802.11g & e Presenter : Milk

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

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

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

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

Different WLAN system characteristics a802.11b802.11g Operating frequencies 5 GHz U-NII Band 2.4 GHz ISM Band 2.4 GHz ISM Band Modulation techniques OFDMBarker Code / CCK Barker Code / CCK / OFDM Data rates (Mbps) 6,9,12,18,24, 36,48,54 1,2,5.5,111,2,5.5,11, 6,9,12,18,24,36, 48,54 PreambleOFDMLong Short (optional) Long / Short / OFDM CWmin / 31 Slot time9 us20 us20us / 9us (optional)

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

802.11g & b co-exist Many legacy b devices cannot detect the ERP-OFDM signals and it can result in collisions between b and g stations. The g 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

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

QoS Limitations of g  Overview of g  g & b co-exist QoS Limitations of e  Overview of e  EDCA  HCCA  DLP  Block Acknowledgement

QoS Limitations of 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

Beacon delay example TBTT TBTT - target beacon transmission time

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

Overview of e 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)

Major Enhancements in e 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)

Traffic Differentiation

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

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)

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

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

ACCWminCWMax AC_BKaCWminaCWmax AC_BEaCWminaCWmax AC_VI(aCWmin+1)/2 -1aCWmin AC_VO(aCWmin+1)/4 -1(aCWmin+1)/2 -1

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

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

Multiple backoff of MSDU streams with different priorities

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

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

802.11e Superframe

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

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

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.

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

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

Procedure of Block Ack

Immediate Block Ack

Delayed Block Ack