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.
Fiber optics proved its worth in the security industry some years ago as an alternative to coax in analog video transmission and to other copper media for low-speed data and audio. Now, standards-based fiber optics is mainstream, and, in the future, the customized proprietary analog fiber links will likely give way to 100 Base F or Gig E transmission of IP video signals. I am actually surprised that analog links continue to be sold in quantity.
Wireless transmission also has its place, provided proper security measures are employed and the installation and transmission environments are suitable for deployment. We are seeing more products introduced with inherent or optional wireless capability, and wireless networks, such as mesh networks, are becoming more capable and robust.
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, 26.000 kHz to 137.825 kHz for upstream communication and 138 kHz — 1.104 MHz for downstream, where each band is divided into frequency “bins” of 4.3125 kHz. 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.
Because we are dealing with radio frequencies, there are opportunities for inductively coupling an additional Ethernet signal without the need to disconnect from existing signal equipment or power sources. This idea has great commercial promise, as the same approaches which are used in wireless and DSL transmission can be adapted to enhance throughput, including using frequency bands where throughput is best and errors are minimized. (see www.ds2.es/subsecciones-web/subsecciones-web.aspx?ID=3). Current technology promises throughput speeds up to 200 Mbps.