QoS Traffic Shaping Basics

Introduction to Quality of Service

Quality of Service (QoS) is a set of technologies that work on a network to guarantee its ability to dependably run high-priority applications and traffic under limited network capacity. QoS is primarily used to manage latency, jitter, and packet loss.

Traffic Shaping

Traffic shaping is a QoS technique used to control the rate of traffic sent into a network. It regulates the flow of packets to ensure they do not exceed a configured rate (the shaping rate).

How Shaping Works

When the traffic rate exceeds the configured shaping rate, the excess packets are retained in a queue (a buffer) rather than being dropped immediately. They are transmitted later when the traffic rate falls below the shaping rate.

Queuing

Queuing is a fundamental component of traffic shaping and QoS in general. When a network interface is congested, packets must wait in a queue until the interface is available.

Common Queuing Mechanisms

• FIFO (First-In, First-Out): The simplest form of queuing. Packets are sent in the exact order they arrive.
• CBWFQ (Class-Based Weighted Fair Queuing): Allows you to define traffic classes and assign a guaranteed minimum bandwidth to each class during times of congestion.
• LLQ (Low Latency Queuing): Adds a strict priority queue to CBWFQ, primarily used for delay-sensitive traffic like voice and video.