Notes on Local Area Networks (LANs)

Local Area Network (LAN) Overview

  • Definition: A Local Area Network (LAN) is a network that connects computers and devices in a limited geographical area, such as a building or campus.
  • Key Components:
  • Devices: Computers, printers, servers
  • Networking Equipment: Switches, routers, hubs

LAN Applications

  • Shared Transmission Medium:
  • Traditionally LANs utilized a shared transmission medium, but modern LANs often do not.
  • Types of LANs:
  • Personal Computer LANs:
    • Share resources (printers, files)
    • Limited data rates (10Mbps – 1000Mbps)
  • Backend Networks:
    • Interconnect large systems (e.g., mainframes, storage) with high data rates
  • Storage Area Networks (SANs):
    • Dedicated networks for storage needs, separating storage from servers

LAN Topologies

  • Common Topologies:
  • Bus: All devices share a single communication line.
    • Data flows in both directions and terminates at both ends.
  • Ring: Devices are connected in a closed loop.
    • Frames circulate around until they reach their destination.
  • Star: Each device connects to a central node (hub or switch).
    • Central node manages data traffic and can operate as a broadcast or intelligent device.
  • Tree: Hybrid structure combining star and bus topologies.

Frame Transmission Mechanisms

  • Bus Transmission:
  • A device transmits while others receive; non-target devices ignore the frame.
  • Ring Transmission:
  • A frame circulates around until it reaches its designated address.
  • Destination device copies the frame and reabsorbs it.

Central Nodes in LANs

  • Hubs:
  • Connect devices in star topology, repeating incoming signals to all outputs.
  • Simple, but can cause collisions; lacks the intelligence of a switch.
  • Switches:
  • More complex than hubs; facilitate point-to-point connections, reducing collisions.
  • Manage multiple transmissions effectively.

Ethernet Overview

  • Ethernet Standards:
  • Part of the IEEE 802.3 family.
  • Supports different speeds and types (e.g. 10Base5, 100Base-T).
  • Collision Detection:
  • Uses CSMA/CD (Carrier Sense Multiple Access with Collision Detection) to manage transmissions and reduce collisions.
  • Implement binary exponential back-off on collisions.

Channel Allocations

  • Traditional Schemes:
  • Polling: A method where a central entity grants access to transmission.
  • Multiplexing: Includes frequency division (FDMA) and time division (TDMA).
  • Contention-based:
  • Allow stations to transmit whenever the channel is free (e.g., ALOHA protocol).

Bridging and Interconnecting LANs

  • Bridges:
  • Operate at Data Link Layer (OSI Layer 2).
  • Connect differing LAN types and protocols.
  • Multiple LANs:
  • Organizations may utilize multiple LANs for isolation, performance, and security.

Advantages & Challenges of LANs

  • Advantages:
  • Improved performance by limiting traffic to smaller groups.
  • Enhanced security by isolating sensitive data.
  • Challenges:
  • Managing network resources and ensuring seamless communication between different LANs with various technologies.