802.11bn Packet Formats ========================== .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **1. What is the general structure of an 802.11b/n (bn) packet?** Both 802.11b and 802.11n packets include a MAC header, payload (data), and Frame Check Sequence (FCS). 802.11n may also include HT-specific enhancements and frame aggregation. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **2. What are the key differences between 802.11b and 802.11n packet formats?** 802.11n supports MIMO, frame aggregation (A-MPDU, A-MSDU), HT Control fields, and operates on both 2.4 GHz and 5 GHz. 802.11b only supports DSSS/CCK and 2.4 GHz band. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **3. How does the preamble differ in 802.11b and 802.11n?** 802.11b uses short or long preambles. 802.11n uses mixed-mode or Greenfield preambles, with mixed-mode being backward compatible with 802.11b. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **4. What is the role of the PLCP header in 802.11b/n?** The PLCP (Physical Layer Convergence Protocol) header informs the receiver about the modulation scheme, rate, and length of the frame. It differs between b and n standards due to modulation differences. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **5. What is A-MPDU in 802.11n?** A-MPDU (Aggregated MAC Protocol Data Unit) allows multiple MPDUs to be sent as one PHY-layer transmission, improving efficiency and reducing overhead. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **6. What is A-MSDU in 802.11n?** A-MSDU (Aggregated MAC Service Data Unit) combines multiple MSDUs into a single MPDU at the MAC layer, reducing per-frame overhead. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **7. How does 802.11n improve efficiency compared to 802.11b?** Through MIMO, wider channels (40 MHz), frame aggregation, and block acknowledgments, 802.11n achieves much higher throughput and better performance than 802.11b. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **8. What types of frames are supported in 802.11b/n?** Both support Management, Control, and Data frames. 802.11n enhances Data frames with support for aggregation and Block ACK. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **9. What is the function of the HT Control field in 802.11n?** The HT Control field is used in beamforming, calibration, and sounding operations. It’s only present in 802.11n and newer standards. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **10. Is 802.11n backward compatible with 802.11b?** Yes, 802.11n supports backward compatibility through mixed-mode operation, allowing it to interoperate with 802.11b/g devices. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **11. What are the typical data rates for 802.11b and 802.11n?** 802.11b supports 1, 2, 5.5, and 11 Mbps. 802.11n supports up to 600 Mbps depending on MIMO configuration and channel bonding. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **12. What is Block ACK in 802.11n?** Block ACK allows multiple frames to be acknowledged at once, reducing control overhead and increasing throughput—unlike 802.11b which uses individual ACKs. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **13. What modulation schemes are used in 802.11b vs 802.11n?** 802.11b uses DSSS and CCK. 802.11n uses OFDM with QPSK, 16-QAM, and 64-QAM, enabling higher spectral efficiency. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **14. What is the maximum packet size supported in 802.11n?** With A-MPDU aggregation, the total size can exceed 64 KB, far larger than typical 802.11b frames, which are limited by smaller MTUs and no aggregation. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **15. Can 802.11n use both 2.4 GHz and 5 GHz?** Yes, 802.11n supports dual-band operation, unlike 802.11b which is limited to 2.4 GHz only. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **16. Do 802.11b/n packets differ in MAC headers?** The base MAC headers are compatible, but 802.11n may include HT-specific fields like HT Control, which are not present in 802.11b. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **17. What is the typical FCS (Frame Check Sequence) size in 802.11b/n?** Both use a 32-bit CRC for the FCS to ensure data integrity. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **18. How does channel bonding work in 802.11n?** 802.11n can combine two 20 MHz channels into a 40 MHz channel, effectively doubling throughput. 802.11b does not support this. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **19. Can 802.11n fall back to 802.11b speeds?** Yes. When needed for compatibility, 802.11n can operate at 802.11b data rates like 11 Mbps. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **20. Why is 802.11n preferred over 802.11b today?** 802.11n offers dramatically higher speeds, better reliability, support for MIMO, and greater efficiency through aggregation and block ACK—making it much more suitable for modern networks. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Topics in this section, * :ref:`Reference links ` .. _packet_formats_step17: .. tab-set:: .. tab-item:: Reference links * Reference links