802.11g & 802.11e
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Transcript of 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 802.11g & 802.11b co-exist
QoS Limitations of 802.11 802.11e
Overview of 802.11e EDCA HCCA DLP Block Acknowledgement
Overview of 802.11g
Provide high data ratesBackward compatibility with legacy 802.11
and 802.11b devicesThe new features of 802.11g
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
802.11a 802.11b 802.11g
Operating
frequencies
5 GHz U-NII
Band
2.4 GHz ISM
Band
2.4 GHz ISM
Band
Modulation
techniques
OFDM Barker Code
/ CCK
Barker Code
/ CCK / OFDM
Data rates
(Mbps)
6,9,12,18,24,
36,48,54
1,2,5.5,11 1,2,5.5,11,
6,9,12,18,24,36,
48,54
Preamble OFDM Long
Short (optional)
Long / Short /
OFDM
CWmin 15 31 15 / 31
Slot time 9 us 20 us 20us /
9us (optional)
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
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
Protection Mechanisms
sender
receiver
Non-ERPCTS
ERP-OFDMdata
sender
receiver
Non-ERPRTS
Non-ERPCTS
ERP-OFDMdata
RTS/CTS
CTS to Self
ERP-OFDMACK
ERP-OFDMACK
RTS NAV
CTS NAV
CTS NAV
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
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 requirem
ent of traffic
Beacon delay example
TBTTTBTT
TBTT - target beacon transmission time
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
Overview of 802.11e
Support QoS in WLANBackwardly compatible with the DCF and
PCFHybrid Coordination Function (HCF) acce
ss method is added, including Contention-Based channel access
Enhanced Distributed Channel Access (EDCA) Controlled channel access
HCF Controlled Channel Access (HCCA)
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)
Traffic Differentiation
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
EDCA
Difference from original DCF Contention between ACs (Not STAs) New Inter-frame Space (IFS) for each AC: Arbitr
ation 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 fra
me containing “EDCA Parameter Set” element
DIFS = 2 x aSlotTime+ aSIFSTime
AC CWmin CWMax
AC_BK aCWmin aCWmax
AC_BE aCWmin aCWmax
AC_VI (aCWmin+1)/2 -1 aCWmin
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 withdifferent priorities
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
HCF Controlled Channel Access (HCCA)
The procedure is similar to PCFHybrid 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
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
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
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
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