Notes on Networking at the Edge

Introduction to Access Networks

• Definition: Connects edge devices (hosts) to the first hop router/internet.
• Types of access networks:
  • Residential access networks (e.g., home networks)
  • Institutional access networks (e.g., companies, educational institutions)
  • Mobile access networks (e.g., cellular and Wi-Fi networks)

Access Networks Overview

• Focus: How devices connect to the larger global internet.
• Important considerations:
  • Bit transmission rate (speed of the network)
  • Degree of user sharing of the network.

Cable Access Networks

• Example: Comcast cable access.
• Uses frequency division multiplexing (FDM) allowing multiple homes to connect through a single cable.
• Asymmetrical design: Faster downstream (to home) than upstream (from home).
  • Typical downstream rates: 40 Mbps to 1.2 Gbps.
  • Typical upstream rates: 30 to 100 Mbps.
• Shared network: Neighbor's usage can affect your bandwidth.

Digital Subscriber Line (DSL)

• Utilizes existing phone lines (twisted pair).
• Central office: Direct connection without sharing bandwidth with neighbors.
• Asymmetrical transmission rates:
  • Downstream: 24 to 52 Mbps.
  • Upstream: 3.5 to 16 Mbps, depending on distance from the central office (≤3 miles).

Home Networking

• Typical home setup:
  • DSL/cable link connects to a modem.
  • Modem connects to a router (wired and wireless links) for internal devices.
  • Wired Ethernet: 100 Mbps or Gbps.
  • Wi-Fi: Tens/hundreds of Mbps.

Wireless Networks

• Two classes of wireless networks:
  1. Local Wireless Networks (Wi-Fi): Operate 10-100 meters, speeds from 11 to 450 Mbps.
  2. Wide Area Networks (3G, 4G, 5G): Operated by cellular networks, transmission rates from 1 Mbps to tens of Mbps over kilometers.

Enterprise Networks

• More complex than home networks:
  • Mix of Ethernet and Wi-Fi links.
  • Multiple switches and routers to handle many connected devices.
  • Includes data center networks with high-speed connections (hundreds of Gbps).

Transmission of Data Packets

• Data is sent in packets:
  • Packet = Data + Header.
  • Typical packet size: 1500 bytes.
  • Transmission rate (r): Varies by network type (e.g., gigabits per second for Ethernet, megabits for 3G).
  • Transmission time = Packet size (l) / Transmission rate (r).

Physical Media Overview

• Types of physical media:
  1. Guided Media: Physical wires/cables (copper, fiber).
  2. Unguided Media: Wireless signals (radio waves).
• Twisted Pair: Handles phone and Ethernet signals; susceptible to noise.
• Coaxial Cable: Used for cable networks; operates at hundreds of Mbps.
• Fiber Optics: Carries light pulses; operates at hundreds of Gbps with low error rates.

Wireless Communication Challenges

• Wireless signals:
  • Subject to interference and fading.
  • Propagation delays and eavesdropping risks.
• Popular wireless technologies include:
  • Wi-Fi: Up to hundreds of Mbps, tens of meters.
  • 4G Cellular: Tens of Mbps, up to 10 miles.
  • Bluetooth: 1-2 Mbps over short distances (5-10 meters).
  • Terrestrial Microwave and Satellite Links: Operate at tens of Mbps with noticeable delays for satellites.

Conclusion

• Summary of access networks and physical media setup.
• Next discussion: Moving into the network core.