Networking Fundamentals

1. Introduction to Computer Networks

1.1 Definition of a Computer Network

• A computer network is a collection of two or more interconnected autonomous computing devices that exchange information using protocols over a shared communication medium.
• Key Terms:
  • Node: Any device on a network (e.g., computers, routers).
  • Host: Typically refers to a computer on the network.
  • Data Transfer Rate: Speed at which data moves across the network; critical for network performance.
• Note: A single computer with peripherals (e.g., printers) is not a network.

1.2 Importance of Computer Networks

• Facilitates communication and resource sharing, shrinking geographical barriers.
• Enables online activities: email, e-commerce, bill payments, data downloads.
• Transforms communication: supports email, voicemail, video conferencing.

2. Benefits and Risks of Networking

2.1 Benefits of Computer Networks

• Information Sharing: Authorized users access and share data across networked computers.
• Hardware Sharing: Devices like printers or scanners are shared, reducing costs.
• Software Sharing: Centralized software installation on servers allows access by multiple users.
• Collaborative Environment: Supports group projects by combining diverse equipment capabilities.
• Additional Advantages:
  • Online data processing, retrieval, and transactions (e.g., credit card checks, EFT).
  • Easy user management (adding/removing users).
  • Distributed task processing via data exchange.
  • Enhanced data security compared to other communication methods.

2.2 Risks of Computer Networks

• Security Threats:
  • Hackers and malicious software (e.g., viruses, worms, Trojan horses).
• Cost and Complexity:
  • High setup and maintenance costs.
  • More complex than standalone systems.
• Reliability Issues:
  • Equipment malfunctions and system failures.

Aspect	Benefits	Risks
Sharing	Info, hardware, software sharing	Security breaches (hackers, malware)
Cost	Cost-efficient resource use	High setup/maintenance costs
Management	Easy user/task management	Complex maintenance
Reliability	Distributed processing, secure data	Equipment/system failures

3. Data Transmission Methods

3.1 Circuit Switching

• Definition: Establishes a dedicated connection (circuit) between source and destination before data transfer.
• Process:
  • Connection setup: Routers/switches reserve bandwidth.
  • Data transfer: Sent over the circuit without destination address (path is pre-known).
  • Connection closure: Circuit is closed post-transmission.
• Example: Analog telephone networks.
• Characteristics:
  • Guaranteed bandwidth, no packet loss.
  • Inefficient for bursty data (e.g., internet traffic).

3.2 Packet Switching

• Definition: Data is divided into self-contained packets with destination addresses, sent independently.
• Process:
  • Source breaks messages into packets.
  • Packets travel independently via routers/switches, which use addresses to forward them.
  • Destination reassembles packets.
• Example: Internet, postal mail analogy (letter in an envelope).
• Characteristics:
  • Efficient for variable traffic.
  • Possible delays or packet loss due to independent routing.

Feature	Circuit Switching	Packet Switching
Connection	Dedicated circuit before transfer	No dedicated circuit; independent packets
Data Flow	Continuous, no addressing needed	Packets with addresses, reassembled
Efficiency	Inefficient for bursty data	Efficient for variable traffic
Example	Telephone network	Internet

4. Categorizing Networks

4.1 Network Types by Spatial Scope

• Local Area Network (LAN): Confined to a small area (e.g., building).
• Wide Area Network (WAN): Covers large geographical areas (e.g., country, continent).
• Key Difference: LANs are localized; WANs connect multiple LANs over long distances.

4.2 Types of Networks

4.2.1 Local Area Networks (LANs)

• Definition: Networks spanning a small area, typically within a building or group of buildings.
• Characteristics:
  • Privately owned, locally administered.
  • High data rates, low latency due to short distances.
  • Cost-effective, less focus on efficiency.
  • Homogeneous environment (similar devices/protocols).
• Examples: Ethernet, Token Ring, FDDI, 802.11 wireless.
• Design Goals:
  • Operate in limited geographic areas.
  • Provide high-bandwidth multi-access.
  • Ensure full-time local service connectivity.
  • Connect adjacent devices.
• Components: Router, bridge, hub, Ethernet switch, repeater.

4.2.2 Wide Area Networks (WANs)

• Definition: Networks covering large geographical areas (e.g., countries, continents).
• Characteristics:
  • Lower speeds compared to LANs.
  • Higher delays and costs due to distance.
  • Requires scalability and efficiency.
  • Heterogeneous (diverse traffic, hosts, administration).
• Design Goals:
  • Long-distance communication.
  • Access via serial interfaces at lower speeds.
  • Full/part-time connectivity for distant devices.
• Components: Router, communication server, modem, CSU/DSU, TA/NT1.
• Example: The Internet (network of networks).

4.2.3 Other WAN Types

• Metropolitan Area Network (MAN):
  • Covers a city/town.
  • Historically used DSL/ADSL, now uses fiber optic/twisted pair cables.
  • Provides high-speed Internet, cable TV services.
• Virtual Private Network (VPN):
  • Uses public infrastructure (e.g., Internet) for secure private access.
  • Employs encryption/security mechanisms for authorized access.
  • Cost-effective, scalable, supports remote work.
• Other Types (less focus for exams):
  • Public Access Network (PAN), Value Added Network (VAN).

Network Type	Scope	Speed	Ownership	Example
LAN	Small (building)	High	Private	Ethernet
WAN	Large (country+)	Low	Mixed	Internet
MAN	Medium (city)	High	Mixed	City fiber network
VPN	Variable (Internet)	Variable	Private	Corporate VPN

4.3 The Internet

• Definition: A global internetwork (network of networks) connecting tens of thousands of networks via routers.
• Characteristics:
  • Uses common protocols for interoperability.
  • Managed by Internet Service Providers (ISPs).
  • Requires boundary devices for security/accounting.
• Structure: Hierarchical communication via interconnected networks.

5. Internetwork

• Definition: A network formed by connecting two or more heterogeneous networks.
• Example: The Internet is the largest internetwork.

---

Rationale for Content Selection

• Key Concepts Prioritized: Definitions (e.g., computer network, LAN, WAN), data transmission methods (circuit vs. packet switching), and network types are foundational and likely to be tested in exams due to their centrality to networking.
• High-Yield Details: Benefits/risks, LAN/WAN characteristics, and the Internet’s structure are emphasized for their practical and theoretical importance.
• Tables for Clarity: Used to compare circuit vs. packet switching, benefits vs. risks, and network types, as these are ideal for quick memorization and exam recall.
• Exclusions: Instructor details, recommended readings, and incomplete sections (e.g., VPN connection diagram) were omitted as they are not exam-relevant or lack sufficient detail.
• Clarifications: Minor additions (e.g., circuit switching inefficiency for bursty data) were included based on general networking knowledge to enhance understanding without relying on external sources.