Down to the Wire

Signal transmission methodology is an essential ingredient to optimize a video surveillance system. While more than half of existing systems use coaxial, Ethernet cabling is growing fast as IP-based systems proliferate. And then there’s fiber optics. Learn how to evaluate and balance critical factors to achieve the best results.

With a transition from analog to digital video surveillance continuing, there remains a crucial requirement for reliable transmission of the video signal during today’s period of coexistence. There are several hardwired and wireless technologies available to carry this visual information through a surveillance system, but understanding the strengths and limitations of each one and properly matching it to the application is essential.

With many legacy installations, it has been coaxial cable handling images from a camera to monitoring or recording, or both. Indeed, for years coax has been the traditional transmission method of video surveillance traffic. The presence of a coax BNC connector on most every security camera underlines this established signal transmission practice. However, coax has its limits, including restricted transmission distance, signal degradation over long cable runs and interference, to name a few.

Networking, digital and IP have ushered in high-speed Ethernet and Category-5/unshielded twisted-pair (UTP) cable, employing IP to carry the digitalized video images. Lastly, of the wired technologies, there is fiber-optic cabling with its interference immunity, better inherent security, robust cabling distances and huge bandwidth capability.

Needless to say, there are differences among transmission methods. Security integrators, system designers, installers and end users must consider and balance the methods with the needed functionality of cameras in light of: maximum cable run distances; power requirements; installation issues; installation time; quality of video; integration with other systems; and cost.

Coax Can’t Go the Distance

The most common coax cable is RG-59U. It provides what many believe is an acceptable quality video path from a camera to the head end out to 750 feet. That’s because the maximum recommended distance between an analog security camera and a DVR, head-end or monitor is 750 feet. When it comes to power to the camera, many installations employ so-called Siamese cable — a single RG-59U wedded to an attached 18/2 cable for both power and video. Still some distances will increase voltage drop, making it necessary to select a power supply and cabling that match necessary voltage to distances.

Coax’s tie to analog cameras explains why it is still the most popular technology and why it is losing market share the fastest. As more IP surveillance systems come onboard, there is less desire to use coax. Today, and especially when it comes to new and upgraded installations containing many cameras, fewer of these new systems use coax while an increasing number boast Ethernet/IP (EIP) networks, Cat-5/UTP and fiber.

In some ways, the security shift has been spurred by the popularity of local area networks (LANs) in most enterprises. The IT world’s means of transmission gravitated toward Cat-5/UTP wiring as well as fiber, often as an overall communications backbone. Cameras can be more easily installed using existing UTP cabling or fiber previously laid for enterprise network use. Corporate and government IP-based platforms have accelerated the transition. That naturally has swung security to such designs, especially when it involves video surveillance.

Ethernet/IP Transmission Is Growing

IP security cameras and video servers (also called IP encoders) are connected to a network using either an Ethernet connection or Cat-5/UTP cabling. In many facilities, the Ethernet cabling and protocol is already present so the cameras and servers can be easily dropped in. IP cameras and video servers have built-in Web servers so that the surveillance video they transmit can be viewed directly from the camera over the Internet using a standard Web browser. There is no need for a DVR or video capture card in order to broadcast the surveillance video over the Internet. IP video servers, also known as network video servers, can turn any CCTV camera (with a standard BNC output) into an IP-based network camera (Ethernet output).This diagram shows the topology of how a networked video surveillance system might be configured in the application of a metro transit system.

A metro transit system serves as a good example of how to leverage EIP, yielding easy connection, simple system expansion, strong compatibility and reliability (see diagram). The control center and each station in the metro transit system are connected by an Ethernet network, used solely for the video surveillance system, to offset problems of electromagnetism. A matrix in any one of the metro stations uploads eight channels of images through eight video encoders. Eight video decoders in the control center then take the images collected from the front matrix and transmit them to the central control matrix. All matrixes are also connected via Ethernet, each provided with its own IP address.

The central control keyboard is also connected to the Ethernet network instead of the central control matrix. Its control signal is transmitted from a keyboard to the video management server. Once the server translates codes collected from the keyboard, it identifies their priority and transmits the corresponding demand that controls each station, central matrix and codec to perform image switching and pan/tilt/zoom (p/t/z) operation for the domes in each station.

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