Cisco Cisco Aironet 3700i Access Point Libro bianco
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The next step is to apply the newly created Air Time Fairness policy to: all access points; a select group of access
points; or to an single access point in a given WLAN (SSID). This step effectively assigns an SSID to a time slice. It
is worthwhile to note that multiple SSIDs can be assigned to the same time slice.
However, this generally assumes a single customer requires multiple SSIDs for some business-related reason.
Furthermore, an access point can support multiple WLANs with multiple policies. Policies set in individual access
point and access point group configurations always override per-global network policies.
All traffic from a given SSID utilizes the assigned time slice for transmissions. Downlink traffic destined for different
SSIDs will share the same time slice, and will share it in a first-come-first-served manner.
Next, consider a potential scenario that uses this mechanism (Figure 3). Assume a public Wi-Fi venue exists,
where the venue WLAN provides services for itself and also for two service providers who lease the WLAN.
The network administrator assigns Time Slice 1 to the venue owner and assigns 10 percent of the available airtime
to Time Slice 1. SSID 1 uses Time Slice 1 for the venue owner.
Next, the network administrator assigns Time Slice 2 to Service Provider A and assigns 45 percent of the available
airtime to Time Slice 2. Note that Time Slice 2 could support two different networks (SSIDs) for Service Provider A.
In this example, the SSIDs A_Network_1 and A_Network_2 both share Time Slice 2 since Service Provider A is
leasing 45 percent of the available airtime.
Finally, the network administrator assigns Time Slice 3 to Service Provider B and assigns 45 percent of the
available airtime to Time Slice 3. Time Slice 3 could also support two different networks (SSIDs) for Service
Provider B. In this example, the SSIDs B_Network_1 and B_Network_2 both share Time Slice 3 since Service
Provider B is leasing 45 percent of the available airtime.
Figure 3. SSID Example
What the Air Time Fairness Solution Is Not
Before explaining Air Time Fairness in further detail, note that the solution does not replace Enhanced Distributed
Channel Access (EDCA). Instead, it is applied in conjunction with EDCA. In the downlink direction, the queues that
feed the EDCA output buffers are serviced in such a way to permit airtime to be distributed or allocated unequally
per group. The queues are based on the types of users, devices, etc., instead of allowing only traffic patterns to
determine medium access time.