Local Area Network (LAN) – Detailed Explanation
Definition of LAN:
A Local Area Network (LAN) is a network that connects computers and other devices within a limited geographical area, such as a home, office, school, or building. LANs enable resource sharing (e.g., files, printers, internet) and seamless communication among connected devices.
Characteristics and Scope
- Geographic Coverage: Typically within a single building or campus (usually up to a few hundred meters).
- Ownership: Owned, managed, and maintained by a single organization or individual.
- High Data Transfer Speeds: Commonly operates at 100 Mbps, 1 Gbps, or even 10 Gbps.
- Low Latency: Fast and efficient communication due to proximity of devices.
Example: In a corporate office, all employee computers, printers, and servers are connected to form a LAN. Employees can access shared documents and print from any workstation.
Components of a LAN
| Component | Role / Description | Example |
|---|---|---|
| Switch | Central device interconnecting computers and other networked devices within the LAN | 24-port Cisco switch in an office |
| Router | Connects the LAN to external networks (e.g., the Internet) | ISP-provided router at home |
| Access Point (AP) | Provides wireless connectivity within the LAN | Wi-Fi AP for smartphones and laptops |
| End Devices | User devices such as computers, laptops, IP phones, printers, servers | PCs, network printers, file servers |
Example: John’s office LAN includes 1 switch, 2 access points, 10 desktop PCs, a printer, and a file server.
LAN Technologies
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Ethernet (IEEE 802.3): Most common wired LAN technology.
- Speeds: 10 Mbps (Ethernet), 100 Mbps (Fast Ethernet), 1 Gbps (Gigabit Ethernet), 10 Gbps (10 Gigabit Ethernet)
- Wi-Fi (IEEE 802.11): For wireless LANs. Standards include 802.11n, 802.11ac, 802.11ax (Wi-Fi 6).
LAN Topologies
- Star Topology: All devices connect to a central switch/hub (most common today).
- Bus Topology: Single cable backbone; rare today.
- Ring Topology: Devices connected in a closed loop.
- Mesh Topology: Devices interconnected for redundancy.
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Physical vs. Logical Topology:
- Physical: Actual cable/device layout.
- Logical: How data flows (e.g., Ethernet = logical bus, physical star).
LAN Protocols
- Ethernet (IEEE 802.3): Frame-based protocol for LAN traffic.
- ARP (Address Resolution Protocol): Resolves IP addresses to MAC addresses.
- STP (Spanning Tree Protocol): Prevents loops in networks with redundant links.
Example: When John’s PC sends data to a printer, Ethernet and ARP ensure data reaches the correct device without loops (STP prevents broadcast storms).
Media Types in LAN
- Twisted Pair Cables: Cat5e, Cat6, Cat6a, Cat7 for Ethernet connections.
- Fiber Optics: High-speed, long-distance LAN segments (e.g., between buildings).
- Wireless Media: Radio waves used in Wi-Fi networks.
LAN Design and Architecture
- Network Segmentation & VLANs: LANs can be divided into Virtual LANs (VLANs) to separate traffic for security/performance.
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Hierarchical Design Model:
- Core Layer: High-speed backbone.
- Distribution Layer: Policy-based connectivity (routing, access control).
- Access Layer: Connection point for end devices.
Example: A three-tier campus LAN: core connects distribution switches, which connect access switches; access switches connect end devices.
LAN Performance Factors
- Bandwidth: Maximum network link capacity.
- Throughput: Actual data transfer rate experienced by users.
- Latency: Delay in data transmission.
- Jitter: Variability in latency.
Security in LANs
- Access Control: Authenticate users/devices before granting network access.
- VLAN Security: Isolate sensitive data on separate VLANs.
- Port Security: Limit devices connecting to a switch port (MAC-based filtering).
Common LAN Issues and Troubleshooting
- Collisions: Two devices transmit simultaneously (rare with switches).
- Congestion: Excessive data slows network performance.
- Broadcast Storms: Excessive broadcast traffic overwhelms the network.
- Loops: Multiple switch paths causing frame duplication (STP prevents this).
LAN Management Tools
- Network Monitoring Software: e.g., SolarWinds, PRTG, Cisco Prime.
- SNMP (Simple Network Management Protocol): Monitors device status and health.
- Syslog: Collects and analyzes device log messages for troubleshooting.
Emerging Trends in LANs
- Software-Defined Networking (SDN): Centralized, programmable control over LAN traffic.
- Power over Ethernet (PoE): Provides power and data to devices (e.g., APs, IP cameras) via Ethernet cable.
When and Where to Use a LAN?
LANs are ideal for environments where multiple devices need to communicate or share resources within close proximity—offices, homes, schools, and hospitals.
Use Case: A school sets up a LAN so students in computer labs can access educational resources, print assignments, and use the internet securely.
Key Points & Tips for the Exam
- Know the definition and key features of a LAN.
- Identify main components (switch, router, end devices).
- Understand common technologies (Ethernet, Wi-Fi) and media types.
- Distinguish between topologies and explain their pros/cons.
- Explain how VLANs and port security improve LAN performance and security.
- Recognize common troubleshooting scenarios and management tools.
- Be aware of emerging technologies (SDN, PoE).