User Guide

TCPView Professional
User’s Guide
3 Overview of TCP/IP
TCP/IP actually consists of three protocols: TCP (Transmission Control
Protocol), UDP (Unreliable Datagram Protocol) and IP (Internet Protocol).
UDP and TCP use IP as their foundation. This section provides a brief (and
simplified) description of TCP and UDP.
3.1 TCP
TCP offers connect-oriented, reliable communications. A TCP session is
initiated by a process allocating a TCP endpoint (object) and assigning it an
IP address and port number. The IP address of course must be one local to
the computer. Local IP addresses can be specified in three different ways:
as 0.0.0.0 •
•
•
as 127.0.0.1
or as an IP address assigned to the computer (e.g. 209.233.4.14)
A process can either explicitly specify a port number or let the TCP/IP stack
assign one for it. A process typically specifies a port number if it provides a
service that has a defined port number associated with it. For example, a web
server uses port 80 because that port number is defined as being the http
port, and internet browsers by default attempt connections to that port
number.
After assigning an address/port-pair the process can either initiate a
connection to a remote endpoint or wait for incoming connections. An attempt
to connect with a remote endpoint is called a connect request, and the
process specifies the remote endpoint's address/port-pair.
When a process waits for a connection, it listens for incoming connection
requests. In order to listen it must define connection endpoints that it can, and
if it wishes to establish a connection when a connection request arrives it
accepts the connection with another TCP endpoint. Thus, the listen endpoint
Winternals Software Page 3