Network Fundamentals - LAN (Local Area Network)
Designing a network is like planning a transportation system: you must decide how “roads” connect cities (topology) and which “traffic controllers” (devices) will manage the flow of data. Understanding star, bus, and ring topologies — as well as switches and routers — is fundamental to networking.
LAN Topologies
Star Topology – The Modern Standard
How It Works
In a star topology, every device (computer, printer, IoT device) connects to a central point — typically a switch or hub.
When one computer sends data, it first goes to the central device, which then forwards it to the intended recipient.
Technical Details
- Physical Layer: Uses twisted-pair Ethernet cables or wireless connections.
- Logical Topology: Can be Ethernet, Fast Ethernet, or Gigabit Ethernet.
- Central Device: Usually a switch (smarter) rather than a hub (broadcasts to all).
Advantages
Fault Isolation: If one cable fails, only that device is affected.
Scalability: Easy to add or remove devices without disturbing the network.
Performance: Dedicated links reduce collisions (especially with switches).
Troubleshooting: Easy to spot which connection has failed.
Disadvantages
Single Point of Failure: If the switch goes down, the entire network stops.
More Cabling: Requires more cable than bus topology (one cable per device).
Where You See It
Homes & Offices: Your Wi-Fi router is the center, forming a star topology.
Data Centers: Switches connect servers in a star pattern.
Bus Topology – The Classic Approach
How It Works
A bus topology uses one central cable — called a backbone — that runs through the network.
Each device connects to this backbone, and data travels along it until it reaches its destination.
Technical Details
Media: Coaxial cable was commonly used in early Ethernet (10Base2, 10Base5).
Access Method: CSMA/CD (Carrier Sense Multiple Access / Collision Detection) — devices listen before transmitting, but collisions still happen.
Advantages
Low Cost: Requires less cable than star topology.
Simple Layout: Easy to set up in small environments.
Disadvantages
Difficult Troubleshooting: A single cable fault can bring down the entire network.
Performance Drops: Collisions increase as more devices join.
Obsolete: Rarely used today — replaced by star topology with switches.
Where You See It
Legacy Networks: Small offices in the 1980s/90s.
Temporary Labs: Simple setups where cost is a major concern.
Ring Topology – The Data Highway
How It Works
Devices in a ring topology are connected in a closed loop.
Each device has two neighbors, and data travels in one direction (unidirectional) or two (bidirectional in dual-ring).
Each device acts as a repeater, boosting the signal before passing it along — preventing data loss over distance.
Technical Details
Protocols: Token Ring (developed by IBM), FDDI (Fiber Distributed Data Interface).
Access Control: Token-passing — only the device holding the token can transmit, avoiding collisions.
Advantages
Predictable Traffic: Each device gets equal access, making performance consistent.
Reduced Collisions: Token passing eliminates data collisions.
Good for Large Distances: Signal regeneration at each node.
Disadvantages
Sensitive to Failure: If one node fails, the whole ring may break (unless using a dual-ring or bypass mechanism).
Complex Maintenance: Adding/removing devices is harder than in a star network.
Where You See It
Industrial & Metro Networks: FDDI rings in MANs (Metropolitan Area Networks).
Specialized Environments: Factory floors where predictable latency is important.
Switch – The Brain of the LAN
A switch is an intelligent device that connects multiple devices within a local area network (LAN) and directs traffic efficiently.
How It Works
MAC Address Table: The switch learns which device (MAC address) is connected to which port.
When a frame arrives, the switch checks its table and forwards the data only to the correct port.
Benefits
Reduces Network Congestion: No unnecessary broadcasting.
Improves Security: Data goes only where it’s supposed to.
Supports VLANs: Logical segmentation of networks for better security & management.
Types of Switches
Unmanaged: Plug-and-play, no configuration.
Managed: Allows configuration, monitoring, VLAN setup, QoS, etc.
Router – The Traffic Controller
A router connects different networks together — usually your internal LAN to the internet (WAN).
How It Works
Uses IP addresses (Layer 3) to decide where to send data.
Maintains a routing table with the best paths to different networks.
Capabilities
NAT (Network Address Translation): Lets multiple devices share one public IP.
Firewall Functions: Can block or allow traffic based on rules.
Dynamic Routing Protocols: OSPF, BGP, RIP for larger networks.
Further Learning
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