The word originated as a reference to radio transmission signals. Frequency band - or just band, for short - means a specific range of frequencies in the radio frequency spectrum. This spectrum is divided into ranges from very low frequencies to extremely high frequencies. Each band has a defined upper and lower frequency limit, which establishes its bandwidth. The wider the bandwidth, the more signals can be transmitted within the band, much the same as a wider highway can allow more cars to travel at the same time.
Frequency is measured in the number of cycles of change per second, or hertz. In analog systems, bandwidth is calculated as the difference between the highest-frequency signal component and the lowest-frequency signal component. The full range of the human voice is 300 Hz to about 5 kilohertz (kHz), which is a 4.7 kHz analog bandwidth. Most speech occupies a smaller portion of that range, giving typical voice signals a bandwidth of about 3 kHz.
In digital systems, bandwidth has come to mean the measure of the maximum data speed. Bits per second (bps) is a common measure of data speed for computer modems and computer data transmission carriers, and means the number of data bits transmitted or received each second.
A network is often composed of multiple segments, each segment being one point-to-point wiring or radio connection between pieces of network equipment, or between network equipment and computers. Different segments can have different bandwidths, depending upon how much network traffic they are designed to carry.
For security networks that involve WAN connections, bandwidth requirements may have significant cost or network resource impacts. For example, Telco-based connections have a recurring monthly cost. If the security network requires expanding the capacity of a Telco connection, that will mean an increase in the monthly cost.
Usually, one-time costs come from a capital budget while recurring costs come from an operations budget. These two budget categories are entirely separate, with entirely separate budgeting processes and revenue streams.
CCTV is the main reason security network bandwidth is an issue. An analog television broadcast video signal has a bandwidth of 6 megahertz (MHz) - 2,000 times as wide as a voice signal. This provides an indication of why sending CCTV video streams over a network can use up all available network bandwidth, and why the capacity of standard telephone lines is insufficient for transmitting continuous video. The bandwidth requirements of video are much higher than either voice or computer data.
In addition, digital video management software makes it possible to view live and recorded video by computer over an Ethernet network, using a technique called video streaming. The larger the CCTV system, the greater the potential for multiple users to be viewing multiple cameras.
Each camera requires its own data stream. Even with video data compression techniques, security-quality video can take up to 1 Mbps of bandwidth per camera, for each person viewing the camera signal. Multicast technology (routing a single video stream over the network to multiple users) can reduce the number of streams to a single stream per camera, regardless of the number of users viewing the video stream.
However, currently only two or three security video management software applications have multicast capability.
Video technologies will continue to improve, requiring less and less bandwidth per camera. On the other hand, the demand for higher-quality video (with higher bandwidth requirements) will also continue to increase for both security and operations use.
It wouldn't be wise to look to technological improvements to reduce security's overall requirement for network bandwidth. As security functions increase and improve, and as camera technologies both improve and lower in price, stronger security and business cases can be made for increased utilization of CCTV.This means that estimating security bandwidth requirements will remain an important element of security system design and planning, especially for large-scale security networks that involve WAN connections.
Estimating Security Network Bandwidth
Security networks have to be designed to handle the "worst case" scenario in terms of bandwidth. This would be a situation in which multiple security and operations personnel would have to make maximum use of networked equipment, such as examining live and recorded video from multiple cameras. This could easily require 10 or 20 times the network capacity that is normally needed for security.