Quality of Service
Since different applications — for example, telephone, e-mail and surveillance video — may be using the same IP network, there is a need to control how network resources are shared to fulfill the requirements of each service. One solution is to let network routers and switches operate differently on different kinds of services (voice, data, and video) as traffic passes through the network. By using Quality of Service (QoS), different network applications can co-exist on the same network without consuming each other’s bandwidth.
The term, Quality of Service, refers to a number of technologies such as Differentiated Service Codepoint (DSCP), which can identify the type of data in a data packet and so divide the packets into traffic classes that can be prioritized for forwarding. The main benefits of a QoS-aware network include the ability to prioritize traffic to allow critical flows to be served before flows with lesser priority, and greater reliability in a network by controlling the amount of bandwidth an application may use and thus controlling bandwidth competition between applications. PTZ traffic, which is often regarded as critical and requires low latency, is a typical case where QoS can be used to guarantee fast responses to movement requests. The prerequisite for the use of QoS within a video network is that all switches, routers and network video products must support QoS.
Ordinary (non-QoS aware) network
In this example, PC1 is watching two video streams from cameras 1 and 2, with each camera streaming at 2.5 Mbit/s. Suddenly, PC2 starts a file transfer from PC3. In this scenario, the file transfer will try to use the full 10 Mbit/s capacity between the routers 1 and 2, while the video streams will try to maintain their total of 5 Mbit/s. The amount of bandwidth given to the surveillance system can no longer be guaranteed and the video frame rate will probably be reduced. At worst, the FTP traffic will consume all the available bandwidth.
QoS aware network
Here, Router 1 has been configured to devote up to 5 Mbit/s of the available 10 Mbit/s for streaming video. FTP traffic is allowed to use 2 Mbit/s, and HTTP and all other traffic can use a maximum of 3 Mbit/s. Using this division, video streams will always have the necessary bandwidth available. File transfers are considered less important and get less bandwidth, but there will still be bandwidth available for web browsing and other traffic. Note that these maximums only apply when there is congestion on the network. If there is unused bandwidth available, this can be used by any type of traffic.