Computer Network

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1. Introduction to Computer Networks


A Computer Network is a collection of autonomous computing devices interconnected to exchange information using common protocols over a shared communication medium.

Applications

• Access and Process Information: Databases, online payments, e-commerce, electronic money transfers.
• Communication: Email, chat, video calls.

Advantages

• Resource Sharing: Data, programs, peripherals, computing power.
• Communication and Collaboration: Facilitates teamwork.
• Centralized Management: Easy administration of users and data.
• Data Security: Enhanced compared to other communication methods.
• Sharing Capabilities:
  • Information Sharing: Authorized users access and share data across the network.
  • Hardware Sharing: Devices like printers or scanners shared by multiple users.
  • Software Sharing: Centralized software installation on servers for network-wide access.
  • Collaboration: Enables group projects using diverse equipment.

Disadvantages

• Security Risks: Vulnerabilities to cyber threats.
• Cost: High implementation and maintenance costs.
• Complexity: Increased maintenance and management requirements.
• Downtime: Disruptions from network issues.

2. Types of Networks by Spatial Scope

Network Type	Description	Examples	Key Features
BAN (Body Area Network)	Sensors/actuators embedded in the human body for communication.	Heartbeat sensor, temperature sensor, blood pressure sensor.	Health monitoring, wireless communication.
PAN (Personal Area Network)	Devices within a person's range, wired (USB) or wireless (Bluetooth).	Computer to keyboard/mouse/printer, smartphone to computer.	Short-range, personal device connectivity.
LAN (Local Area Network)	Privately owned network in a single building or group of buildings.	Home Wi-Fi, IT faculty computer labs (Ethernet).	High data rates, low latency, homogeneous devices.
CAN (Campus Area Network)	Multiple LANs within a campus.	University LANs (IT, Civic, Admin, etc.).	Connects to public internet, campus-wide coverage.
MAN (Metropolitan Area Network)	Covers a city, often using fiber optics.	Cable TV networks, ADSL networks.	City-wide connectivity, multiple LANs.
RAN (Radio Access Network)	Connects devices via radio links, part of mobile networks.	4G, 5G networks.	Uses back-haul fiber optic connections.
WAN (Wide Area Network)	Covers large areas (country, continent).	Internet.	Lower data rates, higher latency, heterogeneous devices.

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WAN Subtypes

• MAN: City-wide network.
• Public Access Network (PAN): Publicly accessible organizational network.
• Value Added Network (VAN): Private networks for EDI with services like data validation and encryption.
• Virtual Private Network (VPN): Secure network over public infrastructure.

3. Internet and Internetworks

• Internetwork: Connects multiple networks maintained by different organizations or using different technologies.
• Internet: Global interconnected set of networks using common protocols, managed by Internet Service Providers (ISPs).
• VPN:
  • External View: Secure communication over public networks.
  • Internal View: Appears as a private network with encrypted tunnels, scalable, and cost-effective.
  • Consumer VPN: Masks IP addresses, prevents ISP tracking, circumvents geo-restrictions.

4. Specialized Networks

Storage Area Network (SAN) vs. Network Attached Storage (NAS)

Feature	SAN	NAS
Network	Dedicated high-speed network	Uses existing LAN with TCP/IP
Access Level	Block level	File level
Protocols	iSCSI, Fiber Channel	NFS, SMB
Appearance	Local drive	Network shared folder
Cost & Complexity	High	Low
Performance	High performance, scalable	Moderate performance

Controller Area Network (CAN)

• Purpose: Real-time communication for sensors, actuators, and microcontrollers.
• Applications: Automotive, railway, medical, industrial.
• Features: Peer-to-peer, priority-based broadcast, low cost, lightweight.

Intranet vs. Extranet

Feature	Intranet	Extranet
Access	Internal users only	Defined external users (e.g., partners)
Security	Firewalls, private IP addresses	Password-protected
Purpose	Internal communication	Collaboration with external stakeholders

5. Packet Switching vs. Circuit Switching

Feature	Circuit Switching	Packet Switching
Path	Dedicated path	Independent packet routing
Bandwidth	Reserved	Shared, no reservation
Latency	Low, predictable	Higher, variable
Scalability	Less scalable	Highly scalable
Example	Analog telephone networks	Internet
Efficiency	Inefficient bandwidth use	Efficient bandwidth use
Issues	None	Possible packet loss

6. Communication Media

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Guided Media

Media Type	Description	Usage	Features
Twisted Pair Cables	Two insulated wires twisted to reduce interference.	Telephone, Ethernet cables.	Inexpensive, UTP/STP variants.
Coaxial Cables	Copper core with insulation and metal shield.	TV signals, CCTV, internet.	Inexpensive, shielded.
Fiber Optic Cables	Glass fibers carrying light.	High-bandwidth networks.	High bandwidth, immune to electromagnetic noise.

Twisted Pair Cable Types

Cable Type	Shielding	Max Frequency	Max Data Rate	Speed
Cat 3	No	16 MHz	10 Mbps	10 Mbps
Cat 5	No	100 MHz	100 Mbps	100 Mbps
Cat 5e	No	100 MHz	1 Gbps	1 Gbps
Cat 6	Sometimes	250 MHz	1 Gbps	1 Gbps
Cat 6a	Sometimes	500 MHz	10 Gbps	10 Gbps
Cat 7		600 MHz	40 Gbps	10 Gbps
Cat 8		2 GHz	25/40 Gbps	40 Gbps

Fiber Optic Variants

• Single-Mode: Narrow core, LASER source, high bandwidth, costly.
• Multi-Mode: Larger core, LED source, lower bandwidth, cheaper.

Unguided Media

Media Type	Description	Usage
Microwave Signal	High-frequency radio signals, line-of-sight.	Satellite, telecom backhaul.
Satellite System	Relays data via satellites.	Global communication.
Cellular Technology	Radio communication via ground towers.	Mobile networks.
Infrared Technology	Infrared light for line-of-sight.	Short-range communication.

7. Networking Hardware

Basic Hardware

• Network Interface Card (NIC): Connects computers to networks, varies by medium and bandwidth.
• Cables & Connectors: ST, MT-RJ, SC, RJ45, LC, SFP/SFP+/XFP transceivers.
• Servers: Deliver data/services to clients.
• Workstations: High-performance client computers.

Inter-Networking Hardware

Device	Function	OSI Layer	Features	Comparison
Repeater	Amplifies signals for longer distances.	Physical	Simple, low cost.	N/A
Hub	Connects multiple devices, broadcasts data.	Physical	Half-duplex, limited bandwidth.	Hub vs. Switch: Hub broadcasts, Switch forwards selectively.
Switch	Connects devices, forwards data to specific ports.	Data Link	Full-duplex, high bandwidth.	Switch vs. Bridge: More ports, hardware forwarding.
Bridge	Connects two LANs.	Data Link	Software forwarding, fewer ports.	Bridge vs. Switch: Fewer ports, slower.
Router	Connects networks, forwards packets using IP.	Network	Firewall features, complex configuration.	Router vs. Switch/Bridge: Uses IP, manipulates frames.
Gateway	Converts protocols between networks.	Application	Links dissimilar networks.	N/A
Modem	Converts analog to digital signals.	Physical	Internet access via phone lines.	N/A
Access Point	Provides wireless access to wired networks.	Data Link	Wireless connectivity.	N/A

8. MAC Address and Ethernet

• MAC Address: 48-bit unique identifier for NICs, used in Data Link layer (e.g., 00:00:00:56:BD:47).
• Ethernet:
  • Standardized by IEEE 802.3 (1985).
  • Uses bus/star topology, CSMA/CD for collision detection.
  • Classic Ethernet: 10 Mbps, shared medium, collisions.
  • Switched Ethernet: No collisions, full-duplex, higher bandwidth.

Ethernet Frame

• Preamble: 8 bytes for synchronization.
• Destination/Source Address: MAC addresses.
• Type: Specifies higher-level protocol.
• Body: 46–1500 bytes.
• CRC: Error detection.

9. Network Topologies

Topology	Description	Advantages	Disadvantages
Point-to-Point	Direct node connection.	Full bandwidth.	Limited to two nodes.
Star	Nodes connect to a central hub/switch.	Easy to add nodes, fault isolation.	Central device failure.
Ring	Closed loop, token-based.	Low collisions, easy expansion.	Node failure affects network, latency.
Bus	Nodes share a single medium.	Low cost, simple.	High collisions, single point of failure.
Hybrid	Combines multiple topologies.	Flexible, scalable.	Complex management.

10. Network Architectures

Peer-to-Peer

• Features: No central infrastructure, equal nodes.
• Advantages: Easy setup, reliable, low cost.
• Disadvantages: Security and backup challenges, illegal content distribution.

Client-Server

• Features: Centralized server manages resources.
• Advantages: Centralized control, secure, easy backups.
• Disadvantages: High cost, single point of failure, traffic congestion.

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