Most of you define a home network as a system that links two or more PCs in the home. Yet that's only part of the picture. Home control networks have existed for years, but interest has recently been rekindled. Furthermore, there's a growing interest in and need for home entertainment networks.
However you define it, home networking is definitely not just a fad. Current estimates say that about 3% to 5% of U.S. homes already have some kind of home network. These are the high-tech early adopters, but the real consumers are expected to join the home networking movement as products become available and prices decrease. Several major magazines now cover this field at the consumer level. Check out Home Automation, Electronic House, and Penton's Connected Home magazines at your local newsstand.
The Wired Home LAN: The most common reason for a home network is sharing some major resource like a printer or high-speed Internet connection. A server-like device called a residential gateway accomplishes this by connecting to your high-speed cable TV line or DSL line. The gateway then distributes the signals to the various PCs on the network via the chosen communications medium—cable, wireless, or power line.
The most direct approach is to just wire up a simple 10- or 100-Mbit/s Ethernet LAN using category 5 (CAT5) twisted-pair cable. Cheap Ethernet network interface cards (NICs) for PCs are readily available. Most new PCs and laptops have a 10/100-MHz Ethernet port built in. Buy an inexpensive four-port Ethernet hub to connect the gateway to the PCs. Running the cable is the hard part. Even the serious do-it-yourselfers won't find it easy. Or maybe you're lucky enough to own one of the many new homes prewired with CAT5.
Another option is to use the house electrical wiring to carry the data from computer to computer. Because every room has multiple outlets, network connections are available everywhere. The data signals are superimposed on the 120-V, 60-Hz sine wave. The data is carried to all outlets simultaneously.
Also known as carrier current communications, power-line networking has functioned in the electrical power industry for years. But power lines are extremely lossy and noisy. Both conditions severely limit data rate and distance.
Over the years, several different power-line networking technologies have developed, including X10, CEBus, and LonWorks. Most are used for telemetry and control operations rather than for carrying high-speed data.
But the latest technology really overcomes the problems of power-line networking. Named HomePlug 1.0, it's supported by over 80 companies. Gateways and interfaces are just now becoming available. This standard tolerates up to a 14-Mbit/s data rate using orthogonal frequency division multiplexing (OFDM) implemented in DSP.
A typical power-line network system is the new NeverWire 14 QX-201 from Phonex Broadband (Fig. 1). According to Brad Warnock, director of marketing for Phonex, the unit runs at 14 Mbits/s, but protocol overhead drops the actual transfer rate to about 8 Mbits/s. Up to 16 units may be connected on the network. As for distance, Phonex says you can wire up to about 1000 ft of ac power wiring.
Therefore, you can easily network the average house. You can even network between nearby buildings, apartments, or offices. When networking in an apartment, security becomes important. The Phonex units have a built-in Digital Encryption Standard capability using a 56-bit encryption key.
The heart of the Phonex units is the Intellon INT51X1 chip, which implements the HomePlug 1.0 standard. You will undoubtedly see this chip in other power-line interfaces, or use it yourself. Both Ethernet and USB interface options are available.
Another company making HomePlug 1.0 chips is Cogency Semiconductor Inc. Its new Piranha chip set consists of the CS1102 Ethernet MAC/PHY implemented in firmware that can be customized to the application, and the companion AD9875 mixed-signal front end made by Analog Devices. A version for USB is available too, as are reference designs.
Cogency also makes power-line networking end products, specifically wall adapter units that plug directly into an ac outlet. Both Ethernet and USB versions are available. Figure 2 shows the basic block diagram of the USB interface.
Another wired option is the existing home telephone wiring. While most homes don't have as many telephone jacks as power outlets, the available telephone wiring is typically sufficient to eliminate the need for installing other wiring. Several companies supporting the Home Phoneline Networking Alliance standard make NIC cards that plug into any nearby RJ-11 modular jack. The data is then available at all other phone jacks. The current standard moves 10 Mbits/s, but future versions will feature up to 100 Mbits/s.
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