Page 84 - Intelligent Communication Systems

CHAPTER 7/NEWLY DEVELOPED TELECOMMUNICATION SERVICES 67

FIGURE 7.1 I TCP/IP protocol example.

7.7 INTRANET

An in-house equivalent of the Internet is called an intranet. Intranets can be con-
nected to the Internet to give a user access to resources such as files or databases
on the Internet, On the other hand, this means that the company's confidential
information may be accessed from outside, via the Internet. To protect such con-
fidential information, a firewall is constructed. Information that is not confidential
can be accessed from outside. An example of an intranet is shown in Figure 7.12.
Both the Internet and an intranet are local area networks interconnected by routers
or gateways.

7.7.1 Firewalls

A firewall is used to protect an intranet from the attacks of hackers or dishonest
users. If there is no firewall at the entrance of an intranet, anyone may enter it and
steal secret or private information. A firewall is a system to protect information.
The firewall can be installed at various points of the intranet. It can be installed
between LANs to protect the information of a department or section of the com-
pany. It can provide not only filtering but also encryption, authentication, and virus
detection.
A basic function of a firewall is DP filtering. Because an IP address is used for
routing of TCP/IP, the IP address is used to check a source and a destination. The
firewall knows which application is used by checking a port number. By means of
a three-way handshake, it knows which is the source and which the destination.