Wi-Fi

Otherwise known as 802.11, which is a standard defining the MAC and PHY layers for wireless LAN.

The technical specifications aside, which one may helpfully consult the Wikipedia page, this page is more of a quick guide to what the technical meanings of certain nomenclature are.

• 802.11 is the mother-document, that also defines the weak WEP (uses RC4, weakened from high IV reuse due to low 24-bit width).
• 802.11i defines the interim WPA and updated WPA2 (uses AES-CCMP with PSK). WPA2 involves a 4-way handshake:
  1. Derive the symmetric pre-shared key (PSK), typically from SHA-1 hash of Wi-Fi password.
  2. Derive a symmetric ephemeral session key (Pairwise Transient Key; PTK) using client and AP nonces. Client appends MAC together with message containing the nonce.
  3. AP sends symmetric key (Group Temporal Key; GTK) for decrypting multicast messages, using PTK.
• 802.1X defines the use of Extensible Authentication Protocol (EAP) framework over specific MAC layers (including 802.11 networks). PEAP (Protected EAP) itself uses EAP over TLS tunnel. Involves an authentication server, e.g. RADIUS.

A Service Set is a logical grouping of network devices sharing the same Service Set Identifier (SSID). A Basic Service Set (BSS) additionally defines the physical-layer characteristics, formed from a single access point.

Moving between BSS is typically termed roaming. Client typically disconnects first before performing roaming, which results in connection interrupts. An Extended Service Set (ESS) can be defined by grouping BSS on the same logical link control layer, with optionally centralized authentication using 802.1X.

"Seamless Roaming" (between BSS) is defined by the 802.11k/v/r protocols. This TP-Link page summarizes it nicely and Apple's page goes a bit more technical, with Wikipedia providing more context. Summarizing here:

• 802.11k: AP responds to client request for site report (i.e. list of nearby APs that may provide better signal/throughput). Reduces client roaming time.
• 802.11v: AP pushes network load information of nearby APs to client, upon detection of imminent disconnection. Makes client network-aware for load balancing.
  • Also defines power saving methods, e.g. how long to stay associated with AP with no ongoing traffic.
• 802.11r: Specifies fast BSS transitions (FT). Caches part of PMK/PSK in all APs of the BSS to perform PTK derivation + QoS, while simultaneously performing authentication and reassociation.
  • Non-802.11r BSS transitions require separate (1) authentication + reassociation with AP, (2) 802.1X negotiation for PMK derivation, (3) PTK derivation, (4) QoS admission control for QoS streams.
  • 802.11e (HCF/EDCA): Provides QoS mechanisms to prioritize different traffic classes. Modifies the MAC layer.