🔗 Computer Networks

What is a Computer Network?

A computer network is a group of two or more computers connected together to share resources like files, printers, internet, and software. When you share a document between your laptop and phone via WiFi, you're using a network.

Definition: A network is a collection of interconnected computers and devices that can communicate and share resources using a common set of rules (protocols).

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Types of Networks by Size

Network Type	Full Form	Range	Example
PAN	Personal Area Network	~10 meters	Bluetooth between phone and earbuds
LAN	Local Area Network	Within a building/campus	Office network, school computer lab
MAN	Metropolitan Area Network	Within a city	Cable TV network, city-wide WiFi
WAN	Wide Area Network	Country or worldwide	The Internet itself

LAN Features

• Covers a small area (single room, building, or campus)
• High data transfer speed (100 Mbps to 10 Gbps)
• Owned by a single organization
• Uses Ethernet cables or WiFi
• Standard PC hardware

WAN Features

• Covers large geographical areas (country, continent, globe)
• Lower speed than LAN (depends on connection)
• Uses telephone lines, fiber optic, satellites
• The Internet is the largest WAN in the world

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Network Topologies

Topology is the physical or logical arrangement of computers in a network — how they are connected to each other.

Star Topology

• All computers connect to a central hub or switch
• If one computer fails, others continue working
• If the central hub fails, entire network goes down
• Most commonly used in offices and homes

Bus Topology

• All computers connect to a single backbone cable (bus)
• Data travels in both directions along the cable
• Cheap and easy to install
• If the main cable breaks, entire network fails
• Older technology, rarely used today

Ring Topology

• Each computer connects to exactly two others, forming a circle
• Data travels in one direction around the ring
• If one computer fails, the entire network may be disrupted
• Used in some industrial settings

Mesh Topology

• Every computer connects to every other computer
• Highly reliable — if one connection fails, data takes another path
• Expensive due to many cables
• Used in military and critical systems

Tree (Hierarchical) Topology

• Combination of star and bus topologies
• Computers organized in a hierarchy like branches of a tree
• Used in large organizations with departments

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Network Devices

Device	Function
Hub	Connects multiple devices; sends data to ALL connected devices (not smart)
Switch	Like a smart hub — sends data only to the intended device (more efficient)
Router	Connects different networks (e.g., your home network to the internet); directs data using IP addresses
Bridge	Connects two LANs and filters traffic between them
Repeater	Amplifies weak signals to extend network range
Gateway	Connects two networks that use different protocols (e.g., LAN to Internet)
Modem	Modulator-Demodulator — converts digital signals to analog (and vice versa) for telephone line transmission

Key difference: Hub sends data to everyone (broadcast); Switch sends only to the destination (unicast). Switch is smarter and more efficient than Hub.

A simple hub is also called a concentrator because it concentrates multiple network connections at one central point.

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Transmission Media (Network Cables)

Wired Media

Cable Type	Description	Speed	Use
Twisted Pair (UTP)	Pairs of copper wires twisted together	10-1000 Mbps	LAN, telephone
Coaxial Cable	Central copper wire with insulation and shielding	10-100 Mbps	Cable TV, older networks
Fiber Optic	Glass/plastic fibers carrying light pulses	Up to 100 Gbps	Internet backbone, high-speed connections

Fiber optic is the fastest — uses light instead of electricity. Immune to electromagnetic interference.

Wireless Media

Type	Range	Use
WiFi	~100 meters	Home/office internet
Bluetooth	~10 meters	Short-range device pairing
Infrared	Line-of-sight, short	TV remotes
Satellite	Global	GPS, satellite TV, remote areas
Microwave	Line-of-sight, long	Point-to-point communication

Another older but important internet-access term is DSL (Digital Subscriber Line). DSL is a family of technologies used to transmit digital data over ordinary telephone lines.

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Network Protocols — Quick Reference

A protocol is a set of rules that governs how data is transmitted between devices on a network. Key protocols used in networking:

Protocol	Full Form	Purpose
TCP/IP	Transmission Control Protocol / Internet Protocol	Foundation of the internet
DHCP	Dynamic Host Configuration Protocol	Auto-assigns IP addresses
DNS	Domain Name System	Converts domain names to IP addresses
ARP	Address Resolution Protocol	Maps IP address to MAC address
ICMP	Internet Control Message Protocol	Error reporting, ping command

For detailed coverage of HTTP, HTTPS, FTP, SMTP, OSI model, TCP vs UDP, and port numbers — see the Internet & Its Protocols lesson. For email protocols (SMTP, POP3, IMAP) — see the Email & Its Protocols lesson.

In network language, each connected device is often called a node. Data is commonly broken into smaller units called packets before being sent across the network. A broadcast network is one in which a message sent on the shared channel can be received by all connected machines.

When two or more separate networks or network segments are connected together, the process is called internetworking. The resulting connected structure can be described as an internetwork, and the Internet itself is the largest real-world example of this idea.

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IP Address

An IP address (Internet Protocol address) is a unique numerical label assigned to every device on a network.

Version	Format	Example	Addresses
IPv4	4 numbers (0-255) separated by dots	192.168.1.1	~4.3 billion
IPv6	8 groups of hex numbers separated by colons	2001:0db8:85a3::8a2e	Virtually unlimited

For IP classes (A-E), NAT, subnet masks, and IPv4 vs IPv6 in depth — see the Internet & Its Protocols lesson.

IPv4 addresses are running out globally, which is why IPv6 was introduced with a much larger address space.

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Additional Network Types

Network Type	Full Form	Description
CAN	Campus Area Network	Connects multiple LANs within a university campus or corporate campus — larger than LAN but smaller than MAN
SAN	Storage Area Network	High-speed network dedicated to data storage devices (disk arrays, tape libraries) — used in data centers

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Networking Standards (IEEE 802)

Standard	Name	Description
IEEE 802.3	Ethernet	Wired LAN standard — defines how data is transmitted over cables
IEEE 802.4	Token Bus	LAN standard where devices share a logical token-passing bus arrangement
IEEE 802.5	Token Ring	LAN standard where a token circulates around a ring to control transmission
IEEE 802.11	WiFi	Wireless LAN standard — 802.11a/b/g/n/ac/ax (WiFi 6)
IEEE 802.15	Bluetooth / WPAN	Wireless Personal Area Network — short-range communication

IEEE = Institute of Electrical and Electronics Engineers. The 802 family covers all LAN/MAN networking standards.

Another older communication term is ISDN (Integrated Services Digital Network). ISDN was a digital telecommunication standard used to carry voice, data, and signaling over telephone networks. It is not a modern broadband technology, but it remains an important historical networking term.

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MAC Address

A MAC (Media Access Control) address is a 48-bit hardware address permanently assigned to each Network Interface Card (NIC).

• Format: AA:BB:CC:DD:EE:FF (6 pairs of hexadecimal digits)
• Unique to every network device in the world
• Works at Layer 2 (Data Link) of OSI model
• Also called physical address or hardware address
• ARP protocol maps IP addresses to MAC addresses

IP address can change (dynamic via DHCP), but MAC address is permanent (burned into hardware). However, MAC spoofing is possible via software.

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Client-Server vs Peer-to-Peer Architecture

Feature	Client-Server	Peer-to-Peer (P2P)
Structure	Central server serves client requests	All computers are equal (no central server)
Control	Centralized	Decentralized
Security	Higher (server manages security)	Lower (each peer manages own security)
Cost	Expensive (server hardware)	Cheap (no dedicated server)
Examples	Website hosting, email servers, banking systems	BitTorrent, blockchain
Scalability	Easily scalable with better servers	Difficult to manage at large scale

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Bandwidth Units

Unit	Full Form	Value
bps	Bits per second	Base unit
Kbps	Kilobits per second	1,000 bps
Mbps	Megabits per second	1,000 Kbps (home broadband)
Gbps	Gigabits per second	1,000 Mbps (fiber optic)
Tbps	Terabits per second	1,000 Gbps (internet backbone)

Note: Internet speed is measured in bits per second (Mbps), while file sizes are in bytes (MB). 1 byte = 8 bits. So 100 Mbps speed downloads at ~12.5 MB/s.

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Network Topology Comparison

Topology	Reliability	Cost	Scalability	Cable Failure Impact
Star	Good (single node failure OK)	Moderate	Easy to add nodes	Hub failure = total failure
Bus	Low	Cheap	Difficult	Main cable break = total failure
Ring	Low	Moderate	Difficult	Single break can disrupt entire ring
Mesh	Highest	Most expensive	Difficult	Multiple paths — no single point of failure
Tree	Moderate	Moderate	Good for hierarchies	Backbone failure = segment failure

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LoRaWAN & Bluetooth Versions

LoRaWAN (Long Range Wide Area Network)

• Designed for IoT (Internet of Things) devices
• Low power consumption — battery can last years
• Long range — up to 15 km in rural areas
• Low data rate (suitable for sensors, not video)
• Used in smart agriculture, smart cities, industrial monitoring

Bluetooth Versions

Version	Key Feature
Bluetooth 4.0	Introduced BLE (Bluetooth Low Energy) — used in fitness trackers, IoT
Bluetooth 5.0	2x speed, 4x range compared to 4.2 — better for smart home
Bluetooth 5.3	Latest version — improved energy efficiency, better connection quality

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Summary Points

Concept	Key Details
LAN	Local — within building, fast (Ethernet/WiFi)
WAN	Wide — country/global, Internet is biggest WAN
MAN	Metropolitan — within a city
PAN	Personal — ~10m, Bluetooth
CAN	Campus Area Network — multiple LANs within university/corporate campus
SAN	Storage Area Network — high-speed dedicated storage network (data centers)
Star Topology	All connect to central hub — most common
Bus Topology	Single backbone cable — cheap, old, single point of failure
Ring Topology	Circle — one node fails can disrupt ring
Mesh Topology	All connect to all — most reliable, most expensive
Tree Topology	Star + Bus combo — hierarchical, large organizations
Hub	Broadcasts to all (dumb) — Layer 1
Switch	Sends to specific device (smart) — Layer 2
Router	Connects different networks, uses IP — Layer 3
Bridge	Connects two LANs, filters traffic
Repeater	Amplifies weak signals to extend range
Modem	Modulator-Demodulator — analog to digital conversion
Gateway	Connects networks with different protocols
Fiber Optic	Fastest cable — uses light, up to 100 Gbps, immune to EMI
Twisted Pair (UTP)	Common LAN cable, copper, 10-1000 Mbps
Coaxial Cable	Central copper wire, shielded — Cable TV, older networks
WiFi	~100m range, home/office
Bluetooth	~10m, short-range device pairing
Satellite	Global — GPS, remote areas
IEEE 802.3	Ethernet — wired LAN standard
IEEE 802.11	WiFi — wireless LAN (a/b/g/n/ac/ax = WiFi 6)
IEEE 802.15	Bluetooth / WPAN — short-range wireless
MAC Address	48-bit hardware address — AA:BB:CC:DD:EE:FF — permanent, Layer 2
ARP	Maps IP address → MAC address
Client-Server	Centralized — server serves clients (websites, banking)
P2P (Peer-to-Peer)	Decentralized — all equal (BitTorrent, blockchain)
bps	Bits per second — base bandwidth unit
Mbps	Megabits/sec — home broadband speed
Gbps	Gigabits/sec — fiber optic speed
Tbps	Terabits/sec — internet backbone
Speed vs Size	Internet speed in bits (Mbps); files in bytes (MB); 1 byte = 8 bits
LoRaWAN	IoT — low power (years on battery), up to 15 km range, low data rate
Bluetooth 4.0	Introduced BLE (Bluetooth Low Energy) — fitness trackers, IoT
Bluetooth 5.0	2x speed, 4x range vs 4.2 — smart home
Bluetooth 5.3	Latest version — improved energy efficiency
TCP/IP	Foundation protocol of Internet
DHCP	Auto-assigns IP addresses
DNS	Domain name → IP address
ICMP	Error reporting, ping command
IPv4	32-bit, ~4.3 billion addresses (running out)
IPv6	128-bit, virtually unlimited