Unit 6: Data Communication and Computer Network

Introduction

Data communication is the process of exchanging data between two or more devices through a transmission medium such as a cable, fiber, or radio wave. A computer network is a group of computers connected so they can share resources and communicate.

Without networks, there would be no internet, email, file sharing, or cloud services.

Importance of communication and networking

• Resource sharing — share printers, files, and databases.
• Communication — email, chat, video calls.
• Centralised data — one place to access shared information.
• Cost saving — share expensive equipment.
• Collaboration — multiple people work on the same project.
• Access to global services — internet, banking, e-commerce.

Data communication media

The path that carries the data is the medium. It can be wired or wireless.

Wired (guided) media

• Twisted pair cable — pairs of insulated copper wires; used in Ethernet (Cat 5e, Cat 6).
• Coaxial cable — central copper conductor wrapped in shielding; used in cable TV.
• Fiber optic cable — pulses of light through glass; very fast, used in long-distance and backbone networks.

Wireless (unguided) media

• Radio waves — Wi-Fi, AM/FM, mobile networks.
• Microwaves — point-to-point links, mobile cell towers.
• Infrared — TV remotes, short distance.
• Satellite — global coverage, used for rural internet (Starlink, VSAT).

Data transmission across media

Data can be transmitted in three modes:

Mode	Direction	Example
Simplex	One way only	TV broadcast
Half-duplex	Both ways, one at a time	Walkie-talkie
Full-duplex	Both ways at the same time	Telephone

There are also two main transmission types:

• Analog transmission — continuous signals (voice on a landline).
• Digital transmission — discrete 0s and 1s (computer communication).

Data transmission and data networking

Networking allows many devices to send and receive data simultaneously. Two main switching techniques are used:

• Circuit switching — a dedicated path is set up for the entire conversation (traditional phone calls).
• Packet switching — data is split into packets that take any available route (internet).

Computer network

A computer network is a collection of devices (nodes) connected so they can share data and resources.

Network types

Based on geographical area:

Type	Area covered	Example
PAN	Personal, a few meters	Bluetooth devices
LAN	Local, building / office	Office Ethernet/Wi-Fi
MAN	Metropolitan, a city	Cable TV networks
WAN	Wide, across cities/countries	Internet
CAN	Campus, university campus	College campus network
GAN	Global, world wide	Internet, satellite nets

Network topology

The topology is the physical or logical arrangement of devices in a network.

• Bus — all devices share one main cable.
• Star — every device connects to a central switch or hub.
• Ring — devices form a closed loop.
• Mesh — every device connects to many others (used in WANs, IoT).
• Tree — hierarchical, mix of bus and star.
• Hybrid — mix of multiple topologies.

Star:                Ring:               Mesh:
   A                  A — B               A ─ B
   |                  |   |               │ X │
B — Hub — C           D — C               D ─ C
   |
   D

Communication protocol

A protocol is a set of rules that devices follow to communicate. Common protocols:

• TCP/IP — the foundation of the internet.
• HTTP / HTTPS — web traffic.
• FTP — file transfer.
• SMTP, IMAP, POP3 — email.
• DNS — domain name resolution.
• DHCP — automatic IP assignment.
• SSH — secure remote access.

Networking hardware

Devices commonly used in a network:

• NIC (Network Interface Card) — connects a computer to the network.
• Hub — broadcasts data to all ports (outdated).
• Switch — sends data only to the intended device (smart).
• Router — connects different networks and selects the best path.
• Modem — converts between digital and analog signals.
• Access Point (AP) — wireless extension of a wired network.
• Repeater — boosts signal strength for longer distance.
• Bridge — connects two LAN segments.
• Gateway — connects networks using different protocols.
• Firewall — filters incoming and outgoing traffic for security.

Wireless networking

Wireless networks let devices connect without cables.

Types

• Wi-Fi (IEEE 802.11) — most common LAN technology in homes and offices.
• Bluetooth — short-range, low-power (headphones, smartwatches).
• Zigbee, Z-Wave — IoT and home automation.
• Cellular (4G, 5G) — mobile internet.
• Satellite (Starlink, VSAT) — rural and remote internet.

Advantages

• Mobility — devices can move freely.
• Easy installation — no cables required.
• Scalable — add devices easily.

Disadvantages

• Slower than wired in many cases.
• Security risks — signals travel through the air.
• Interference from other wireless signals or walls.
• Range limitations depending on technology.