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2. SIP Protocol for VoIP

The expanded form of SIP is Session Initiation Protocol. SIP is a communication protocol (more
specifically, a signalling protocol) originally developed in 1996. It uses IP protocol that establishes,
modifies and terminates VoIP telephone calls. It provides videoconferencing service to the users, so
that a user can communicate with more than one person at a time. Other SIP applications include
streaming multimedia distribution, instant messaging and information, file transfer, fax over IP and
online games. SIP transparently supports name mapping and redirection services which support
personal mobility.

8.21 NETWORK SECURITY CONCEPTS

Network is used for sharing, messaging and collaboration of data. However, more and more network
is used for this purpose, the lesser is the security of data, either in terms of viruses or hacking and
other cyberattacks. To prevent the network from these malicious and/or unethical practices, various
strategies and choices are available that work as building blocks of network security. These include
password authentication, digital signature, challenge handshake authentication protocol, etc.
8.22 Types of Threats and Prevention

1. Viruses

Viruses are small programs that are written intentionally to damage the data and files on a system.
These programs are spread from one computer system to another which interrupts the normal
functioning of a computer. Viruses can attack any part of a computer’s software such as boot block,
operating system, system areas, files and application program macros. Viruses are most easily
spread with email attachments.
Viruses are broadly classified into three types:

(a) File Infector Viruses: Viruses that attach themselves to a program file.

(b) Boot Sector Viruses: Viruses that install themselves in boot sectors of hard drive.
(c) Macro Viruses: They infect data files and corrupt the data.

Characteristics of Viruses:

(a) Speed of a computer system becomes slower than normal.
(b) Computer system frequently hangs up.
(c) Computer restarts automatically after every few minutes.

(d) Various applications of computer do not function properly.
(e) Dialog boxes, menus and other error message windows are distorted.
Damage caused by Viruses:

(a) They corrupt file allocation table which results in corrupting the entire file system.

(b) Replication of files occurs that decreases space in hard disk.
Computer Networks
(c) They can destroy system programs and files.

(d) They can cause destruction of specific executable files and alteration in data files resulting
in reinstallation of a system.

(e) They can format specific tracks on the disks or format the entire disks.
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