Operation Manual

VigorAP 910C User’s Guide
165
Download Limit
Define the maximum speed of the data downloading which will
be used for the wireless station connecting to VigorAP with the
same SSID.
Use the drop down list to choose the rate. If you choose User
defined, you have to specify the rate manually.
Auto Adjustment
Check this box to have the bandwidth limit determined by the
system automatically.
Total Upload Limit
When Auto Adjustment is checked, the value defined here will
be treated as the total bandwidth shared by all of the wireless
stations with the same SSID for data uploading.
Total Download
Limit
When Auto Adjustment is checked, the value defined here will
be treated as the total bandwidth shared by all of the wireless
stations with the same SSID for data downloading.
After finishing this web page configuration, please click OK to save the settings.
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Airtime fairness is essential in wireless networks that must support critical enterprise
applications.
Most of the applications are either symmetric or require more downlink than uplink capacity;
telephony and email send the same amount of data in each direction, while video streaming
and web surfing involve more traffic sent from access points to clients than the other way
around. This is essential for ensuring predictable performance and quality-of-service, as well
as allowing 802.11n and legacy clients to coexist on the same network. Without airtime
fairness, offices using mixed mode networks risk having legacy clients slow down the entire
network or letting the fastest client(s) crowd out other users.
With airtime fairness, every client at a given quality-of-service level has equal access to the
network's airtime.
The wireless channel can be accessed by only one wireless station at the same time.
The principle behind the IEEE802.11 channel access mechanisms is that each station has
equal probability to access the channel. When wireless stations have similar data rate, this
principle leads to a fair result. In this case, stations get similar channel access time which is
called airtime.
However, when stations have various data rate (e.g., 11g, 11n), the result is not fair. The
slow stations (11g) work in their slow data rate and occupy too much airtime, whereas the
fast stations (11n) become much slower.
Take the following figure as an example, both Station A(11g) and Station B(11n) transmit
data packets through VigorAP 910C. Although they have equal probability to access the
wireless channel, Station B(11n) gets only a little airtime and waits too much because Station
A(11g) spends longer time to send one packet. In other words, Station B(fast rate) is
obstructed by Station A(slow rate).