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Wireless & Mobile

What changes when the link is the air. This module starts with why radio is a harder medium than a wire: shared spectrum, multipath, and the hidden terminal. It then builds Wi-Fi from the 802.11 architecture through CSMA/CA to security and roaming, and moves on to cellular networks: cells, the 4G and 5G cores, and how a phone keeps its connections alive as it moves.

What you will be able to answer​

  • Why is wireless harder than wired, and what do path loss, multipath and interference do to a signal?
  • What is the hidden terminal problem, and why can a radio not detect collisions the way Ethernet does?
  • How do BSS, ESS, SSID and BSSID differ, and what happens between scanning and association?
  • Why does 802.11 use backoff, IFS timing, NAV and RTS/CTS instead of collision detection?
  • How did Wi-Fi security move from WEP to WPA3, and what do the 4-way handshake and 802.1X add?
  • What do 802.11r, k and v change when a client roams between access points?
  • How do cells, the RAN and the core fit together, and how does the 5G core differ from the 4G EPC?
  • What happens when a phone attaches, and what do bearers and SIM authentication do?
  • How does handover work, and why does hysteresis prevent ping-pong between cells?
  • How do Mobile IP, GTP anchoring and QUIC connection migration keep a session alive when the address changes?
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