QoS with EDCA Downgrading November 2009 doc.: IEEE 802.11-yy/xxxxr0 November 2009 QoS with EDCA Downgrading Date: 2009-11-19 Author: Dave Stephenson, Cisco John Doe, Some Company

November 2009 doc.: IEEE 802.11-yy/xxxxr0 November 2009 Abstract This presentation describes the behavior in IEEE 802.11-2007 dubbed “EDCA Downgrading” and its effect on managing QoS using admission control in an ESS Dave Stephenson, Cisco John Doe, Some Company

What is “EDCA Downgrading” November 2009 doc.: IEEE 802.11-yy/xxxxr0 November 2009 What is “EDCA Downgrading” EDCA downgrading is the behavior in which a STA transmits un-admitted traffic from a queue requiring admission control whose EDCAF uses the EDCA parameters from a lower queue not requiring admission control Definitions: un-admitted traffic: traffic which has not been admitted via an ADDTS request that’s transmitted on an AC configured for mandatory admission control EDCA uses a fixed UP to AC mapping (Table 9-1) Example: QoS AP designates AC_VO as requiring admission control (ACM=1) non-AP QoS STA does not have admitted TSPEC for UP=6, but frame is transmitted from AC_VO queue having TID in qos_control field set to 6 AC_VO’s EDCAF uses AC_BE’s EDCA parameters (AIFSN, CWmin, CWmax) Dave Stephenson, Cisco John Doe, Some Company

Managing QoS via Admission Control November 2009 doc.: IEEE 802.11-yy/xxxxr0 November 2009 Managing QoS via Admission Control Admission control effectively manages QoS by enforcing an upper limit on the offered load of prioritized traffic transmitted on a channel Each STA is permitted to use a metered portion of the available medium time on a channel An AP measures and maintains a record of channel medium time usage per access category Frames transmitted using AC_VO, AC_VI and AC_BE EDCA parameters Frames transmitted by non-AP QoS STAs associated to the QoS AP Frames transmitted by co-channel QoS APs and STAs An AP admits/denies each ADDTS Request by comparing channel usage to its internal threshold for that AC An AP (in promiscuous mode) accounts for traffic according to the TID in the received frame The EDCA parameters used by transmitter are inferred from the TID—EDCA downgrading breaks the TID:EDCA parameter binding Dave Stephenson, Cisco John Doe, Some Company

A QoS AP Shouldn’t use EDCA Downgrading November 2009 doc.: IEEE 802.11-yy/xxxxr0 November 2009 A QoS AP Shouldn’t use EDCA Downgrading EDCA downgrading causes head-of-line blocking Example: frame belonging to un-admitted TS reaches the front of AP’s AC_VO queue and is transmitted using AC_BE’s EDCA parameters Frames belonging to admitted TSs also enqueued in AC_VO and destined to other non-AP QoS STAs must suffer access delay to medium imposed by AC_BE queuing parameters Possible QoS DoS attack if non-AP QoS STA sets up un-admitted high datarate downstream flow—repetitive head-of-line blocking QoS DoS attack also possible with U-APSD operation Dave Stephenson, Cisco John Doe, Some Company

November 2009 doc.: IEEE 802.11-yy/xxxxr0 November 2009 Breakage of U-APSD non-AP STA may have expectation that a bi-directional TS will have the same UP used for downstream frames and upstream frames If both QoS AP and non-AP QoS STA use EDCA downgrading, then U-APSD still works properly With same value of UP in both downstream and upstream direction, non-AP QoS STA can properly configure U-APSD trigger and delivery enabled queuing If (layer above MAC) in QoS AP re-marks UP to avoid head-of-line blocking, then U-APSD breaks Downstream frame won’t be enqueued in “expected” AC Dave Stephenson, Cisco John Doe, Some Company

November 2009 doc.: IEEE 802.11-yy/xxxxr0 November 2009 Recommendation Add MIB variable dot11RejectUnadmittedTraffic which causes MA-UNITDATA primitive to reject unadmitted traffic and return a status code in MA-UNITDATA.confirm Layer above MAC can change priority in subsequent MA-UNITDATA.request Dave Stephenson, Cisco John Doe, Some Company