8 Quality of Service (QoS) Explained
Key Concepts of Quality of Service (QoS)
Quality of Service (QoS) is a set of techniques used to manage network traffic and ensure the performance of critical applications. Key concepts include:
- Classification: Identifying and categorizing network traffic based on various criteria.
- Marking: Tagging packets with specific QoS markings to prioritize them.
- Policing and Shaping: Controlling the rate of traffic to prevent congestion.
- Queue Management: Managing the order and priority of packets in the queue.
- Congestion Management: Techniques to handle network congestion.
- DiffServ (Differentiated Services): A QoS model that classifies and manages traffic based on predefined service classes.
Classification
Classification involves identifying and categorizing network traffic based on various criteria such as source IP address, destination IP address, protocol, and port number. This helps in applying specific QoS policies to different types of traffic.
Example: In a network, VoIP traffic can be classified based on the destination port number (e.g., UDP port 5060). This classification allows the network to prioritize VoIP traffic over other types of traffic.
Marking
Marking involves tagging packets with specific QoS markings, such as DSCP (Differentiated Services Code Point) or 802.1p, to prioritize them. These markings help network devices to identify and treat packets according to their priority level.
Example: VoIP packets can be marked with a DSCP value of EF (Expedited Forwarding) to ensure they receive the highest priority in the network.
Policing and Shaping
Policing and shaping are techniques used to control the rate of traffic to prevent congestion. Policing drops or marks packets that exceed a specified rate, while shaping queues packets to transmit them at a controlled rate.
Example: In a network, you can configure policing to drop packets that exceed a certain bandwidth limit (e.g., 1 Mbps) for non-critical traffic, while shaping ensures that critical traffic (e.g., VoIP) is transmitted smoothly without exceeding its allocated bandwidth.
Queue Management
Queue management involves managing the order and priority of packets in the queue. Techniques such as FIFO (First In, First Out), PQ (Priority Queue), and WFQ (Weighted Fair Queueing) are used to ensure that high-priority traffic is processed first.
Example: In a network, you can configure a Priority Queue (PQ) to ensure that VoIP packets are always processed before other types of traffic, thereby maintaining the quality of VoIP calls.
Congestion Management
Congestion management techniques are used to handle network congestion. These techniques include RED (Random Early Detection), WRED (Weighted Random Early Detection), and CBQ (Class-Based Queueing) to prevent and manage congestion effectively.
Example: In a network, you can configure WRED to drop packets randomly before the queue becomes full, ensuring that high-priority traffic is less likely to be dropped during congestion.
DiffServ (Differentiated Services)
DiffServ is a QoS model that classifies and manages traffic based on predefined service classes. It uses DSCP values to mark packets and applies different treatment policies to each class of traffic.
Example: In a network, you can define different service classes such as EF (Expedited Forwarding) for VoIP, AF (Assured Forwarding) for web traffic, and BE (Best Effort) for general traffic. This allows the network to prioritize critical applications while managing other traffic efficiently.