5.2 Wireless LAN QoS

Quality of Service (QoS) in Wireless LANs (WLANs) is crucial for ensuring that critical applications receive the necessary bandwidth and performance. This section will explore key concepts related to WLAN QoS, providing detailed explanations and practical examples to enhance your understanding.

Key Concepts

• Classification and Marking: Identifying and tagging traffic based on its priority.
• Policing and Shaping: Controlling the rate of traffic to ensure it does not exceed specified limits.
• Queuing and Scheduling: Managing the order and priority of traffic in the network.
• Admission Control: Ensuring that the network can handle the requested QoS levels.
• Congestion Management: Handling network congestion to maintain performance.

Detailed Explanation

Classification and Marking

Classification and marking involve identifying network traffic based on specific criteria, such as source IP, destination IP, or application type, and then tagging it with a priority level. This ensures that high-priority traffic, like VoIP or video conferencing, is treated differently from lower-priority traffic, such as email.

Example: In a corporate network, traffic from the VoIP application is classified and marked with a high priority (e.g., DSCP EF). This ensures that VoIP calls receive the necessary bandwidth and low latency, providing a consistent communication experience.

Policing and Shaping

Policing and shaping control the rate of traffic to ensure it does not exceed specified limits. Policing drops excess traffic, while shaping buffers excess traffic and releases it at a controlled rate. This helps maintain network performance and prevents congestion.

Example: A university network uses policing to limit the bandwidth for peer-to-peer file sharing applications. Excess traffic is dropped, ensuring that critical academic applications have sufficient bandwidth.

Queuing and Scheduling

Queuing and scheduling manage the order and priority of traffic in the network. Different queuing algorithms, such as Weighted Fair Queuing (WFQ) or Priority Queuing (PQ), determine how traffic is processed. This ensures that high-priority traffic is processed first, maintaining performance for critical applications.

Example: In a hospital, Priority Queuing is used to ensure that patient monitoring data is processed before other network traffic. This guarantees that patient data is transmitted promptly, maintaining patient safety.

Admission Control

Admission control ensures that the network can handle the requested QoS levels. It evaluates the network's capacity and decides whether to admit or deny new traffic based on available resources. This prevents overloading the network and ensures that existing traffic maintains its QoS levels.

Example: A financial institution uses admission control to manage video conferencing sessions. If the network is already handling a high volume of critical transactions, new video conferencing sessions may be denied to prevent network congestion.

Congestion Management

Congestion management involves handling network congestion to maintain performance. Techniques such as Random Early Detection (RED) or Weighted RED (WRED) monitor the queue length and drop packets before the queue becomes full. This helps prevent congestion and ensures that high-priority traffic is not affected.

Example: In a large office, WRED is used to manage network congestion during peak hours. Packets are dropped based on their priority, ensuring that critical business applications continue to perform well even when the network is busy.

By understanding and implementing these concepts, you can effectively manage QoS in your Wireless LAN, ensuring optimal performance for critical applications and a reliable network experience for all users.