7 Quality of Service (QoS) Explained

Key Concepts

• QoS Basics
• Classification
• Marking
• Queuing
• Shaping
• Policing
• Congestion Management

1. QoS Basics

Quality of Service (QoS) is a set of technologies and techniques used to manage network traffic and ensure the performance of critical applications. QoS helps prioritize certain types of traffic over others, ensuring that important data gets through even during periods of high network congestion.

Example: Think of QoS as a traffic cop managing the flow of cars on a busy road. Just as a traffic cop ensures that emergency vehicles get through quickly, QoS ensures that critical network traffic is prioritized.

2. Classification

Classification is the process of identifying and categorizing network traffic based on specific criteria such as source IP, destination IP, port number, protocol, and more. Classification is the first step in applying QoS policies to different types of traffic.

Example: Consider classification as sorting mail at a post office. Just as mail is sorted by destination, network traffic is sorted by its characteristics to apply appropriate QoS policies.

3. Marking

Marking involves tagging network packets with specific QoS values, such as Differentiated Services Code Point (DSCP) or IEEE 802.1p, to indicate their priority. Marking helps routers and switches determine how to handle the traffic based on its priority.

Example: Think of marking as labeling packages with priority tags. Just as priority tags help delivery services handle packages more efficiently, marking helps network devices prioritize traffic.

4. Queuing

Queuing is the process of organizing and managing network packets in different queues based on their priority. Different queuing algorithms, such as FIFO (First In, First Out), PQ (Priority Queuing), and WFQ (Weighted Fair Queuing), determine how packets are processed and transmitted.

Example: Consider queuing as a line at a grocery store. Just as customers in a priority line get served first, packets in a high-priority queue get transmitted before those in lower-priority queues.

5. Shaping

Shaping is a technique used to control the rate at which traffic is sent onto the network. By delaying packets, shaping ensures that the traffic does not exceed a specified rate, helping to prevent congestion and maintain network performance.

Example: Think of shaping as a traffic light that regulates the flow of cars. Just as a traffic light prevents too many cars from entering an intersection at once, shaping prevents too much traffic from overwhelming the network.

6. Policing

Policing is a technique used to enforce QoS policies by monitoring the traffic and ensuring it does not exceed a specified rate. If traffic exceeds the allowed rate, packets may be dropped or marked down to a lower priority.

Example: Consider policing as a speed limit enforcement. Just as a police officer issues tickets to speeders, policing enforces QoS policies by managing traffic that exceeds the allowed rate.

7. Congestion Management

Congestion management involves techniques to handle network congestion, such as Random Early Detection (RED) and Weighted RED (WRED). These techniques help prevent congestion by dropping packets before the network becomes overloaded, ensuring smoother network performance.

Example: Think of congestion management as crowd control at a concert. Just as security personnel manage the flow of people to prevent overcrowding, congestion management techniques prevent network overload by managing traffic flow.