Quality of Service, Dynamic Rate Switching, and Backward Compatibility

As wireless technology evolves, new features and functionalities are introduced to improve network performance and user experience on Wireless LANs (WLANs). In this tutorial, I’ll cover three important concepts that play a significant role in modern WLAN environments: Quality of Service (QoS), Dynamic Rate Switching (DRS), and Backward Compatibility. Understanding these features enables network administrators to optimize network performance and ensure compatibility across various devices.

1. Quality of Service (QoS) in Wireless LANs

Quality of Service (QoS) is crucial in prioritizing traffic that is sensitive to delays, such as VoIP (Voice over IP) calls or streaming video. In a wireless environment, some types of data, like voice and video, need to be transmitted immediately because they are highly sensitive to latency. Delays can disrupt these services, resulting in poor call quality, buffering, or video stuttering.

While QoS is a well-established concept in wired networks, it functions differently in wireless networks due to the nature of wireless communication. Wireless LANs operate in a half-duplex mode, meaning that only one device can transmit data at a time. If a device is transmitting data, other devices must wait until the channel is clear to start their own transmissions. This fundamental aspect of wireless communication can introduce latency and affect overall network performance.

How QoS Works in Wireless LANs

In a WLAN environment, QoS prioritizes traffic by adjusting the “wait time” for certain types of packets. Devices with higher priority data have a shorter initial wait time before they are allowed to transmit. Let’s take the example of a VoIP phone on a WLAN. When QoS is enabled, this phone’s wait time before it can access the network is reduced. As a result, it can begin transmitting data faster than other devices that don’t have priority.

For instance, consider a wireless network where devices typically wait for 15 milliseconds before accessing the medium. When QoS is applied to a VoIP phone, the wait time for this device might be reduced to just 3 milliseconds. This priority wait time adjustment allows the VoIP phone to send data faster, reducing latency and ensuring smoother voice communication.

This prioritization is especially helpful in environments with many devices, where delays can accumulate quickly due to network congestion. By setting priority levels, administrators can ensure that latency-sensitive applications like VoIP and video conferencing are less affected by congestion, maintaining a high-quality user experience.