7.1 QoS Basics Explained

Key Concepts

• QoS Overview
• Classification
• Marking
• Policing and Shaping
• Queuing

1. QoS Overview

Quality of Service (QoS) is a set of 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 is transmitted efficiently and reliably.

Example: Think of QoS as a traffic cop directing vehicles at a busy intersection. 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 criteria such as source IP, destination IP, protocol, and port number. This helps in determining which type of traffic should be given priority.

Example: Consider classification as sorting mail at a post office. Just as mail is sorted into different categories (letters, packages, express), network traffic is sorted into different categories (voice, video, data) for prioritization.

3. Marking

Marking involves tagging packets with specific identifiers (such as DSCP or 802.1p) to indicate their priority level. This tagging helps network devices apply appropriate QoS policies to the traffic.

Example: Think of marking as labeling boxes with priority tags. Just as priority tags help warehouse workers handle high-priority items first, marking helps network devices prioritize high-priority traffic.

4. Policing and Shaping

Policing and shaping are techniques used to control the rate of traffic. Policing drops or marks down packets that exceed a specified rate, while shaping buffers excess traffic and transmits it at a later time to smooth out bursts.

Example: Consider policing as a speed limit enforcement. Just as a speed limit ensures vehicles do not exceed a certain speed, policing ensures traffic does not exceed a certain rate. Shaping, on the other hand, is like a traffic light that regulates the flow of vehicles to avoid congestion.

5. Queuing

Queuing involves managing the order in which packets are transmitted. Different queuing algorithms (such as FIFO, PQ, WFQ) are used to prioritize traffic based on its importance.

Example: Think of queuing as a line at a grocery store. Just as customers in a priority lane get served first, packets in a priority queue get transmitted first, ensuring critical traffic is handled promptly.