QoS Overview

Traditional QoS (Quality of Service) methods separate client traffic into queues based on traffic type, and then schedule the transmission of the traffic based on data rates from the queues (128 Kbps, for example). In a WLAN, this means that a slower client (802.11b) uses significantly more airtime to transmit the same amount of data as a much faster client (802.11ax). To address this and make airtime access more equitable, Extreme Networks provides airtime-based QoS. Instead of using just bandwidth in the QoS calculations, APs allocate airtime per client, per traffic class, and per user profile by dynamically calculating airtime consumption per packet. When multiple client types (802.11a, ac, b, g, n or ax) are active in the same WLAN, all clients receive the same amount of airtime (10 ms for example), regardless of the client type. An 11ax client might be able to send 128 Kbps of traffic in the allocated slot, while an 11b client might only send 50 Kbps, but both clients receive the same amount of airtime.

A visual representation of the difference between bandwidth-based scheduling and airtime-based scheduling when two clients are transmitting at different data rates looks like this:

Dashes ( — ) indicate airtime for frames transmitted at a low data rate.

Bullets ( • ) indicate airtime for frames transmitted at a high data rate.

The faster client might be using 802.11ax and the slower client 802.11 a, b, g, or n, or they might both be using the same protocol, but one is farther away and must use a slower speed than the other.

With bandwidth-based scheduling, both the slow and fast clients finish at the same time regardless of their data rates, and they compete the entire time for the air. Because both clients have an equal opportunity to transmit frames, the faster client's throughput slows down to the rate of the slower client.

With Dynamic Airtime Scheduling, both clients get their proportion of airtime. The faster client finishes four times faster, and the slower client finishes at the same time as it did with bandwidth-based scheduling. The fast client is rewarded, and the slow client is not penalized.

Note

QoS rate control and queuing functionality on Extreme Networks routers applies to traffic from the LAN to the WAN, but not in the reverse direction. This is primarily because bandwidth on the WAN interface is typically much less than that on the LAN interfaces. On the other hand, Extreme Networks APs apply QoS rate control and queuing to both outbound and inbound traffic. They perform data rate limiting on incoming Ethernet and Wi-Fi interfaces, and they queue packets on outgoing Wi-Fi interfaces. APs do not queue any packets that they send out their Ethernet interfaces because the Ethernet link is not a point of congestion; however, they do set the 802.1p or DSCP priority in the packet headers as defined in the marker map so that the next-hop router can perform QoS queuing.

The benefits of Dynamic Airtime Scheduling include:

Per User Rate Limit (802.11a): The maximum amount of bandwidth in Kbps (kilobits per second) that an individual member of this profile can use when connecting to an Extreme Networks device supporting the IEEE 802.11a standard. The default setting is 54000 Kbps, or 54 Mbps, which is the maximum data rate for 802.11a.

Per User Rate Limit (802.11n/a): The maximum amount of bandwidth in Kbps that an individual member of this profile can use when connecting to an Extreme Networks device supporting the IEEE 802.11n/a standards. The default setting is 1000000 Kbps, or 1 Gbps, which is well beyond the most aggressive data rates for 802.11n (600 Mbps with four spatial streams) and 802.11a (54 Mbps).

Per User Rate Limit (802.11ac): The maximum amount of bandwidth in Kbps that an individual member of this profile can use when connecting to an Extreme Networks device supporting the IEEE 802.11ac standard. The default setting is 2000000 Kbps, or 2 Gbps, which accommodates an 802.11ac device using MCS 6 or 7 with three spatial streams or MSC 8 or 9 with two spatial streams.

Per User Rate Limit (802.11b/g): The maximum amount of bandwidth in Kbps (kilobits per second) that an individual member of this profile can use when connecting to an Extreme Networks device supporting IEEE 802.11b/g standards. The default setting is 54000 Kbps, or 54 Mbps, which is the maximum data rate for 802.11g, and easily accommodates the 11 Mpbs data rate of 802.11b.

Per User Rate Limit (802.11g/n): The maximum amount of bandwidth in Kbps that an individual member of this profile can use when connecting to an Extreme device supporting the IEEE 802.11n standard. The default setting is 1000000 Kbps, or 1 Gbps, which outstrips the most aggressive data rates of 802.11n (600 Mbps with four spatial streams).

Scheduling Weight: The scheduling weight defines a preference for forwarding traffic using a WRR (weighted round robin) scheduling discipline. The weight for one class of traffic is relative to the weights of other classes. A larger weight of one traffic class indicates a greater preference in relation to the weights of other classes. For example, if you use weights to give the forwarding of one class of traffic twice as much priority as another, the effect of weights 5 to 10 would be the same as 50 to 100 (where 10 and 100 weigh more than 5 and 50 respectively and, therefore, indicate greater preferences).

Weight %: An automatically calculated percentage of the weight of each class of traffic in relation to the weights of other classes.