1.2 Network Edge

Access Networks

  • Connect edge devices to first hop router and larger Internet.

  • Types of access networks:

    • Residential

    • Institutional (e.g., companies, municipalities)

    • Mobile (e.g., cellular, Wi-Fi)

  • Key considerations:

    • Transmission rate

    • User bandwidth sharing

Cable Access Networks

  • Connect multiple homes using a single cable via frequency division multiplexing (FDM).

  • Asymmetric transmission rates:

    • Downstream: 40 Mbps to 1.2 Gbps

    • Upstream: 30 to 100 Mbps

  • Shared network; usage by neighbors can affect performance.

Digital Subscriber Line (DSL)

  • Utilizes existing phone lines; reduces bandwidth sharing.

  • Asymmetric transmission rates:

    • Downstream: 24 to 52 Mbps

    • Upstream: 3.5 to 16 Mbps

  • Performance decrease over distance; effective within 3 miles from central office.

Home Networking

  • Typical setup involves a DSL/cable modem connected to various device links:

    • Wired Ethernet: 100 Mbps or Gbps

    • Wi-Fi: Tens to hundreds of Mbps

Wireless Networks

  • Types:

    • Local (Wi-Fi): 10 to 100 meters, speeds from 11 to 450 Mbps.

    • Wide Area (Cellular 3G/4G/5G): Tens of km, speeds vary from 1 to 100 Mbps.

Enterprise Networks

  • Larger scale than home networks; multiple switches/routers for numerous devices.

  • Data center networks connect numerous servers at hundreds of Gbps.

Packet Transmission

  • Data broken into smaller packets for transmission.

  • Packet includes data plus header information.

    • Packet length: l bits, typical value: 1,500 bytes.

    • Transmission rate: r bits per second.

    • Transmission time = lr\frac{l}{r}.

Physical Media Characteristics

  • Types:

    • Guided (copper, fiber optic) and unguided (radio).

  • Cable types:

    • Twisted Pair: Hundreds of Mbps, susceptible to noise.

    • Coaxial: Hundreds of Mbps for cable networks.

    • Fiber Optics: Hundreds of Gbps, low error rates, high cost.

Wireless Transmission

  • Wireless links transmit signals via electromagnetic spectrum without physical wires.

  • Challenges: interference, fading, noise.

  • Types of Wireless Networks:

    • Wi-Fi: up to hundreds of Mbps; range ≈ 100m.

    • 4G: tens of Mbps; range ≈ 10 miles.

    • Bluetooth: 1-2 Mbps; range ≈ 5-10m.