Blog Date: 5/19/2011
Author: Ray Coulombe

As Ethernet networks have moved to becoming the norm for IP-based transmission of video, audio and data signals, I wanted to examine some alternatives for transmission. By now, most of us are familiar with common Ethernet media — Cat 5e, Cat 6, fiber optic cable, and WiFi. Today, Cat 5e and Cat 6 are the baseline means for Ethernet transmission, at least for horizontal cabling to the wiring closet. This cable is relatively inexpensive and well-understood. But what if running new copper or fiber media is problematic, due to facility or budget constraints, and the conditions for wireless are not right for reliable deployment? Alternatives exist.
The first is to use existing unused or abandoned copper media. There are now several manufacturers of products to transmit IP signals over coax cable, including Aboundi, Veracity and Vigilant. These products are reasonable choices where excess coax may be available due to conversion from analog to IP cameras. There are also devices that allow using twisted pair (apart from Cat 5e and Cat 6) cables. DSL (digital subscriber line) is one family of technologies that may be employed for this, although the cost of DSL modems may be a barrier. Asymmetric DSL (ADSL) uses two frequency bands, 26.000kHzto 137.825kHz for upstream communication and 138kHz — 1.104MHz for downstream, where each band is divided into frequency “bins” of 4.3125kHz. The system then uses those bins where distortion is least and transmission can be optimized. In telephony, these frequencies reside above the frequency space used for voice channels, allowing voice and Internet traffic to happen over the same twisted pair. This introduces the next alternative, existing active copper media. Security functions are performed over many types of wire — coax, twisted pair for audio and data, even power. Any of these has the potential to share its signal capacity, if signals to be added can find their way onto the media. Consider this: In the old world of security, most transmission is baseband, where the largest bandwidth user is video, typically up to 5 MHz. RF technology exists today — such as that used in the IEEE G.hn standard for home networking technology that uses wireless OFDM techniques over wire — creating information-carrying capability in frequency spaces above where the conductor is already being used. In a way, this resembles DSL where network signals reside in the frequency space above voice communication. While home networking technology is based on piggybacking onto AC wiring, there is potential to use this technique with most other types of wiring. Theoretically, any conductor with a baseband signal can tolerate higher piggybacked frequencies as long as the impedance of the cable is appropriate, distortion issues can be managed, and there is sufficient frequency separation. Imagine as cables for power supplies, access control systems, intercom, telephone, and more become candidates for Ethernet transmission. Existing installations which have not undergone cabling or network upgrades can be provisioned with network capability. The infrastructure for analog devices can support some networking functionality until the time is right for upgrade to IP.
Link to Complete Article as it appeared in Security Technology Executive Magazine

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