SWRU423A July 2015 – May 2016 WL1801MOD , WL1805MOD , WL1807MOD , WL1831MOD , WL1835MOD , WL1837MOD
The purpose of WLAN QoS is to allow different types of traffic (voice, video, or normal traffic) to have different priorities when approaching the air (trying to send a frame).
The WiLink8 device supports the enhanced distributed channel access (EDCA) QoS. With EDCA, high-priority traffic has a higher chance of being sent than low-priority traffic. On average, a station with high-priority traffic waits less time before it sends its packet than a station with low-priority traffic.
The levels of priority in EDCA are called access categories (ACs). The contention window (CW) can be set according to the traffic expected in each access category, with a wider window needed for categories with heavier traffic. The CWmin and CWmax values are calculated from aCWmin and aCWmax values, respectively, that are defined for each physical layer supported by 802.11e.
EDCA provide four different ACs (from lowest to highest priority):
The WiLink8 devices (STA and AP) support the EDCA in both software and hardware: while the software maintains the different AC queues, the hardware runs the “Air Approach” in real-time competition.
Table 9 shows the default EDCA parameters.
AC | CWmin | CWmax | AIFSN | Max TXOP |
---|---|---|---|---|
Background (AC_BK) | 15 | 1023 | 7 | 0 |
Best Effort (AC_BE) | 15 | 1023 | 3 | 0 |
Video (AC_VI) | 7 | 15 | 2 | 3.008 ms |
Voice (AC_VO) | 3 | 7 | 2 | 1.504 ms |
The actual EDCA parameters are published by the AP side. When running a WiLink8 device as an AP role, you can configure the EDCA parameters in the TI configuration file. There is no option to disable QoS from the STA role (enabled by default), but there is an option in the hostapd.conf file to disable the QoS.
A frame is handled as a QoS frame only if it arrived from the network with QoS information. Each frame without QoS information is handled as a non-QoS frame. The default parameters of non-QoS frames are the same as best-effort frames (that is also the case when the AP does not support QoS).
The EDCA QoS is compatible with the Wi-Fi Alliance WMM Certification, with a small modification. WMM defines eight different TIDs (Traffic ID 0-7), while each traffic ID (TID) gets a specific AC handling.
In a WiLink8 solution, each TID is automatically assigned to its correlated AC (see Table 10).
TID | AC |
---|---|
0 | AC_BE |
1 | AC_BK |
2 | AC_BK |
3 | AC_BE |
4 | AC_VI |
5 | AC_VI |
6 | AC_VO |
7 | AC_VO |
WiLink8.0 devices are fully compliant with Wi-Fi Alliance WMM requirements.