Demystifying Wired Communications for IP-Based Security Applications

Standard networking cable is an ideal medium for wired data communications as it has been specially developed for the purpose of transmitting Ethernet network signals at high speed (up to 1 gigabit per second). It has the added advantage that so many systems are designed for CAT5e cabling with the ubiquitous RJ45 connectors. Almost everyone is familiar with this standard “network cable.”

However, for security applications and for video surveillance in particular, it does have a serious limitation: distance. After approximately 100 meters, the Ethernet signal is liable to dropouts and failed connections [search “Ethernet distance limit”]. This is never much of a problem in a structured, cabled office, where multiple switches and routers are on every floor and each network device is rarely more than dozens of meters away from such a connection. However, network cameras often need to be deployed at the peripheries of a site (fence lines, parking lots, entrances and exits, walkways, access roads and so on). These are usually more than 100 meters from the nearest switch. This also holds true, although slightly less so, for access control devices, VoIP phones and help points.

There is an easy solution to this distance problem, thanks to LAN and PoE extenders which have become available in the last couple of years. These are small network repeaters powered through the network connecting cable by PoE and are placed at or before the 100-meter Ethernet limit. They reconstruct and resend the Ethernet network packets (just like a switch) and so double the effective network cable transmission to 200 meters. Multiple devices can be deployed to reach 300 meters, 400 meters and so on. Depending on the power injected and the distance required (and indeed the power consumption of the repeater device), useful levels of PoE power can still be delivered at some distance [search “LAN and PoE extender”]. Such devices are becoming an essential part of an IP video system designer's toolbox.

These days, almost all Ethernet equipment runs at 100 megabits per second (Mbps) at least. Gigabit Ethernet is common, but requires high-quality cabling and is typically not supported by LAN and PoE extenders. However, this is rarely a problem, even for IP video using megapixel camera systems, as the long cable run sections usually carry only one, two, maybe four video streams at any point. In toward the center of the network (such as a main building) where the streams are aggregated at network switches, the switches and the rest of the network can run at Gigabit speeds, and the cable runs tend to be shorter from that point onward.

Thus, Ethernet over CAT5e/6 cabling is an almost universal solution and, with modern LAN and PoE extenders, is ideal for all types of security applications. Although this article is about wired communications, it is important to note that wireless network segments can seamlessly integrate with standard networks and greatly increase system design flexibility. However, the optimum siting of wireless access points for greatest signal coverage is often inconveniently more than 100 meters away from the nearest wired network point (switch). Again, LAN and PoE extenders can be exploited.

Product Adopted:
Fiber-Optic Transmission
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