Latest News

Why Wi-Fi?

Avoid tearing up walls and stringing wires with wireless Ethernet, or 802.11b Gadgets hed: Why Whi-Fi? dek: avoid tearing up walls and stringing wires with wireless Ethernet, or 802.11b. dek: HomeRF is aimed primarily at the home networking market. dek: you might be best off waiting a year for 5GHz products. by Ken Henningsen

In the past couple of years, computer wireless networking has seen rapid growth, and for reasons that aren’t hard to discern, this trend will only accelerate in the coming months and years. In enterprise and education settings, the portability of the ubiquitous laptop cries out for an equally portable networking scheme. And home and SOHO users increasingly have multiple computers, often including a laptop or two, that need access to each other and to a single telephone line or broadband modem. Wireless can be the easiest and most flexible way to meet these needs.

As with seemingly every new technology these days, two mutually incompatible wireless schemes are vying for your attention and your bucks–Wi-Fi and HomeRF. An emerging third, Bluetooth, isn’t a direct competitor; it is designed for much shorter ranges, meant to replace wired connections and IR links between nearby gadgets. All three share the unlicensed 2.4GHz band with many other devices, including microwave ovens, some industrial and medical equipment, and many cordless phones.

The technology with the longest pedigree, mostly in enterprise environments, is an 11Mbps system variously known as IEEE 802.11b, Wireless Ethernet and, most recently, Wi-Fi (for wireless fidelity). It is being pushed by the Wireless Ethernet Compatibility Alliance (WECA), a consortium of some 70 companies, including most of the big computer makers. Wi-Fi uses a transmission scheme called direct-sequence spread spectrum (DSSS), which reduces interference with and from other 2.4GHz devices by spreading its signal pseudorandomly through a relatively wide chunk of the band.

Wi-Fi’s arch-competitor is HomeRF, a relative upstart primarily aimed at the home networking market. It uses a different scheme called frequency-hopping spread spectrum (FHSS), and is promoted by its own association of 50-plus companies. Many of these are hedging their bets by producing or supporting Wi-Fi products as well. HomeRF is in the middle of a major upgrade, and there is no version-2 shipping product. So I’ll focus on Wi-Fi in this article and wait for some future slot to review HomeRF 2.0 products.

Both Wi-Fi and HomeRF can operate either in peer-to-peer (also called ad hoc) or infrastructure mode. The former creates a temporary network among all the wireless-equipped computers in range, let’s say a bunch of students with laptops, with no central control point. The latter uses one or more base stations, or access points (APs), to direct traffic and provide wireless gateways to a wired network. In a large wireless network, these APs automatically hand you off to one another in cell phone fashion. An AP can be either a computer set up to handle the infrastructure chores, or a standalone box. An advantage of a standalone system is that it draws relatively little power and can be economically left on (along with a connected cable or DSL modem, perhaps), to provide access to any computer that needs to get online.

Incidentally, neither DSSS nor FHSS conveys any inherent security benefits. Their spread-spectrum schemes will deter only the most amateurish of interception attempts. For that reason, both Wi-Fi and HomeRF support password protection and encryption, and use of these is even more important than on wired networks, given that you’re putting your data on the airwaves–albeit short-range ones.

To the batcave

I looked at two Wi-Fi systems, the Apple AirPort and the Farallon NetLINE/SkyLINE. Each consisted of a standalone AP ($299 for the AirPort and $300 for the NetLINE) and wireless cards for the networked computers ($99 for the AirPort and $150 for the SkyLINE). Both APs have Ethernet connectors for hooking them up to an existing network or to a cable or DSL modem. Additionally, the AirPort sports an internal 56K modem to support dial-up connections from anywhere on the network. Wireless interfaces come in three principal configurations from different vendors: PCMCIA cards (Type II or CardBus) for use in laptops and pre-configured desktops, PCI cards for desktops, and USB adapters. Wi-Fi-compliant devices can interoperate, and the Apple and Farallon units got along fine with each other, though the inevitable differences in software and terminology make mixing and matching more complex than sticking with one vendor.

In my testing, I assessed five principal characteristics: ease of setup and configuration, usable range under various conditions, data transfer speeds, tolerance of outside interference, and interference with other devices. For the interference testing, I used several other common 2.4GHz devices, including a full-sized microwave oven and three different telephones: one fixed-channel model and two FHSS jobs. One of the latter had dual “diversity” antennas, which are supposed to improve range by dynamically selecting the antenna with the best signal.

I also have a 2.4GHz fixed-channel analog A/V sender (sold by Radio Shack and, among others) that transmits the TV signal from a bedroom TiVo unit to my office TV. I tested the systems on my three Macs (a new G4 desktop and two older PCMCIA-equipped PowerBooks), but my experience should be transferable to PC installations except for the details of installation and configuration. Mac users should be sure that drivers and application software are provided for the system they’re considering, and that Mac versions aren’t available for all products.

Installation and setup of both the Apple and Farallon systems was straightforward, and both worked with each other right out of the box. That’s not to say problems can’t arise; computer networking is tricky work, and wireless adds another layer of complexity. The utilities with these devices include a bewildering array of configuration options and arcane terms, and if you’re hooking into an existing enterprise network or have other special circumstances, you may need to dive into the manuals or punt to your network administrator. Fortunately, the typical home or small-business user usually can avoid straying off the beaten path.

Range is perhaps the toughest variable to nail down. It depends on a host of factors, and will differ with every installation. In my setup, I found the typical 150-foot indoor claim to be optimistic. I could usually connect from anywhere in my house (up to about 50 feet), but sometimes only if I oriented my laptop in a particular direction. With the laptop outdoors, I was able to connect on the side of the house closest to the AP, but not on the other side–my aluminum siding no doubt had something to do with this. In general, the higher you can mount the AP, the better your range will be. Some APs (though neither of those I tested) have diversity antennas, which may improve their range. This is a purchase for which you definitely should get a trial period in case it doesn’t meet the demands of your environment.

To test real-world speed, I copied a folder of a variety of files totaling 12.5MB–a nice, round figure for timing transfers. I also tried playing QuickTime movie and MP3 files over the wireless link to see how it handled streaming video and audio. With no other traffic, my observed rates between two wireless computers ranged from 1.0 to 1.3Mbps. This sounds disappointing for a nominal 11Mbps system, but it’s not a lot slower than normal throughput on a standard 10Mbps wired 10BaseT Ethernet connection (over which I measured 1.7 to 2.0Mbps for the same transfer). There’s obviously a lot of overhead involved with the Ethernet protocol, with wireless adding a layer of its own. I also found that losing the wireless connection, even temporarily, halted a data transfer, requiring that I restart it from scratch once the connection was re-established.

Even streaming audio/video files with bit rates well below the above speeds stuttered occasionally, probably because of packet errors and retries due to interference. For smooth playback, such files really need to be downloaded and then played, or buffered by the player and played back on a delayed basis. I did a lot of Web surfing via my cable modem, which typically provides a throughput of 300 to 500Kbps. As long as I had a wireless signal at all, download speeds seemed to be roughly equivalent to a wired connection (this is not surprising, given that my lightly loaded network ran at three times the speed of the cable modem). Simultaneously transferring files between a couple of networked computers and downloading a large file from the Internet substantially slowed down the network transfer but not the Internet download, apparently due to a priority scheme. As with file transfers, losing the wireless connection meant having to manually restart a Web page download, albeit from the point where it quit.

Interference from and with other 2.4GHz devices can be the most serious impediment to wireless networking, especially in dense environments like apartment buildings. If you get a 2.4GHz cordless phone, definitely go for a spread-spectrum model, preferably one with dual antennas. Only the high-end diversity-antenna model seemed totally unfazed by the activity going on nearby; the single-channel phone was nearly unusable. None of the phones seemed to have any noticeable effect on the Wi-Fi network’s performance, though I suspect they caused occasional lost packets. Incidentally, my 900MHz spread-spectrum phone and the network were totally oblivious to each other; this could be a better phone solution if you want a wireless network.

My microwave oven didn’t have much effect on the network unless I was trying to connect from a laptop very close to it while it was running. Microwave interference is both pulsed and swept in a full circle, which makes it intermittent and fairly easily overcome with spread-spectrum technology. Also, the more food there is in the oven, the more any interfering radiation is absorbed. If you’re in an apartment building and surrounded by microwave ovens, however, you might experience some network degradation at meal and popcorn time. Also, beware if you live near a hospital; devices like diathermy machines can create a lot of 2.4GHz interference.

The one device that absolutely didn’t get along with the Wi-Fi network was my A/V sender. Supplying full-motion video and stereo audio that’s virtually indistinguishable from the wired source, it obviously needs a lot of bandwidth. It has four selectable channels, letting several video senders coexist without interference, but all but one of these brought the Wi-Fi network to its knees, first causing a sharp spike in noise level and then a total loss of signal. On its noninterfering channel, the A/V sender didn’t seem to bother the network, but the network caused rolling video noise bars and audio static on every one of the sender’s channels (as did my microwave and all of the 2.4GHz phones, for that matter). Until somebody comes up with a spread-spectrum A/V sender, don’t plan to use any other 2.4GHz devices. Fortunately, A/V senders aren’t all that common, but if your condo neighbor has one, you’ll be in for some conflict resolution if you set up a wireless network.

Bottom line: Like all wireless technologies, Wi-Fi is imperfect, and range and interference issues may be frustrating in some situations-or may become so as 2.4GHz devices proliferate. However, if it works in your environment, there’s something intoxicating about being able to sit down with your laptop just about anywhere in the house or yard and hit the Internet or your desktop computer and its resources. The price of this power isn’t all that high, and it’s dropping.

If the current Wi-Fi technology doesn’t work for you, or you want to hedge your bets, watch for the 5GHz stuff coming out next year. It will be incompatible with current 2.4GHz products (though some vendors are talking about dual-band units), but it will be both much faster and situated in a much less crowded chunk of the radio spectrum-at least for a while.

Leave a comment

seks shop - izolasyon
basic theory test book basic theory test