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WiFi6E-TheStack.md

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Below is a simplified view of the Wi-Fi 6E (IEEE 802.11ax in the 6 GHz band) protocol stack, along with brief layer responsibilities. Although Wi-Fi 6E specifically targets the 6 GHz band, the fundamental 802.11 MAC and PHY architecture remains similar to Wi-Fi 6 (5 GHz/2.4 GHz)—just adapted to new spectrum rules and features.

High-Level Protocol Stack Diagram

+---------------------------------------------------+
|                   Applications                    |
|          (HTTP, VoIP, Video Streaming, ...)       |
+---------------------------------------------------+
|         Transport Layer (TCP/UDP/QUIC, etc.)      |
+---------------------------------------------------+
|                Network Layer (IP)                |
+---------------------------------------------------+
|       LLC (Logical Link Control - 802.2)          |
+---------------------------------------------------+
|       MAC Sublayer (IEEE 802.11)                  |
|   (Data/Management Frames, CSMA/CA, Security,     |
|        QoS, OFDMA scheduling at MAC level)        |
+---------------------------------------------------+
|       PHY Layer (IEEE 802.11ax in 6 GHz)          |
|  (Modulation, Coding, OFDMA, MU-MIMO, Beamforming)|
+---------------------------------------------------+

Note:

  • Wi-Fi 6E uses the 802.11ax standard but in the newly allocated 6 GHz band (5.925–7.125 GHz in many regions).
  • The diagram above shows the typical OSI layering for a Wi-Fi device (station or AP). Both ends (STA and AP) generally have the same layered stack, with roles differing in association/authentication control.

Layer-by-Layer Responsibilities

1. Application Layer

  • What it does: Runs user applications and services (e.g., web browsing, streaming, VoIP).
  • Wi-Fi Consideration: Data generated here eventually needs reliable or best-effort transmission over the IP layer, then encapsulated into 802.11 frames.

2. Transport Layer (TCP/UDP/QUIC)

  • What it does: Handles end-to-end data flow control and error recovery (TCP) or best-effort delivery (UDP). QUIC runs on top of UDP for modern web transport.
  • Wi-Fi Consideration: Congestion control and retransmissions here operate end-to-end. However, Wi-Fi’s MAC can also do its own frame-level retransmissions, so efficient interplay with TCP is important for overall performance.

3. Network Layer (IP)

  • What it does: Manages logical addressing and routing of packets (IPv4 or IPv6).
  • Wi-Fi Consideration: From the network’s perspective, the Wi-Fi link is just another Layer 2 hop; however, the Wi-Fi MAC must seamlessly carry IP packets, sometimes bridging or NATing at the AP.

4. LLC (Logical Link Control - 802.2)

  • What it does: Sits between MAC and Network layers, providing a common interface and optionally multiplexing protocols (EtherType).
  • Wi-Fi Consideration: In most modern Wi-Fi implementations, LLC overhead is minimal but still formally part of the 802.11 architecture.

5. MAC Sublayer (IEEE 802.11)

  • What it does:

    • Channel Access: Uses CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) to avoid collisions on the shared medium.
    • Frame Exchange: Manages Data frames, Management frames (beacons, probes, association requests/responses), and Control frames (ACK, RTS/CTS).
    • Security: Implements WPA2/WPA3 encryption and authentication (EAP/802.1X or PSK), handling the handshake and key derivation.
    • QoS and Scheduling: With 802.11ax (Wi-Fi 6/6E), includes OFDMA scheduling at the MAC level, BSS coloring, TWT (Target Wake Time) for power saving, and MU-MIMO resource management.
    • Aggregation: Frames can be aggregated (A-MPDU/A-MSDU) to improve efficiency and reduce overhead.

  • Wi-Fi 6E-Specific Considerations:

    • Must comply with 6 GHz regulatory rules, which often distinguish Low Power Indoor (LPI) from Standard Power (with Automated Frequency Coordination, AFC).
    • Additional channels and reduced interference (since 6 GHz is less crowded) can significantly improve throughput and reduce congestion.

6. PHY Layer (IEEE 802.11ax in 6 GHz)

  • What it does:

    • Physical Modulation & Coding: 802.11ax uses OFDM (Orthogonal Frequency-Division Multiplexing), OFDMA (multi-user version), and up to 1024-QAM modulation.
    • MU-MIMO & Beamforming: Multi-user MIMO to serve multiple stations simultaneously, plus beamforming to improve signal gain and coverage.
    • Channelization: In 6 GHz, wide channels (e.g., 160 MHz, 320 MHz in the future) are possible.
    • Preamble / Pilots: Coordinates synchronization, channel estimation, and allows for multi-user scheduling.

  • Wi-Fi 6E-Specific Considerations:

    • Larger contiguous bandwidth in 6 GHz (up to 1.2 GHz of spectrum in some regions) yields more available channels.
    • Shorter range than 2.4/5 GHz due to higher frequency (more path loss, less wall penetration).

STA vs. AP Perspective

Although both stations (STAs) (laptops, phones) and the AP (wireless router or enterprise AP) implement the full 802.11 stack, their roles differ, especially at the MAC sublayer:

  1. AP

    • Broadcasts Beacon frames, manages association/authentication requests.
    • Coordinates OFDMA resource allocations (uplink/downlink).
    • Often handles bridging to a wired LAN or upstream gateway (IP routing/NAT).

  2. Station

    • Scans for AP beacons, selects an AP to connect.
    • Requests association and negotiates security keys.
    • Receives resource allocations from the AP for uplink transmissions under OFDMA (or still uses EDCA if not OFDMA-scheduled).

Key Takeaways

  • Wi-Fi 6E expands 802.11ax into the 6 GHz band, but the fundamental MAC/PHY layering is consistent with earlier Wi-Fi generations (just with new features for higher efficiency and more available channels).
  • PHY enhancements: OFDMA, MU-MIMO, wider channels, and advanced modulation schemes for high throughput.
  • MAC enhancements: Efficient scheduling (OFDMA at the MAC), better QoS handling, BSS coloring to mitigate interference, and improved power-saving features (TWT).
  • Upper Layers (LLC, IP, TCP/UDP) remain mostly unchanged; they benefit from the improved throughput and lower latency at Layers 1 and 2.

In essence, the Wi-Fi 6E stack remains faithful to the OSI model but features major upgrades in the MAC/PHY layers to handle new spectrum rules, higher data rates, and more advanced multi-user operations—particularly important in dense environments and emerging high-bandwidth applications.