Cisco Cisco Aironet 3700i Access Point 백서

 

 

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In this case, a university shares a WLAN between students, faculty, and guests. The guest network can be further 

partitioned by the service provider. Each group can be assigned a percentage of airtime. 

In these areas, the venue shares a WLAN between employees and guests. The service provider can further 

partition the guest network. Guests could be sub-grouped by tier of service type, with each subgroup assigned a 

percentage of airtime. For example, a paid group can be entitled to more airtime than a free group. 

In this case, the business entity managing the hotspot, whether a service provider or an enterprise, can allocate 

and subsequently lease airtime to other business entities. 

Cisco Air Time Fairness - Basic Concepts and Goals 

The easiest way to envision Air Time Fairness is that it provides the ability to both monitor and manage the amount 

of time on the air on a per-client, per-SSID, or per-other basis. (This paper will discuss the per-other category after 

an overview of the fundamental concepts.) The effect is to control the amount of traffic a client or SSID is sending 

into the WLAN and receiving from the WLAN at any given time. 

In other words, the primary goal of Air Time Fairness is to help avoid any one client or SSID from occupying an 

unfair amount of Wi-Fi airtime on a particular channel (for instance, on a given access point or radio). In 

accomplishing this, Air Time Fairness also provides a customer with the ability to define what fairness means within 

their environment with regard to the amount of on-airtime and the amount of the traffic that can be sent in any given 

time period. 

Because airtime is itself managed and is a shared resource, airtime rate-limiting and policing applies to the sum of 

downlink and uplink airtime. 

In summary, the goals of Air Time Fairness are to: 

1.  Provide the ability to allocate medium access as a percentage of available airtime instead of a specific bit rate 

2.  Make this ability available on a per-client, per-SSID, and per-other basis 

3.  Apply to all packets that go over the air, and not just data frame payload types (for example, Transmission 

Control Protocol [TCP] or User Datagram Protocol [UDP]) 

4.  Apply to all clients, independent of type or current status (for instance, data rate, signal strength, etc.) 

Although rate limiting controls throughput, it cannot control airtime. Policing bandwidth (capacity in bits per second 

[bps]) is not an efficient way to allocate Wi-Fi airtime. This is because clients connect at different speeds, 

depending on the RF link conditions between the access point and the client. Therefore, the overall capacity, being 

managed by a fixed-bandwidth rate limit, is dynamic. This means either we underuse the WLAN (rate limits are too 

restrictive) or overuse the WLAN (rate limits are too liberal). Furthermore, packet errors lead to retransmissions (to 

avoid packet loss), which consume additional airtime and are not accounted for in rate limiting.