Quality of Service (QoS)
Fundamentally different networks are merging into one IP network. For example, telephone and video (CCTV) networks are migrating towards IP. In these networks, there is a need to control shared network resources to fulfil the requirements of each service. One solution is to let the network routers and switches behave differently on different kinds of services (voice, data, video) as the traffic passes through the network. This technique is called Differentiated Services (DiffServ). By using QoS, different network applications can co-exist on the same network, without consuming each other’s bandwidth.
Definition
The term Quality of Service refers to a number of technologies to guarantee a certain quality to different services on the network. Quality can be, for instance, a maintained level of bandwidth, low latency, no packet losses, etc. The main benefits of a QoS-aware network can be summarized as:
The ability to prioritise traffic and thus allow critical flows to be served before flows with lesser priority.
Greater reliability in the network, thanks to the control of the amount of bandwidth an application may use, and thus control over bandwidth races between applications.
To use QoS in a network with network video products, the following requirements must be met:
All network switches and routers must include support for QoS. This is important to achieve end-to-end QoS functionality.
The network video products used must be QoS-enabled.
QoS Examples
[non-QoS aware network]
In this example, PC1 is watching two video streams from cameras Cam1 and Cam2, with each camera streaming at 2.5 Mbps. Suddenly, PC2 starts a file transfer from PC3. In this scenario, the file transfer will try to use the full 10 Mbps capacity between the routers R1 and R 2, whilst the video streams will try to maintain their total of 5 Mbps. 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]
The router R1 has been configured to devote up to 5 Mbps of the available 10 Mbps for streaming video. FTP traffic is allowed to use 2 Mbps, and HTTP and all other traffic can use a maximum of 3 Mbps. 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.
About Pan/Tilt/Zoom (PTZ) traffic
PTZ traffic is often regarded as critical and requires low latency to guarantee fast responses to movement requests. This is a typical case in which QoS can be used to provide the necessary guarantees. The QoS control of PTZ traffic in Axis network video products is handled by the ActiveX viewer AXIS Media Control (AMC), which is automatically installed the first time the Axis product is accessed from Microsoft Internet Explorer.
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