ЁЯФм
ЁЯзм
ЁЯФн
ЁЯкР
ЁЯзк
тЖР Back to Dashboard
Font Size:

1. Introduction

A computer network is a collection of computers and other devices connected together so that they can share data, software and hardware resources. The Internet itself is the largest network of all, interconnecting billions of devices worldwide. Networks enable email, web browsing, file sharing, online banking, video conferencing and countless other services that have become part of daily life. A network exists because sharing is cheaper and more convenient than duplicating resources on every machine.

Networks are built from hardware components and software rules. The hardware includes network interface cards (NIC), cables, switches, routers and modems. The software rules, called protocols, define how devices communicate, for example how a message is formatted, addressed and checked for errors. Protocols such as TCP/IP, HTTP and FTP make it possible for devices of different makes and operating systems to exchange data reliably.

This chapter explains network advantages and types, the topologies used to connect devices, the transmission media over which signals travel, important network devices, addressing through IP addresses and MAC addresses, the layered reference models, and the protocols that operate at each layer. Network questions in the board examination include definitions, protocol-to-purpose matching, identifying topologies from diagrams, and choosing the right medium for a given scenario.

2. Advantages of Networking

Networking offers several practical benefits. Resource sharing allows multiple users to share expensive hardware such as printers, scanners and storage. Data sharing lets authorised users access files from anywhere on the network. Communication becomes fast through email, chat and video calls. Networks also provide reliability through redundant paths, and they enable centralised backup and security management so data can be protected in one place. In examinations, these advantages are often asked as one-mark definition or benefit questions.

3. Types of Networks

Networks are classified by their geographic span.

PAN   < 10 m    (Bluetooth, personal)
LAN   building  (Ethernet, Wi-Fi)
MAN   city      (cable operators, campus)
WAN   world     (Internet)

4. Network Topologies

Topology refers to the arrangement of computers and the connecting cables in a network. The main topologies are:

# A simple adjacency matrix for a mesh network of 4 nodes
nodes = ["A", "B", "C", "D"]
adjacency = [[0, 1, 1, 1],
             [1, 0, 1, 1],
             [1, 1, 0, 1],
             [1, 1, 1, 0]]
for i in range(len(nodes)):
    for j in range(len(nodes)):
        if adjacency[i][j]:
            print(nodes[i], "-", nodes[j])

5. Transmission Media

Transmission media is the physical path over which data travels between devices. It is divided into guided media (cables) and unguided media (wireless).

def choose_medium(distance, speed, budget):
    if distance > 100 and speed > 1000:
        return "Optical fibre"
    elif budget < 5000:
        return "Twisted pair"
    else:
        return "Coaxial cable"

6. Network Devices

Several hardware devices build and connect networks. Modem (modulator-demodulator) converts digital signals to analogue and back for transmission over telephone lines. Ethernet Card (NIC) provides the physical interface for a computer to join a LAN. Switch connects computers within a LAN and forwards data intelligently to the correct destination based on MAC addresses. Router connects different networks and forwards data between them based on IP addresses; home broadband routers connect the home LAN to the Internet. Repeater regenerates weak signals to extend the distance, and Gateway connects networks that use different protocols.

7. Addressing: IP and MAC

Every device on a network needs an address so that data reaches the correct destination.

ipv4 = "192.168.1.10"
octets = ipv4.split(".")
print("Octets:", octets)   # ['192', '168', '1', '10']
print("Length:", len(octets))  # 4

8. The OSI and TCP/IP Models

Communication between devices is broken into layers so that each layer handles one aspect of the process. The OSI (Open Systems Interconnection) reference model has seven layers: Physical, Data Link, Network, Transport, Session, Presentation and Application. The TCP/IP model condenses this into four layers: Network Interface (Link), Internet, Transport and Application.

Each layer serves the layer above and uses the layer below. At the sending end, data moves down the layers being wrapped in headers (encapsulation); at the receiving end, it moves up with headers removed (decapsulation). This layered design makes protocols modular and easier to design and maintain.

Layer Function Example Protocols
Application User-facing services HTTP, FTP, SMTP, DNS
Transport End-to-end delivery, error control TCP, UDP
Internet / Network Addressing and routing IP, ICMP
Link / Network Interface Physical frames, MAC addresses Ethernet, Wi-Fi

9. Protocols

A protocol is a set of rules that governs communication between devices. Key protocols include:

def describe_protocol(protocol):
    table = {
        "TCP": "reliable connection-oriented",
        "UDP": "fast connectionless",
        "HTTP": "web page transfer",
        "FTP": "file transfer",
        "SMTP": "send email",
        "DNS": "name to IP resolution",
    }
    return table.get(protocol, "unknown")

print(describe_protocol("DNS"))

Quick Revision Tables

Table 1: Network Types

Network Coverage Example
PAN Few metres Bluetooth devices
LAN Building / campus School computer lab
MAN City City cable network
WAN Country / world Internet

Table 2: Guided Media Comparison

Medium Speed Distance Cost Interference Immunity
Twisted Pair Low Short Low Low
Coaxial Medium Medium Medium Medium
Optical Fibre Very High Long High Very High

Mind Map

flowchart TD A[Computer Networks] --> B[Advantages] B --> B1[Resource sharing] B --> B2[Data sharing and communication] A --> C[Types] C --> C1[PAN LAN MAN WAN] A --> D[Topologies] D --> D1[Star Bus Ring Mesh] A --> E[Transmission Media] E --> E1[Guided: twisted, coaxial, fibre] E --> E2[Unguided: radio waves] A --> F[Network Devices] F --> F1[Modem Switch Router Repeater] A --> G[Addressing] G --> G1[IP address IPv4 IPv6] G --> G2[MAC address] A --> H[Models and Protocols] H --> H1[OSI 7 layers] H --> H2[TCP IP model] H --> H3[HTTP FTP SMTP DNS]

Important Diagrams (SVG)

Diagram 1: Star and Bus Topology

Star Topology Bus Topology Hub PC1 PC2 PC3 PC4 PC5 Hub failure stops whole network T T T PC A PC B PC C Backbone break stops whole network Golden Rule: In star, a cable fails one PC; in bus, the backbone fails the entire network.

Diagram 2: OSI vs TCP/IP Layers

OSI Model vs TCP/IP Model OSI (7 layers) TCP/IP (4 layers) 7 Application 6 Presentation 5 Session Application HTTP FTP SMTP 4 Transport Transport TCP UDP 3 Network Internet IP ICMP 2 Data Link 1 Physical Network Interface Ethernet Wi-Fi Golden Rule: Each layer serves the layer above it and uses the services of the layer below.

Common Mistakes

  1. Confusing LAN, MAN and WAN coverage: LAN is a building, MAN a city, WAN a country or the world; PAN is personal area.
  2. Saying the hub failure affects only one computer in a star: The hub (or switch) is the centre; its failure stops the entire star network.
  3. Believing optical fibre conducts electricity: Fibre carries light, giving immunity to electromagnetic interference.
  4. Confusing IP and MAC addresses: IP is logical and can change; MAC is physical, burned into the NIC, and cannot change.
  5. Stating IP as the address on the NIC: The NIC carries the MAC address; the IP is assigned to the interface.
  6. Mixing up TCP and UDP: TCP is connection-oriented and reliable; UDP is connectionless and fast with no guarantee of delivery.
  7. Treating a switch and a router as identical: A switch forwards within one LAN using MAC addresses; a router forwards between networks using IP addresses.
  8. Forgetting the ordering of OSI layers: The seven layers must be memorised in the correct order; top-to-bottom order matters in questions.

Exam Tips

  1. Memorise the OSI 7-layer order using a mnemonic and the TCP/IP 4-layer equivalent.
  2. Know each protocol's one-line purpose: HTTP (web), FTP (files), SMTP (send mail), DNS (name to IP), TCP (reliable), UDP (fast).
  3. Draw star and bus topologies and state which failure is localised to which topology.
  4. Be ready to pick a topology or medium from a scenario: e.g. fibre for long distance high speed, twisted pair for cheap short links.
  5. State the IP versions: IPv4 (32-bit, 4 octets) and IPv6 (128-bit, 16 bytes).
  6. Link protocol to layer: TCP/IP work at transport/internet; HTTP, FTP, SMTP at application.
  7. Give the role of each network device in one sentence for the definition questions.

Conclusion

Computer networks connect devices to share resources, data and communication across any distance. Their types span from personal area networks to the global Internet, and their topologies trade cost against reliability. Signals travel through guided media like twisted pair and optical fibre or through unguided radio waves, carried by devices from modems to routers. Logical IP addresses and physical MAC addresses identify every node, while layered models such as OSI and TCP/IP organise the complex process of communication into manageable functions. Protocols define the exact rules by which all this happens. Together these concepts explain how data moves from one machine to another. The next chapter examines the security aspects of networking, protecting this valuable data from the threats that travel along the same wires and waves.