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802.11g & 802.11e

802.11g & 802.11e. Presenter : Milk. Outline. 802.11g Overview of 802.11g 802.11g & 802.11b co-exist QoS Limitations of 802.11 802.11e Overview of 802.11e EDCA HCCA DLP Block Acknowledgement Admission Control Power Management. 802.11g. 802.11g Overview of 802.11g

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802.11g & 802.11e

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  1. 802.11g & 802.11e Presenter : Milk

  2. Outline • 802.11g • Overview of 802.11g • 802.11g & 802.11b co-exist • QoS Limitations of 802.11 • 802.11e • Overview of 802.11e • EDCA • HCCA • DLP • Block Acknowledgement • Admission Control • Power Management

  3. 802.11g • 802.11g • Overview of 802.11g • 802.11g & 802.11b co-exist • QoS Limitations of 802.11 • 802.11e • Overview of 802.11e • EDCA • HCCA • DLP • Block Acknowledgement

  4. Overview of 802.11g • Provide high data rates • Backward compatibility with legacy 802.11 and 802.11b devices • The new features of 802.11g • The provision of four different physical layers • Protection Mechanisms

  5. 802.11g PHY layers CCK - Complementary code keying OFDM - Orthogonal frequency division multiplexing PBCC - Packet Binary Convolutional Code

  6. Different WLAN system characteristics

  7. 802.11g • 802.11g • Overview of 802.11g • 802.11g & 802.11b co-exist • QoS Limitations of 802.11 • 802.11e • Overview of 802.11e • EDCA • HCCA • DLP • Block Acknowledgement

  8. 802.11g & 802.11b co-exist • Many legacy 802.11b devices cannot detect the ERP-OFDM signals and it can result in collisions between 802.11b and 802.11g stations. • The 802.11g suggests a solution, which is based on the channel reservation for the ERP-OFDM transmissions. • Use RTS/CTS to protect ERP-OFDM • Use CTS-to-Self to protect ERP-OFDM

  9. Protection Mechanisms Non-ERP RTS ERP-OFDM data sender RTS/CTS Non-ERP CTS ERP-OFDM ACK receiver RTS NAV CTS NAV Non-ERP CTS ERP-OFDM data sender CTS to Self ERP-OFDM ACK receiver CTS NAV

  10. QoS Limitations of 802.11 • 802.11g • Overview of 802.11g • 802.11g & 802.11b co-exist • QoS Limitations of 802.11 • 802.11e • Overview of 802.11e • EDCA • HCCA • DLP • Block Acknowledgement

  11. QoS Limitations of 802.11 • DCF (Distributed Coordination Function) • Only support best-effort services • No guarantee in bandwidth, packet delay and jitter • PCF (Point Coordination Function) • Unpredictable beacon frame delay due to incompatible cooperation between CP and CFP modes • Transmission time of the polled stations is unknown • Point Coordinator(PC) does not know the QoS requirement of traffic

  12. Beacon delay example TBTT TBTT TBTT - target beacon transmission time

  13. 802.11e • 802.11g • Overview of 802.11g • 802.11g & 802.11b co-exist • QoS Limitations of 802.11 • 802.11e • Overview of 802.11e • EDCA • HCCA • DLP • Block Acknowledgement

  14. Overview of 802.11e • Support QoS in WLAN • Backwardly compatible with the DCF and PCF • Hybrid Coordination Function (HCF) access method is added, including • Contention-Based channel access • Enhanced Distributed Channel Access (EDCA) • Controlled channel access • HCF Controlled Channel Access (HCCA)

  15. Major Enhancements in 802.11e • Basic elements for QoS • Traffic Differentiation • Concept of Transmission Opportunity (TXOP) • New Contention-based channel access • Enhanced Distributed Channel Access (EDCA) • New Contention-free channel access • HCF Controlled Channel Access (HCCA) • Other new mechanisms for higher throughput • Block Acknowledgement (Block Ack) • Direct Link Protocol (DLP)

  16. Traffic Differentiation

  17. 802.11e • 802.11g • Overview of 802.11g • 802.11g & 802.11b co-exist • QoS Limitations of 802.11 • 802.11e • Overview of 802.11e • EDCA • HCCA • DLP • Block Acknowledgement

  18. EDCA • Difference from original DCF • Contention between ACs (Not STAs) • New Inter-frame Space (IFS) for each AC: Arbitration Inter frame Space (AIFS) • Transmission Opportunity (TXOP)

  19. Access Category (AC) • In EDCA, media access is based on the AC of MSDU • 4 AC’s are defined • AC_BK (background) • AC_BE (best-effort) • AC_VI (Video) • AC_VO (Voice) • In EDCA, the size of Contention-Window (CW) and Inter-frame space (IFS) is dependent on AC

  20. Arbitration Interframe Space (AIFS) • QSTA use AIFS to defer the contention window or transmission for each AC • AIF[AC] = AIFSN[AC]x aSlotTime+ aSIFSTime • AIFSN for each AC is broadcast via beacon frame containing “EDCA Parameter Set” element • DIFS = 2 x aSlotTime+ aSIFSTime

  21. Transmission Opportunity (TXOP) • TXOP: the duration of a QSTA to transmit frame(s) • When will a QSTA get a TXOP ? • Win a contention in EDCA during CP • Receive a CF-poll (“polled TXOP”) from HC

  22. Transmission Opportunity (TXOP) (cont.) • In TXOP, frames exchange sequences are separated by SIFS

  23. Multiple backoff of MSDU streams withdifferent priorities

  24. 802.11e • 802.11g • Overview of 802.11g • 802.11g & 802.11b co-exist • QoS Limitations of 802.11 • 802.11e • Overview of 802.11e • EDCA • HCCA • DLP • Block Acknowledgement

  25. HCF Controlled Channel Access (HCCA) • The procedure is similar to PCF • Hybrid Coordinator (HC) • Operate at QAP • Control the iteration of CFP and CP • By using beacon and CF-End frame and NAV Mechanism (Same as PCF) • Use polling Scheme to assign TXOP to QSTA • Issue CF-poll frame to poll QSTA • Polling can be issued in both CFP & CP

  26. 802.11e Superframe

  27. 802.11e • 802.11g • Overview of 802.11g • 802.11g & 802.11b co-exist • QoS Limitations of 802.11 • 802.11e • Overview of 802.11e • EDCA • HCCA • DLP • Block Acknowledgement

  28. Direct Link Protocol (DLP) • Direct Link • Directly send frames from one QSTA to another in QBSS

  29. The handshake procedure Notes: 1.DLS Request and DLS Response are both Action management frame 2.The direct link will become inactive if no frames have been exchanged for DLPTimeoutValue duration. 3.Recipient shall not go into power save for DLPTimeoutValue duration. 4.After timeout, the frames are transmitted via AP again.

  30. 802.11e • 802.11g • Overview of 802.11g • 802.11g & 802.11b co-exist • QoS Limitations of 802.11 • 802.11e • Overview of 802.11e • EDCA • HCCA • DLP • Block Acknowledgement

  31. Brief of Block Ack • (Optional function in implementation) • Improve channel efficiency • By aggregating several acks into one frame • Two types • Immediate Block Ack • Suitable for High-bandwidth, low latency traffic • Delayed Block Ack • Suitable for applications tolerating moderate latency

  32. Procedure of Block Ack

  33. Immediate Block Ack

  34. Delayed Block Ack

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