Making Wi-Fi Faster: How Block ACK Speeds Up Your Connection

Wi-Fi WiMax
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:small_blue_diamond: What Is Block Acknowledgment (Block ACK)?

Imagine sending 10 packages through the mail and getting 10 separate delivery receipts—tedious, right? With Block ACK, Wi-Fi bundles acknowledgments for a whole batch of frames into one “block” ACK, slashing control-frame overhead and supercharging throughput. :rocket:

:scroll: Evolution in Wi-Fi Standards

  • 802.11e (2005): Introduced Block ACK as an optional QoS enhancement.

  • 802.11n (2009): Made Block ACK mandatory for all HT (High-Throughput) devices and added Compressed & Multi-TID variants.

  • 802.11ax/11be: Further refined HE Block ACK for better efficiency in OFDMA and Multi-Link Operation.

:arrows_counterclockwise: How It Works: Message Flow

  1. ADDBA Exchange
    ADDBA Request: Initiator checks peer’s Block ACK capability, negotiates
    buffer size & policy.

ADDBA Response: Responder accepts, establishing the Block ACK session.

  1. Burst Transmission
    Transmitter sends multiple QoS-tagged MPDUs back-to-back within a TXOP
    or via EDCA.

  2. BLOCKACKREQ → BLOCKACK
    Transmitter sends a BlockAckReq.
    Receiver returns a bitmap marking which frames arrived intact.

  3. Selective Retransmissions
    Only missing MPDUs are resent—no per-frame ACK overhead.

  4. DELBA Teardown
    DELBA frames release session resources when traffic ends or on timeout.

:zap: Why It Matters: Impact & Benefits

  • Fewer Control Frames → Up to 60–70% reduction in ACK traffic
  • Lower Latency → Less contention in crowded RF environments
  • Higher Throughput → Ideal for video, AR/VR, large file transfers & bursty IoT

:factory: Real-World Use Cases

  • Live Video Surveillance: Consolidated ACKs minimize retransmission delays.

  • AR/VR Experiences: Keeps MAC overhead low to maintain sub-20 ms latency.

  • Bulk File Transfers: Large data blocks traverse the network with fewer handshakes.

  • Industrial IoT: Periodic sensor bursts preserve airtime & device battery life.

:bulb: Additional Insights & Best Practices

  • Tune Block Size & Timeout: Larger buffers boost efficiency but require more memory—find the sweet spot.

  • Use Compressed Block ACK: Saves airtime by sending only the necessary bitmap bits.

  • Leverage Multi-TID Sessions: Aggregate traffic from multiple priorities (voice, video, data) in one stream.

  • Monitor Error Rates: In very lossy links, too-large blocks can lead to retransmission storms—scale block sizes down.

  • Explore HE Enhancements: In 802.11ax/be, Block ACK pairs beautifully with OFDMA & Multi-Link to maximize channel utilization.

See It in Action
I’ll be sharing wireless sniffer logs (Wireshark captures).

Add Block Ack Request

Add Block Ack Request
Add Block Ack Request1075Ă—430 88.4 KB

Add Block Ack Response

Add Block Ack Response
Add Block Ack Response1066Ă—452 88.4 KB

Block Ack

Block Ack
Block Ack1069Ă—384 109 KB

LinkedIn: :point_down:

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Thanks for sharing!

Apart from what you have said, we also have BA bitmap size increase from the initial days of 64-bit BA.

We now have 64, 128, 256, 512, and 1024 BA possibilities. Many devices now support atleast 256 bit BA and some support 1024 BA.

A nice exposition of 1024 BA has been done by Gjermund Raaen here at :point_right: https://www.youtube.com/watch?v=rk2aimstNdE

I always say that A-MPDUs with BA is one of the key technologies behind HT, VHT, and EHT throughput numbers…

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