Quality of Service

Quality of Service (QoS) is the capability to adjust some quality aspects of your overall network traffic. This can include such techniques as priority-based queuing and traffic policing. Because bandwidth is finite and because some types of traffic are slow, jitter or packet loss sensitive, bandwidth intensive, or operation critical, QoS can be a useful tool for optimizing the performance of the various applications on your network.

Before implementing QoS, organizations should first identify the types of traffic that are important to the organization, the types of traffic that use high amounts of bandwidth, and the types of traffic that are sensitive to latency or packet loss.

For example, a company might want to guarantee sufficient bandwidth for revenue producing e-commerce traffic. They need to ensure that transactions can be completed and that clients do not experience service delays and interruptions. At the same time, the company may need to ensure low latency for voice over IP (VoIP) traffic used by sales and customer support, while traffic latency and bursts may be less critical to the success of other network applications such as long term, resumable file transfers. Many organizations discover that QoS is especially important for managing their voice and streaming multi-media traffic. These types of traffic can rapidly consume bandwidth and are sensitive to latency.

Discovering the needs and relative importance of each traffic type on your network will help you to design an appropriate overall approach, including how you will configure each available QoS component technique. Some organizations discover that they only need to configure bandwidth limits for some services. Other organizations determine that they need to fully configure interface and security policy bandwidth limits for all services, and prioritize queuing of critical services relative to traffic rate.

You can implement QoS on FortiGate units using the following techniques:

Traffic policing                         Drops packets that do not conform to bandwidth limitations.

Traffic shaping

Ensures that the traffic may consume bandwidth at least at the guaranteed rate by assigning a greater priority queue if the guarantee is not being met. Also ensures that the traffic cannot consume bandwidth greater than the maximum at any given instance in time. Flows greater than the maximum rate are subject to traffic policing.

Queuing      Transmits packets in order of their assigned priority queue for that physical interface. All traffic in a higher priority traffic queue must be completely transmitted before traffic in lower priority queues will be transmitted.

When deciding how to configure QoS techniques, it can be helpful to know when FortiGate units employ each technique in the overall traffic processing flow, and the considerations that arise from those mechanisms.