8.1 Introduction to QoS Explained
Key Concepts of QoS
Quality of Service (QoS) is a set of techniques and mechanisms used to manage network traffic and ensure the reliable delivery of content. Key concepts include:
- Classification: Identifying and categorizing different types of traffic.
- Marking: Tagging packets to indicate their priority.
- Policing and Shaping: Controlling the rate at which traffic is sent or received.
- Queuing: Managing the order in which packets are processed.
- Congestion Management: Techniques to handle network congestion.
Classification
Classification involves identifying and categorizing different types of network traffic. This is typically done based on criteria such as source and destination IP addresses, port numbers, and protocol types. Classification helps in prioritizing critical traffic over less important traffic.
Example: In a corporate network, VoIP traffic can be classified as high-priority, while file transfers can be classified as low-priority. This ensures that voice calls are not interrupted by large file transfers.
Marking
Marking involves tagging packets with a priority level to indicate their importance. This is often done using Differentiated Services Code Point (DSCP) values or 802.1p tags. Marking helps network devices to prioritize packets based on their tags.
Example: When a VoIP packet is marked with a high DSCP value, routers and switches in the network will prioritize this packet over other packets with lower DSCP values, ensuring better voice quality.
Policing and Shaping
Policing and shaping are techniques used to control the rate at which traffic is sent or received. Policing drops or marks down packets that exceed a specified rate, while shaping queues packets to be sent at a controlled rate. These techniques help in managing bandwidth and preventing congestion.
Example: In a home network, traffic from a video streaming service can be shaped to ensure that it does not consume all the bandwidth, leaving enough for other applications like web browsing and gaming.
Queuing
Queuing involves managing the order in which packets are processed and transmitted. Different queuing algorithms, such as FIFO (First In, First Out), PQ (Priority Queuing), and WRR (Weighted Round Robin), can be used to prioritize certain types of traffic.
Example: In a network with critical and non-critical traffic, Priority Queuing can be used to ensure that critical traffic (e.g., VoIP) is always processed before non-critical traffic (e.g., email), improving overall network performance.
Congestion Management
Congestion management techniques are used to handle network congestion, which occurs when the demand for network resources exceeds the available capacity. Techniques such as Random Early Detection (RED) and Weighted RED (WRED) can be used to drop packets proactively and prevent congestion.
Example: In a busy data center, WRED can be configured to drop less important packets (e.g., background downloads) before the network becomes congested, ensuring that critical applications continue to function smoothly.