In this section, we are going to look at a basic cornerstone of network services, the socket, and see how this leads to the creation of familiar operating system tasks such as the web and e-mail servers.
First, we need to introduce the concept of well-known ports.
The concept of networked services over well-known ports was introduced to Unix by the Berkeley development on the open source operating system in the early 1980s and has formed the bedrock of almost all computing operating systems ever since. The idea is that a particular service is associated with a port number and that network packets are sent tagged with this port number.
For example, originally the file transfer protocol used port 21, SSH port 22 and sendmail port 25. Today other (additional) ports may be used for these services
One port that many readers will be familiar with is 80, this is the one used by web servers to deliver HTTP content.
Security firewalls often block specific traffic on...
