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Phone-line Networking
Phone-line networking is easy to install, inexpensive and fast, and it doesn't require any additional wiring.
Phone-line networking, most commonly referred to as HomePNA, is based on the specifications developed by the Home Phone Networking Alliance (HPNA). The HPNA is a consortium of key networking technology companies that created a phone-line standard for the networking industry. HPNA 1.0, the original version of the standard, operated at a rather slow 1 megabit per second (Mbps). The current specification, HPNA 2.0, is based on technology developed by Broadcom and operates at a faster 10 Mbps. Cards using HPNA 1.0 are still being sold, so make sure that the cards you buy are HPNA 2.0!
Pros and Cons of Phone Line Networking
HomePNA has several distinct advantages:
- It's easy to install.
- It's inexpensive.
- It's standardized.
- It's reliable.
- It operates at a constant 10 Mbps, even when the phone is in use.
- It requires no additional networking equipment (such as hubs or routers).
- It supports up to 25 devices.
- It is fast enough for bandwidth-intensive applications, such as video.
- It is compatible with other networking technologies.
- It works on Macs and older PCs (in addition to Windows systems).
HomePNA does have some drawbacks, though. You need a phone jack close to each computer. Otherwise, you will have to run phone extension cords or install new wiring. Even though it operates at a very reasonable 10 Mbps, it is still 10 times slower than fast Ethernet (100 Mbps). Therefore, if you are going to be sending huge amounts of data between your computers, you may want more speed. There is a physical limit of 1,000 feet (304.8 m) of wiring between devices, and the overall area of coverage should not exceed 10,000 square feet (929 m 2 ). Rarely (in fewer than 1 percent of U.S. homes), HomePNA will not work on the existing wiring. And while this author did not notice any interference with voice use, there have been reports of voices sounding "funny" or of a lot of noise on the phone once HomePNA is installed. Later, we will look at these issues and possible solutions.
How HomePNA Works
HomePNA uses a method known as frequency-division multiplexing (FDM) . FDM puts computer data on separate frequencies from the voice signals being carried by the phone line. FDM separates the extra signal space on a typical phone line into distinct data channels by splitting it into uniform chunks of bandwidth. To better understand FDM, think of radio stations -- each station sends its signal at a different frequency within the available band.
In HomePNA, voice and data travel on the same wires without interfering with each other. In fact, a standard phone line has enough room to support voice, a high-speed DSL modem and a home phone-line network.
How Much Does It Cost?
HomePNA adapters come in two versions: internal card (PCI) or USB. You can buy kits consisting of HomePNA cards for two computers, an installation CD and all the necessary cables for about $90 to $110. The actual cost of implementing HomePNA depends primarily on the type of interface you buy for each computer: PCI cards cost about $45 to $55, while USB adapters range from $75 to $85. If you plan to use a laptop computer that does not have a USB port, you can either buy a USB-to-PCMCIA adapter ($50) or get a parallel port USB adapter.
Since many phone lines in existing homes vary greatly in length and signal quality, the larger 4210 controller chip on the right has to be able to adapt to a variety of challenges. Because the 4210 does this so well, the HPNA estimates that more than 99 percent of U.S. homes have phone wiring that can support HomePNA. Basically, it works this way: First, the controller chip takes the unfiltered content it receives from the smaller chip and strips away all the noise. It then takes what is left and passes it on to the computer for processing. Once the computer processes the information, it returns an acknowledgment to the sending computer so it knows that the data was received. This happens thousands of times each second as the computers communicate.
How to Install HomePNA
If you decide that HomePNA is best for you, here are the basic steps:
- Buy a kit, making sure you have a HomePNA card or external adapter for each computer in your home.
- Install the hardware (internal card or external adapter).
- Plug the included cable into the hardware and into the phone jack.
- Install the software.
Troubleshooting
There are a few things you should keep in mind when you set up a HomePNA network. First, most analog communication devices, such as telephones and fax machines, create signal noise. Think of signal noise as debris on a major highway. A little debris probably won't affect traffic, but a lot of it could slow down or even stop traffic in one or more lanes. If you install a HomePNA network and your computers have trouble communicating, try inserting a low-pass filter between any phones or fax machines and their respective jacks. The low-pass filter will block noise without impeding the performance of your fax or phone. You can find these filters at most electronics stores.
Also, electrical fields generated by powered communication devices, such as cordless phones or fax machines, can introduce another type of signal noise. A different type of low-pass filter, inserted between the electrical wall outlet and the power cord for the device, can fix this problem.
The last potential issue is rare but much harder to fix. If you have a very large home, or one that has been renovated several times, you may have too much wiring between computers. All of this wiring will weaken the signal, causing it to fade out and lose strength. The result is that not enough of the signal remains if and when it reaches the other computer for that machine to process it. If this is the case, then you will either have to move the computers closer together or redo the wiring, at which point you may want to consider learning about wireless networking.
Wireless Networking
Wireless-networking technologies take the concept of "no new wires" one step further. In a wireless network, all of the computers in your home broadcast their information to one another using radio signals. This can make networking extremely easy, especially if you have computers all over your house. It also makes it a whole lot simpler to move computers around. For example, a laptop with a wireless-network card is completely portable throughout the house!
here are four types of wireless networks, ranging from slow and inexpensive to fast and expensive:
- Bluetooth
- IrDA
- HomeRF (SWAP)
- WECA (Wi-Fi)
(Infrared Direct Access) is a standard for devices to communicate using infrared light pulses. This is how remote controls operate, and the fact that all remotes use this standard allows a remote from one manufacturer to control a device from another manufacturer. Since IrDA devices use infrared light, they depend on being in direct line of sight with each other. Although you can purchase and install an IrDA-based network capable of transmitting data at speeds up to 4 megabits per second (Mbps), the requirement for line of sight means that you would need an access point in each room, limiting the usefulness of an IrDA network in a typical home layout.
| (RF stands for radio frequency) is an alliance of businesses that have developed a standard called Shared Wireless Access Protocol (SWAP) . A sort of hybrid standard, SWAP includes six voice channels based on the Digital Enhanced Cordless Telecommunications (DECT) standard and the 802.11 wireless-Ethernet specification for data. SWAP devices make 50 hops per second and transmit at 1 Mbps. Depending on the manufacturer, some of these can step up to 2 Mbps if there is very little interference in their operational area.
Here are the advantages of SWAP:
- It's inexpensive ($70 to $200 per device).
- It's easy to install.
- It requires no additional wires.
- It has no access point.
- It uses six full-duplex voice channels and one data channel.
- It allows up to 127 devices per network.
- It allows multiple networks in the same location.
- You can use encryption to make your data secure.
Here are the disadvantages of SWAP:
- It's not very fast (normally 1 Mbps).
- It has a limited range (75 to 125 ft / 23 to 38 m).
- It's not compatible with FHSS devices.
- Physical obstructions (walls, large metal objects) can interfere with communication.
- It's difficult to integrate into existing wired networks.
HomeRF and SWAP
HomeRF(RF stands for radio frequency) is an alliance of businesses that have developed a standard called Shared Wireless Access Protocol (SWAP) . A sort of hybrid standard, SWAP includes six voice channels based on the Digital Enhanced Cordless Telecommunications (DECT) standard and the 802.11 wireless-Ethernet specification for data. SWAP devices make 50 hops per second and transmit at 1 Mbps. Depending on the manufacturer, some of these can step up to 2 Mbps if there is very little interference in their operational area.
Here are the advantages of SWAP:
- It's inexpensive ($70 to $200 per device).
- It's easy to install.
- It requires no additional wires.
- It has no access point.
- It uses six full-duplex voice channels and one data channel.
- It allows up to 127 devices per network.
- It allows multiple networks in the same location.
- You can use encryption to make your data secure.
Here are the disadvantages of SWAP:
- It's not very fast (normally 1 Mbps).
- It has a limited range (75 to 125 ft / 23 to 38 m).
- It's not compatible with FHSS devices.
- Physical obstructions (walls, large metal objects) can interfere with communication.
- It's difficult to integrate into existing wired networks.
The actual wireless transceiver, with a small, integrated antenna, is built into an ISA, PCI or PCMCIA card. If you have a laptop computer, the PCMCIA card plugs directly into one of the PCMCIA slots. For desktop computers, you will either need a dedicated ISA or PCI HomeRF card, or a PCMCIA card with a special adapter. ISA and PCI adapters are inserted inside the computer and have a slot that is accessible from the back of your computer so you can plug in the PCMCIA card. USB adapters are external devices that you plug the PCMCIA card into and then connect to a USB port on the computer. Some of the HomeRF manufacturers sell kits that include the appropriate adapter along with the PCMCIA cards and installation software. Currently, because of the need to use dedicated cards, only computers can participate in a SWAP network. Printers and other peripheral devices need to be physically connected to a computer and shared as a resource by that computer.
In most cases, SWAP-based networks are point-to-point. Some manufacturers do offer access points as an option to increase the effective range of the wireless network, but they are not required equipment. Mainly because of this lack of an access point, HomeRF networks are significantly cheaper than the other viable wireless network, WECA's Wi-Fi. But the tradeoffs for cost are speed and distance. If you can set up a wired network using HomePNA or traditional Ethernet, you will get 10 to 100 times the speed for the same amount of money or less. However, unless you plan to send large amounts of data (like video) back and forth, SWAP speed is probably adequate for most home use, and the freedom of no wires can be quite appealing. Just remember that this is still a developing technology. |
WECA and Wi-Fi
The Wireless Ethrenet Compatibility Alliance (WECA) has gone in a completely different direction from HomeRF. Targeted more at office use than home networks, Wi-Fi (for "wireless fidelity", like Hi-Fi for "high fidelity" in audio equipment) is essentially a seal of approval that says the manufacturer's product is compliant with a variation of the IEEE 802.11 specification known as IEEE 802.11b . This specification drops FHSS and focuses on DSSS because of the higher data rate it can attain. Under 802.11b, devices communicate at a speed of 11 Mbps whenever possible. If signal strength or interference is disrupting data, the devices will drop back to 5.5 Mbps, then 2 Mbps and finally down to 1 Mbps. Though it may occasionally slow down, this keeps the network stable and very reliable.
Here are the advantages of Wi-Fi:
- It's fast (11 Mbps).
- It's reliable.
- It has a long range (1,000 ft / 305 m in open areas, 250 to 400 ft / 76 to 122 m in closed areas)
- It's easily integrated into existing wired-Ethernet networks.
- It's compatible with original 802.11 DSSS devices.
Here are the disadvantages:
- It's expensive.
- It requires an access point.
- It can be difficult to set up.
- Speed can fluctuate significantly.
Wi-Fi offers Ethernet speeds without the wires, but you pay for it. Access points vary greatly in cost, from about $300 to $1,400. Most access points have an integrated Ethernet controller to connect to an existing wired-Ethernet network. It also has an omni-directional antenna to receive the data transmitted by the wireless transceivers. Apple sells an inexpensive ($299 list) and easy-to-configure access point called Airport. Airport has to be connected to an Apple computer (iMac, PowerMac, iBook), but it will accept signals from any 802.11b-compatible wireless-network card, whether its PC or Mac-based.
Like HomeRF systems, the majority of Wi-Fi wireless transceivers available are in PCMCIA card form. But some manufacturers do offer PCI or ISA format cards, not just adapters. The cost per card ranges from $99 to more than $300. Because these products are not targeted at the home market, they are not typically sold in "do-it-yourself" kits. Instead, everything is a la carte , allowing customers to build a system that exactly meets their needs. |
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