Local Area Networks (LAN)

Local Area Network (LAN)

  • Definition: A network that connects multiple devices within a short physical distance to share data. It can range from 2 devices to thousands. For example, a home network connecting computers, printers, and smart TVs is a LAN.

  • LANs enable fast data transfer within the network. Speeds can range from 10 Mbps to 1000 Mbps (1 Gbps) or even faster.

LAN Intro, Topologies, and Outline

  • Topics covered:-

    • LAN Introduction

    • Example: Satellite broadcasting

    • Channel allocations

LAN Components and Applications

  • Components:-

    • Shared transmission medium (though not always required in modern LANs) such as cables or wireless signals.

    • Stations (computers, printers, servers, etc.). Each station has a network interface card (NIC) to connect to the network.

  • Modern LANs may not always use a shared transmission medium to enhance performance. Switches, for example, allow multiple devices to communicate simultaneously without collisions.

  • Applications:-

    • Personal Computer LANs:-

      • Resource sharing (e.g., printers, scanners). Allows multiple users to access the same resources.

      • Information sharing (e.g., files, documents). Facilitates collaboration and data exchange.

      • \"Limited\" data rate (10Mbps – 1000Mbps). Though speeds can be significantly higher in modern LANs.

    • Backend Networks:-

      • Interconnecting large systems (mainframes and large storage devices). Supports high-speed data transfer between critical systems.

      • High data rate. Essential for data-intensive applications.

    • Storage Area Networks (SAN):-

      • Separate network for storage needs (hard disks, tape libraries, CD arrays). Optimizes storage management and performance.

      • Detaches storage tasks from specific servers. Allows for centralized storage and improved scalability.

Satellite Broadcasting

  • Simplified look at satellite broadcasting as an introduction to Local Area Networking and multi-access communication:

  • Many users share a single channel. This is similar to how devices share a LAN channel.

  • Propagation at the speed of light (300,000 km/sec300,000 \, \text{km/sec})

    • Distance travelled is large (35,880km for conventional TV satellites), resulting in round trip times of ~270msec. The significant delay affects communication protocols .

    • Bandwidth, typically 3.5Gbps-22Gbps, is currently 100x higher than typical LAN-based networks because it is less limited by the speed of local infrastructure. Satellites can support higher data rates due to fewer physical constraints.

Satellite Broadcasting - Shared Channel

  • Many users share a single channel.-

    • Cost is the same regardless of the distance between sender and receiver. Satellite costs have dropped dramatically. Makes it economical for broadcasting over large areas.

    • Satellite acts as a repeater, amplifying and re-broadcasting signals. This ensures that the signal reaches all users within the coverage area.

    • Collisions occur when two stations broadcast simultaneously, resulting in garbage. A sender can listen to the re-broadcast of their own packets to detect collisions. Similar to collision detection in Ethernet.

    • No acknowledgements are used. Simplifies the protocol but makes reliable delivery difficult. Error detection is essential.

    • Users are uncoordinated and communicate only via the channel. This is typical in broadcast scenarios.

Advantages of Satellite Channel Allocation

  • The satellite channel must control its own allocation. This ensures efficient use of bandwidth.

  • Advantages of this approach:

    • Global coverage: Satellites can cover large geographical areas.

    • Cost-effective for broadcasting: Distributing content to many users simultaneously is economical.

    • High bandwidth: Supports high data rates for multimedia applications.

Channel Allocation Strategies

  • Fixed Assignment: Each user is assigned a fixed portion of the channel. Simple but inefficient if some users are idle.

  • Demand Assignment: Channel is allocated dynamically based on user demand. More complex but more efficient.

  • Random Access: Users transmit randomly and deal with collisions. Simple but can lead to congestion.

Ethernet

  • Dominant LAN technology. Widely used in homes, offices, and data centers.

  • Specifies the physical and data link layers.

  • Originally developed by Xerox PARC in the 1970s.

Ethernet Frame Format

  • Preamble: 7 bytes of alternating 1s and 0s for synchronization.

  • Start Frame Delimiter (SFD): 1 byte indicating the start of the frame.

  • Destination MAC Address: 6 bytes specifying the recipient's hardware address.

  • Source MAC Address: 6 bytes specifying the sender's hardware address.

  • Length/Type: 2 bytes indicating either the frame length or the protocol type.

  • Data: 46-1500 bytes of payload.

  • Frame Check Sequence (FCS): 4 bytes for error detection.

Ethernet Evolution

  • Original Ethernet (10Base5): 10 Mbps, baseband signaling, coaxial cable.

  • Fast Ethernet (100BaseT): 100 Mbps, twisted pair or fiber optic cable.

  • Gigabit Ethernet (1000BaseT): 1 Gbps, twisted pair or fiber optic cable.

  • 10 Gigabit Ethernet (10GBaseT): 10 Gbps, twisted pair or fiber optic cable.

  • 40 Gigabit Ethernet (40GBaseT) and 100 Gigabit Ethernet (100GBaseT) Even faster speeds for high-bandwidth applications.

CSMA/CD (Carrier Sense Multiple Access with Collision Detection)

  • Used in early Ethernet versions.

  • Stations listen to the channel before transmitting (Carrier Sense).

  • Multiple stations can access the channel (Multiple Access).

  • If a collision is detected during transmission, stations stop transmitting and send a jam signal (Collision Detection).

  • After a random backoff time, stations retransmit.

Ethernet Standards

  • IEEE 802.3: Defines the Ethernet standard.

  • IEEE 802.3u: Fast Ethernet.

  • IEEE 802.3z: Gigabit Ethernet over fiber.

  • IEEE 802.3ab: Gigabit Ethernet over twisted pair.

  • IEEE 802.3ae: 10 Gigabit Ethernet.

Full-Duplex Ethernet

  • Allows simultaneous transmission and reception.

  • Requires switches instead of hubs.

  • Eliminates collisions, improving performance.

Virtual LANs (VLANs)

  • Logically separate networks within a physical LAN.

  • Improve security and network management.

  • Can be based on port, MAC address, or protocol.

Advantages of VLANs

  • Security: Isolate sensitive traffic.

  • Performance: Reduce broadcast traffic.

  • Flexibility: Easily reconfigure network without physical changes.

  • Management: Simplify network administration.

Example Scenario to VLANs

  • A company has different departments (e.g., Marketing, Engineering, Sales).

  • Each department can be assigned to a separate VLAN.

  • Traffic between VLANs can be