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The transition in video surveillance from traditional analog to more advanced digital technologies is still in its infancy, but the advantages are clear. Digital video surveillance systems operating over Internet protocol (IP) networks offer lower installation costs and scalability. But the technology may also introduce new, often unplanned requirements and stresses on network bandwidth and storage resources.
Several trends in the video surveillance market have resulted in higher loads on networks and greater demands on video storage as opposed to analog systems that usually have dedicated cabling and embedded hard drives. Vertical markets users, for example big-box retailers, have as many as 100 cameras, multiplied by thousands of locations, while large-scale municipal and casino projects are growing with thousands of cameras per site. Camera installations of this size far exceed the bandwidth capabilities of an average 100Base-T corporate local area network (LAN), so dedicated video networks are required to support the bandwidth.
Saving critical images
Video archiving requirements are constantly growing. It is quite rare for a video surveillance project of any size to make due with the 24-hour loop of video that was commonplace with analog video cassette recorders (VCR). Most projects now require a minimum of seven days of storage for every camera and often as much as 30 to 60. For purposes of positive identification in investigations and trials, quality images and smooth motion is a must.
Digital megapixel cameras available for under $1,000 are now capable of high-definition image capture at frame rates approaching broadcast quality. For example, a five megapixel camera on the market is capable of producing 15 frames per second at a 2560 x 1600 resolution, transmitting motion JPEG data at up to 55 megabits per second (Mbps). While the decreasing price point for cameras of this resolution are making them attractive to surveillance system designers, a single camera of this size would quickly consume a large percentage of available network bandwidth. A megapixel camera recording can also take up to 24.8 gigabytes of disk space every hour.
With the image quality and price for digital IP cameras reaching parity with analog cameras, surveillance system designers and operators may be forced to compromise image quality in order to keep bandwidth and storage requirements within reasonable limits. Whether IP cameras or analog with encoders, you can expect each camera on a network to require an absolute minimum of 250 kilobits per second (Kbps) of bandwidth for acceptable image quality. For most applications, cameras on a digital surveillance network will consume an average of 1Mbps for reasonable video quality at 4CIF resolution and 15 frames per second (fps). The bandwidth and frame rate in a camera can be configured to float freely below a threshold to consume fewer resources when no motion exists in the field of view. Then the bandwidth spikes with complex motion or activity in the frame so a higher quality recording results.
Storage innovation
Most IP video surveillance applications rely on network attached storage (NAS) because they are highly scalable systems that offer superior performance and reliability over direct-attached storage (DAS). More recently, some video surveillance solutions have begun using storage area network (SAN) technologies to leverage existing corporate data.
After selecting the appropriate video compression, implementing the right networked storage solution and fine-tuning image quality to preserve bandwidth, the final stage for surveillance system designers and operators is to configure the network video recorders to intelligently optimize how the video is recorded. The application will determine how you deploy video over the network and ultimately its effectiveness.
Jason Schmitt is the product manager for Steelbox Networks.
author: By Jason Schmitt