection between the hosts by
synchronizing the sending and receiving of packets and communicating TCP parameters between the hosts.

**How the TCP Three-way Handshake works**
All TCP communication is connection oriented. A TCP session must be established before the hosts in the
connection exchange data. Packets that are transferred between hosts are accounted for by assigning a
sequence number to each packet. An ACK, or acknowledgment, is sent after every packet is received. If no
ACK is received for a packet, the packet is re-sent. The three-way handshake ensures that the initial request
is acknowledged, that the data is sent, and that the data is acknowledged.

These are the three stages of a TCP three-way handshake:

• The initiating host sends a TCP packet requesting a new session. This packet contains the initiating
host’s sequence number for the connection. The packet includes information such as a set SYN
(synchronization) flag and data about the size of the window buffer on the initiating host.

• The target host sends a TCP packet with its own sequence number and an ACK of the initiating host’s
sequence number.

• The initiating host sends an ACK containing the target sequence number that it received.