Unit 4: Networking and security
Information Technology notes · PTU syllabus (BSIT104/BSBC104)
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Unit summary
Networks connect computers and people — and bring security threats. This unit covers network types and topologies, communication devices and media, internet applications — email, Telnet, FTP, WWW and chatting — intranets and extranets, security management tools, viruses, worms and threats, and firewalls and proxy servers.
After this unit you can
- Explain network types and topologies
- Explain communication devices and media
- Explain internet applications, intranets and extranets
- Explain security threats, firewalls and proxy servers
PTU syllabus topics
- Network types and topologies
- communication devices and media
- internet applications (e-mail, TELNET, FTP, WWW, chatting)
- intranet and extranet
- security management tools
- viruses/worms/threats
- firewalls and proxy servers
Bus
All devices on one cable
Cable fault stops the network
Star
All devices to a central hub
Hub failure stops the network
Ring
Devices in a closed loop
One break can stop the ring
Mesh
Devices linked to many others
Costly cabling
Topic 1
Network types
PAN
Personal area — a few metres
Bluetooth earphones and phone
LAN
Building or campus
Computer lab network
MAN
City
Cable TV or city Wi-Fi network
WAN
Countries and continents
Internet, bank networks
Topic 2
Network topologies
Physical topology is the actual layout of cables and devices; logical topology is how data actually flows.
Bus
Cheap, little cable
A cable break stops the network
Star
Easy to add devices and find faults
Hub/switch failure stops everything
Ring
Orderly access, no collisions
One break can stop the ring
Mesh
Highly reliable, many paths
Costly cabling: n(n − 1)/2 links
Hybrid
Flexible, combines strengths
Complex to design
Example
A full mesh of 5 devices needs 5 × 4 / 2 = 10 links.
Topic 3
Communication devices
Hub
Physical
Repeats incoming data to all ports
Repeater
Physical
Regenerates weak signals
Bridge
Data link
Connects two LAN segments and filters by MAC
Switch
Data link
Sends frames only to the destination port using a MAC table
Router
Network
Forwards packets between networks using IP addresses
Gateway
All layers
Connects networks using different protocols
Basic configuration: a switch learns MAC addresses automatically; a router is configured with IP addresses on its interfaces, a default gateway and routing (static or dynamic, such as RIP or OSPF).
Exam tip
A hub creates one collision domain for all ports; a switch gives each port its own collision domain; a router separates broadcast domains.
Topic 4
Communication media
Guided (wired)
Twisted pair (Ethernet), coaxial cable, optical fibre
Unguided (wireless)
Radio waves (Wi-Fi), microwaves, infrared, satellite
- Optical fibre: highest bandwidth, immune to electromagnetic interference — backbone of the internet (BharatNet).
Topic 5
Internet applications
- Email: sending messages with attachments (SMTP to send, POP3 or IMAP to receive).
- Telnet: remote login to another computer (insecure; replaced by SSH).
- FTP: transferring files between computers (SFTP for secure transfer).
- WWW: linked web pages accessed by browsers using HTTP or HTTPS and URLs.
- Chatting and messaging: instant messaging, video calls (WhatsApp, Teams, Zoom).
Topic 6
Intranet and extranet
- E-business is broader than e-commerce: it uses internet technologies for all business processes — procurement, production, HR, collaboration and customer service — not just buying and selling.
Internet
Public — anyone
Global network for websites, email, e-commerce
Intranet
Employees only
Private network for HR policies, internal portals, collaboration
Extranet
Selected outsiders — suppliers, dealers, partners
Secure partner access to orders, inventory, specifications
Topic 7
Security management tools
- Antivirus and anti-malware software, firewalls, intrusion detection systems, strong passwords and multi-factor authentication, encryption, regular updates and patches, backups, access control.
Topic 8
Viruses, worms and other threats
Virus
Attaches to files and spreads when they run
Worm
Self-replicates across networks without a host file
Trojan horse
Disguised as useful software
Ransomware
Encrypts data and demands payment
Spyware and adware
Steal information or show ads
Phishing
Fake emails or sites stealing credentials
- Prevention: do not open unknown attachments, download from trusted sources, keep software updated, use antivirus, back up data.
Topic 9
Firewalls and proxy servers
- Firewall: hardware or software that filters network traffic according to security rules — blocks unauthorised access.
- Proxy server: an intermediary between users and the internet — forwards requests, hides internal addresses, caches pages to speed access, filters content.
Main role
Block or allow traffic by rules
Act on behalf of clients for web requests
Works at
Network and transport layers mostly
Application layer
Extra benefits
Protects the whole network
Caching, anonymity, content filtering
Key terms
- LAN
- Network covering a small area
- Topology
- Physical or logical arrangement of a network
- FTP
- Protocol for file transfer
- Worm
- Self-replicating malware spreading over networks
- Proxy server
- Intermediary server for client requests
Quick revision
- PAN, LAN, MAN, WAN.
- Bus, star, ring, mesh, tree, hybrid topologies.
- Hub, switch, router, modem, gateway, repeater, bridge; guided and unguided media.
- Email, Telnet, FTP, WWW, chat; intranet and extranet.
- Security tools; virus, worm, Trojan, ransomware, phishing; firewall vs proxy.
Important exam questions
Practice questions written to the PTU exam pattern for this unit's syllabus: short answers (Section A style) and long answers (Sections B and C style).
Short-answer questions
- Q1.Distinguish LAN and WAN.
- Q2.Name four network topologies.
- Q3.Distinguish a hub and a switch.
- Q4.What is FTP used for?
- Q5.Distinguish a virus and a worm.
- Q6.What is a proxy server?
Long-answer questions
- Q1.Explain network types and topologies.
- Q2.Explain communication devices and media.
- Q3.Explain internet applications and intranet and extranet.
- Q4.Explain security threats and the role of firewalls and proxy servers.
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