Introduction to Computer Networks
1. Definition
A computer network is an interconnection of two or more autonomous computers (nodes) through communication links and hardware (cables, switches, routers, wireless access points) so that they can exchange data and share resources according to agreed rules called protocols. "Autonomous" is the key word — a mainframe with dumb terminals is not a network, because the terminals cannot work on their own.
2. Basic Terminology
| Term | Meaning |
|---|---|
| Node / host / station | Any device attached to the network (PC, phone, printer, server, IoT sensor) |
| Link | The communication channel between two nodes (cable, fibre, radio) |
| Bandwidth | Maximum data rate a link can carry (bits per second) |
| Throughput | Actual data rate achieved (always ≤ bandwidth) |
| Latency (delay) | Time for a bit to travel from source to destination |
| Jitter | Variation in delay — harmful for voice and video |
| Packet / frame | A block of data with headers used for addressing and control |
| Protocol | Set of rules for format, timing and meaning of messages (TCP/IP, HTTP) |
| Topology | Physical/logical arrangement of nodes (bus, star, ring, mesh) |
| Address | Unique identifier of a node (MAC address, IP address) |
| NIC | Network Interface Card that attaches a device to the medium |
3. Components of a Network
SENDER MEDIUM RECEIVER
┌──────────┐ ┌──────┐ ┌───────────────┐ ┌──────┐ ┌──────────┐
│ Computer │──►│ NIC │──►│ Switch/Router │──►│ NIC │──►│ Server │
│ + data │ │ │ │ + cable/wifi │ │ │ │ + app │
└──────────┘ └──────┘ └───────────────┘ └──────┘ └──────────┘
▲ protocol / software stack (TCP/IP) ▲
└──────────── message, address, error control ───────────┘
- Sender/receiver devices — end systems that produce and consume data.
- Transmission medium — guided (twisted pair, coax, fibre) or unguided (radio, microwave, infrared).
- Interconnecting devices — NICs, hubs, switches, routers, gateways, modems, access points.
- Protocols and software — the layered rules that make heterogeneous machines understand each other.
- Network services — DNS, DHCP, e-mail servers, web servers, file servers, firewalls.
4. Classification of Networks
(a) By scale / coverage
| Type | Full form | Span | Example |
|---|---|---|---|
| PAN | Personal Area Network | A few metres | Bluetooth headset, smart watch |
| LAN | Local Area Network | A room, building or campus (up to ~1 km) | Office Ethernet/Wi-Fi, college lab |
| CAN | Campus Area Network | Several buildings | University campus backbone |
| MAN | Metropolitan Area Network | A city (5-50 km) | Cable TV network, city-wide Wi-Fi, metro Ethernet |
| WAN | Wide Area Network | Country/continent/global | Internet, bank branch network, MPLS links |
(b) By topology — bus, star, ring, mesh, tree/hierarchical, hybrid.
(c) By transmission technology — broadcast (one shared channel, e.g. old Ethernet, Wi-Fi radio) and point-to-point (dedicated link between exactly two devices).
(d) By switching technique — circuit switching (dedicated path, telephony), message switching, packet switching (the Internet).
(e) By relationship — client-server (central server provides services) and peer-to-peer (all nodes are equal).
(f) By ownership/access — private (intranet) vs public (Internet); wired vs wireless.
5. Goals and Uses of Networking
- Resource sharing — printers, scanners, storage, GPU servers, software licences, databases.
- Data and information sharing — one source of truth for records and files.
- Communication — e-mail, chat, VoIP, video conferencing, file transfer.
- Centralised management — updates, backups and policies applied from one place.
- Cost effectiveness — many cheap PCs instead of one expensive mainframe.
- Reliability and availability — replicated data and alternative paths keep service running.
- Scalability — add nodes as demand grows.
- Remote access and mobility — work from anywhere through VPN and the cloud.
- Enabling applications — e-commerce, e-governance, UPI banking, e-learning, telemedicine, streaming, online gaming, IoT and smart-city services.
6. Drawbacks and Risks
Initial hardware/software cost · recurring bandwidth and maintenance cost · need for skilled administrators · security threats (malware, hacking, ransomware, data theft) · viruses spread faster · risk of privacy loss and data leakage · dependence on the network (an outage halts work) · a badly designed central server can become a single point of failure · legal/regulatory compliance requirements.
7. Exam Points
- Define a computer network. List its components — 5 marks, very frequent.
- List any six advantages and two disadvantages of networking — 5 marks, almost certain.
- Classify networks by scale (PAN, LAN, MAN, WAN) with range and one example each — 5 marks, frequent.
- Differentiate client-server and peer-to-peer networks — 5 marks.
- Explain broadcast vs point-to-point and circuit vs packet switching — 3-5 marks.
- Define bandwidth, throughput, latency and jitter — 3-5 marks.
- Write short notes on the applications of computer networks — 5 marks.