|Often our selection of a network switch
is based on price or major brand names,
both of which can lead to problems
Networking Basics for Security Professionals: How bandwidth requirements guide selection of network switches
If a network switch looks like a network switch, is it a network switch that will work for IP video security applications? The surprise answer is “not necessarily.”
There are major differences between the network switch performance required for data applications such as word processing, accounting and web browsing and that required for IP video for security applications. These differences have a major effect on performance. Often our selection of a network switch is based on price or major brand names, both of which can lead to problems.
The bandwidth output of IP security cameras is 100Mbps; in networking, output speed must be matched by input switch port speed. However, in most cases switch ports operating at 100Mbps limit their packet size or video frame in our case to about 1518 bytes. This is equal to about a 2-3 megapixel camera. The higher the pixel count, the larger the video frame and higher the number of bytes contained in that frame. Packet sizes greater than 1518 bytes are generally referred to a Jumbo Frames. The inability of a port switch to handle Jumbo Frames can result in blocking information from higher-end megapixel cameras starting at about 3 megapixels. To handle larger megapixel cameras, a network switch must be able to be programed for up to 9600 bytes when the port bandwidth is 100Mbps.
Network switches that provide for 1 Gigabyte port bandwidth settings provide the ability to resolve Jumbo Frames; however, the mismatch between the 100Mbps output of the camera and input of the switch is often overlooked. It’s a mistake to interpret that the switch will have this same ability at 100Mbps. Faulty settings applied to high-megapixel cameras can result in distorted video or inability to pass video at all.
When addressing the actual
number of usable ports, port
packet handling and switch
fabric bring up the point that
there are no standards for these
The second consideration is called either throughput or switch fabric. This defines the bandwidth that connects all the switch ports. In many data-only applications, the maximum port bandwidth is never achieved. In order to ensure that high-bandwidth video is passed, the switch fabric must at least two times the total bandwidth of all the ports. For example, a 24 port Gigabyte switch needs to have a switch fabric of 48 Gigabytes. Switches with less can exhibit video quality issues if all ports are used, which is usually the case with IP video applications.
The third area that is often overlooked is the actual number of ports. A switch advertised as a 24-port does have 24 actual ports. However, that doesn’t mean you can use all 24 ports. First there is the consideration of how the switch is positioned within the network. Often this requires an up and downlink. As such, two ports are lost and reduces the usable ports to 22. Some manufacturers realize this and limit the application of power over Ethernet (PoE) to only 20 ports or the total number of ports minus 2. This also makes their PoE specification look better, but denies you of the use of two ports.
When addressing the actual number of usable ports, port packet handling and switch fabric bring up the point that there are no standards for these features. In a competitive network switch market, manufacturers design products to meet the most competitive pricing for the majority of applications. Our market’s major concerns are large packets, video frames and high internal bandwidth. These remain minority concerns with the majority of network switches that don’t cater to video security IP applications.