|
The use of native Internet Protocol (IP) technology is growing in every sector — and security is no exception. Everyday the market receives new products that capitalize on the rise of IP as the predominant network. Use of standard wiring and cheap off-the-shelf Ethernet switches and routers make Ethernet/IP the media of choice for many new applications. Just like in other market areas, Ethernet/IP is fast becoming the networking vehicle of choice for video surveillance cameras.
Ethernet/IP is the preferred network for many devices. Another technology that also is fast becoming key to their market viability is Power over Ethernet (PoE). Introduced in the 1990s, the first market success for PoE was in powering Infrared Data Association (IrDA) network interfaces, the precursors to today's wireless access points. Over the next several years only a few vendors used PoE for their niche devices because they were reluctant to incorporate proprietary power systems in their otherwise standards-based products. This changed when the IEEE standardized PoE in June of 2003, after which the market use of PoE exploded. Now as the IEEE works to increase the power available to network powered devices, the market is expected to have new momentum to increase this explosive growth. PoE and the pending IEEE enhancements make a wide variety of video surveillance cameras feasible.
Types of Cameras
IP security cameras come in many varieties and are, to some extent, subject to the manufacturer's definition of what an IP camera is. Some manufacturers utilize analog cameras which attach to a central IP decoder. Others convert the video signal inside the camera body and run IP natively from the camera itself. Even within the body for native IP, some cameras are manufactured for wired Ethernet while others contain wireless data. This article is directed at the needs of the wired Ethernet/IP camera and limited to the discussion of powering IP cameras utilizing PoE technology.
Wired Ethernet/IP has several advantages over competing technologies. The structured cabling that supports wired Ethernet is well-defined and ubiquitous in the market. Wired connections are intrinsically more secure than wireless data transfers that are broadcast in a wide radius. A perpetrator must gain physical access to the network to eavesdrop or spoof the information stream. Wired Ethernet can supply power also via PoE, so that powering remote devices is simplified. In most jurisdictions, installation of data cabling is not tightly regulated where installation of AC power requires licensed installers and many times a permitting process. Power over Ethernet also makes it simple to provide centralized power backup. If the wiring is installed in conduit, the end-to-end connection can be both reliable and very secure.
Today's current standard for PoE was ratified by the IEEE in June of 2003 as IEEE Std 802.3af-2003. Since then, this standard has been incorporated into the body of the main Ethernet standard as Clause 33 during the regular revision process that created IEEE Std 802.3-2005. There are no differences between the text of the original freestanding document and the roll-up. However, with the release of the 2005 edition, IEEE Std 802.3af-2003 has become obsolete, technically speaking.
The IEEE standard for PoE allows devices such as IP cameras to source no more than 12.95W at the RJ-45 connector. In practical terms, this means that the application circuitry can expect to see only about 10W due to the combined losses of rectification diodes, the front-end and DC/DC converter efficiency. The limitation to 10W or less means that camera designers must be constantly on guard against going over the power budget. While the power budget is tight, a reasonable limitation on the feature set and careful design of the application circuit allow for standards-compliant PoE to power IP cameras.
Figure 1 is a representative block diagram for a stationary surveillance camera which is appropriate for indoor fixed-location observations. Depending on the choice of processor and imager, adding an intermediate decoder may be required. Some applications may include audio surveillance. An optional block for audio input is shown. Notably missing from Figure 1 are power-hungry features such as support for Pan/Tilt/Zoom motors, or anti-fogging heaters for outdoor use.
Figure 1. Representative block diagram for a stationary surveillance camera
|
