Loosely coupled

Wireless networking: The ties that don't bind.

Maury Wright, Executive Editor -- CommVerge, 4/1/2000

Imagine life without cordless phones. I don't think any of us wants to return to those days. Sure, I still use a wired phone when I'm chained to the desk in my home office. But otherwise, my family sticks to the cordless. In fact, it now seems inconceivable that every phone used to have one of those dangling, tangling cords. In a short time, I expect we might feel the same way when we think back to the days when we actually used wires to connect our computers. For I have discovered the luxury of a wireless LAN (WLAN).

I now perform Internet research on my patio. I catch up on email while watching the ball game on Sunday afternoon. And while it's no Walkman, my WLAN-equipped notebook offers a portable way to listen to Internet radio broadcasts that my trusty AM/FM unit won't tune in anytime soon. The potential convergence applications are endless. I can envision plugging an IP (Internet protocol) telephone into my WLAN connected notebook, and someday video will traverse the same airwaves. I'm sold.

I believe WLANs stand poised to become the most popular flavor of the broadly promoted home-networking technologies. The attraction for homes will be the elimination of the need to install LAN wiring. Several technologies (see sidebar "Crossed wires "), including power- and phone-line LANs, attempt to address this consumer market. Wireless LANs, however, offer far more—freeing you to move computers anywhere on an ad hoc basis, and as I've learned in working with Proxim's Symphony product, to move a notebook about without severing your LAN link.

WLANs aren't new. Companies such as Proxim and Lucent have sold such products for more than five years. Until now, however, a combination of interrelated factors has relegated the technology to niche applications. For starters, the technology lags Ethernet in terms of data rate. In addition, the computer industry took some time to agree on WLAN standards. Even when the IEEE 802.11 standard won acceptance, it still offered several conflicting options for its so-called physical layer—the actual hardware that transmits and receives the signal. This confusion slowed market acceptance and therefore kept prices high throughout much of the 1990s, just as uncertainty over Ethernet, Token Ring, StarLAN, and other options had slowed the acceptance of wired LANs in the 1980s.

It didn't help that the wireless-LAN physical layer—essentially a DSP engine plus a radio transceiver—costs more to implement than a wired-LAN transceiver. For instance, around five years ago WLAN network interface cards (NICs) sold for more than $500, yet moved data only 10 to 20 percent as fast as the 10-Mbit/sec data rate of standard Ethernet cards, which often sold for as little as $50. Making matters worse, WLAN users often need wireless access points (WAPs), devices that let them link WLANs to traditional LANs or help them construct multiple-cell WLANs that have greater range and higher capacity. These WAPs have sold for as much as $2000.

Horses for courses

With prices so high relative to Ethernet, WLANs found only limited favor, mostly in the business community. In fact, only companies with specific reasons not to use standard Ethernet opted for wireless. For example, restaurants deployed WLANs to equip food servers with remote order-input pads. By speeding the ordering process, they increased customer turnover, thereby boosting sales and justifying the high-cost technology. WLANs have also been used in hostile environments such as factories where wiring is impractical, in historically significant buildings where the walls can't be torn up to install wires, and on forklifts that rove through large warehouses. However, WLAN deployment has been limited in exactly the market that could cause volumes to skyrocket: notebooks for roaming professionals.

Today, the future looks much brighter. Sales are exploding in the business world, and that success is leading vendors to address the small office and home markets. Over the course of the last year, WLAN NICs have dropped to under $200, and the push is on to reach $100. At that magical price, many users might opt for wireless. WAP prices have dropped as well, with business units under $1000 and early home products under $500.

I'm not ready to declare that the hurdles to WLAN success are gone. But clearly they are much lower than even a year ago. New WLAN products are not only cheaper, but also faster. Lucent's just-announced Orinoco family and 3Com's AirConnect family operate at 11 Mbits/sec, based on the IEEE 802.11b standard (see "Wireless wars" and "Hearth and LAN"). While much of the business world has moved to 100-Mbit/sec wired Ethernet, an 11-Mbit/sec wireless alternative will serve quite well in many applications. In fact, it can theoretically exceed baseline Ethernet performance.

Last year, given the optimistic upturn in the WLAN market, and the reasonable prices, I started thinking about adding wireless capabilities to my little computing universe. And that led me to reexamine home LAN technologies and markets in general.

Multi-PC family

My LAN is probably more complex than that of the typical small office, so in some ways my experience is typical of what offices incur. I have a cable modem and at times as many as five systems that need to share that link. I've got two linked Netgear 10BaseT (10-Mbit/sec) Ethernet hubs in different parts of the house. Over the months that I've used a WLAN, I've relied on both software and hardware techniques for sharing the broadband connection (see the January and March editions of Inside the Digital Den ).

On the other hand, I'm not all that different from many homeowners in terms of motivation. I wanted mobile Internet access and a LAN link to my notebook PC. Some families may find that standard Ethernet or one of the other home LANs fits their needs better than a WLAN. I'm not ready to abandon my Ethernet wiring yet, but I knew I wanted the flexibility to add a couple of wireless nodes. My son's PC was going to be relocated temporarily to a different room that lacks installed Ethernet wires. Plus, I've long wanted the flexibility of a patio connection—without my wife complaining when I run a Category-5 cable out through the doorway.

As I surveyed the market in the late summer and early fall, I saw limited choices. Business-grade products in both the frequency-hopping and direct-sequence spread-spectrum flavors were abundant, but too pricey for home. (If those technical terms caused your eyes to glaze over, see the sidebar "Spread spectrum uncovered.") Diamond Multimedia offered a proprietary WLAN product for the SOHO market. The clear leader for SOHO, however, was Proxim's Symphony.

Essentially a stripped down version of Proxim's higher-end RangeLAN product, the Symphony family was the first to sport a consumer-friendly price tag. The products operate at 1.6 Mbits/sec and includes all of the pieces necessary to handle most SOHO chores. For desktops, you can buy a NIC in add-in card form (either ISA or PCI) for $129. For notebooks, the $149 NIC comes in PC-Card form.

If you want multiple PCs to share an existing dial-up modem connection to the Internet, all you need is a NIC for each system. Symphony includes the software necessary to share the connection. Obviously, the PC with the modem must remain on in order for the other nodes to access the Internet. Alternatively, the Symphony family includes a $249 stand-alone modem that wirelessly connects to all your Symphony-equipped systems, eliminating the need for that always-on PC. Finally, a $399 Ethernet bridge comes in handy for users who need to fasten an existing Ethernet LAN to a Symphony WLAN and/or share an always-on broadband link, such as a cable modem.

Plug and play

I initially worked with one PCI card and one PC Card, since the Ethernet bridge was temporarily out of stock. The difficulty of installing and using a product like Symphony varies directly with the complexity of your home or office LAN. The same is true of products that use your existing phone lines as LAN links (see sidebar, "Crossed wires"). In either case, anyone who can open a PC and install a PCI card can probably connect a handful of nodes in a peer-to-peer LAN and share a modem-based Internet connection. Moreover, once you have connected PCs, you can share files and printers. Software installation is trivial. The vendors have molded the installation routines precisely for the intended Internet-sharing application.

This simple, scripted installation based on a single application is no doubt a blessing for novice users. However, in some cases (Symphony excluded) it's a curse for those of us with more complex goals. Please allow me to briefly rant. When working with the Intel AnyPoint HomePNA product, I found that my standard Ethernet card and the Intel HomePNA card could not coexist in my PC. Intel's software simply asked me to remove the offending card and start over, even though there's no technical reason for such a "this-town's-not-big-enough-for-the-both-of-us" stance. The Intel software simply prevents you from using their product in a manner different from what Intel considers typical. Of course, I suspect that one could find the appropriate software driver, manually install the driver, manually configure the AnyPoint adapter, and make things work. But in this case, Intel went too far in protecting us from ourselves.

That's the end of my rant. But it brings up something I think Proxim should be lauded for. The company has done a very good job of creating a simple installation routine, yet still granting experienced users the freedom to configure a system as they see fit. The Symphony NICs come with software that's geared to a simple LAN setup sharing a dial-up connection or using the Symphony cordless modem. But the instructions clearly direct users with more elaborate plans to disregard the NIC software and opt instead for the software that ships with the Ethernet bridge.

As you're no doubt beginning to grasp, once you go beyond the standard install, you need to understand a little about LANs. For example, the Symphony bridge supports a number of configurations. For more details on my experiences with Symphony, see the sidebar "Advanced schemes."

Qualified success

Having used Symphony for a number of months, I would recommend the product, albeit with some qualifications. If you simply want to provide Internet access to some wireless nodes, it works great. The advertised 1.6-Mbit/sec data rate actually tops out at less than half that. But even 500 kbits/sec for Internet connectivity is better than any dial-up connection and equal to the real throughput users experience on a corporate LAN. Anyway, even though a cable modem can theoretically go faster, traffic on the Internet often limits the actual speed to less than Symphony's capabilities.

If you want to use a WLAN for heavy file sharing and typical office-LAN duty, Symphony may not be for you. I print Internet pages via my Symphony link all the time, and I frequently use Symphony to move small files. But when I get ready to leave on a trip and I need to perform major file movements to synchronize my desktop with my notebook, I replace the Symphony card with a wired-Ethernet card. Two problems with big transfers make this action necessary. First, Symphony's low data rate means transfers take quite a while. You might think, "No problem—just leave the transfer running through dinner or overnight." But Windows does funny things when errors or even duplicate files crop up during file-copy operations. At best you have to tell Windows to replace everything (all duplicate files and directories). At worst, an error interrupts the copy process and you have to start over from square one.

I give Proxim kudos for recognizing that users might want to switch back and forth between Symphony and regular Ethernet frequently. Symphony's Maestro feature lets you accomplish this. For example, if you want to switch to Ethernet mode, you simply fire up Maestro and tell it so. Shortly after you issue the command, the notebook shuts down. You slap in your standard Ethernet card, boot the machine back up, and you're ready for Ethernet operation. Performing the same process in reverse returns you to wireless mode.

I yearn

Although my current setup is pretty slick, I still long for a faster WLAN link, one that could permanently replace my Ethernet card for my notebook. Luckily, this is probably just around the corner. Already 11-Mbit/sec products are rolling out at Symphony-like prices. Moreover, Proxim now offers business products at speeds up to 25 Mbits/sec.

It appears, however, that the Wireless Ethernet Compatibility Alliance (WECA, www.wirelessethernet.org ) will be the standard of choice for Ethernet speeds in office, SOHO, and perhaps home applications. Apple's consumer-oriented AirPort, for example, is derived from the WECA and IEEE 802.11b standards. AirPort got off to a rough start with numerous configuration issues—once again pointing out the importance of well-conceived manuals and installation routines for the consumer. Compaq has also endorsed WECA despite the fact that Compaq already supports Symphony on some WinCE systems.

Expect consumer-priced WECA products from Lucent, 3Com, and others shortly. I had hoped to test one for this article, but the companies are still trying to make the consumer products as user friendly as possible. 

Although WECA appears to be in a dominant position, differing opinions on WLAN technologies could still slow market penetration in homes. The Proxim and Lucent/Intersil camps have never agreed on the choice of frequency-hopping or direct-sequence technologies. While WECA has chosen the latter, Proxim and the HomeRF Working Group (www.homerf.org) continue to champion the former, claiming it will be less expensive. In general, the proponents of frequency hopping have been hamstrung by FCC rules in their attempts to reach Ethernet speeds. The HomeRF group hopes those roadblocks will fall this spring, leading to a jump from 2 Mbits/sec to 8 Mbits/sec. Proxim has vowed that the next iteration of Symphony will comply with the HomeRF standard and aims to further boost speed down the road.

Meanwhile, HomeRF has defined a standard called SWAP (shared wireless access protocol), which allows computers, wireless phones, and other devices such as fax machines to share the same frequency spectrum in homes. Ahead, SWAP will probably carry audio and video as well. Before we realize the ultimate in WLANs for the home, either WECA must give way to HomeRF for homes, or WECA must add SWAP-like features.

Still, I think WLAN offers the brightest future in the home-LAN space. Prices are headed down to such levels that a phone-line product won't have an insurmountable advantage. WLANs offer the ultimate in flexibility. WLAN usage is spreading in businesses. And WLANs offer a possible technology for public LAN access in facilities like airports. In the future, you could use a single WLAN card in your notebook to access the net at home, at work, and in an airport or convention center. Today's business-grade products are rock solid. If vendors can approach that level of reliability with home products, then folks, we have a winner.

Crossed wires Until about two years ago, the term "home networking" typically referred to technologies that might someday provide home automation, such as lighting control. Now, however, home LANs are hot. According to market analysts, huge numbers of families own multiple PCs. Sharing an Internet connection seems to be the killer application that will drive home LAN deployment. PC-industry leaders such as Microsoft and Intel have been preaching the "no new wires" mantra regarding home LANs for several years now. "No new wires" means either wireless technology or something that uses the home's existing power lines or phone lines to carry LAN signals. I didn't buy "no new wires" at first. I had long ago strung traditional Ethernet cables (thin coax and Category-5) to a number of rooms in my house. I always realized that wireless or no-new-wires would be better, but hey, Ethernet NICs now go for as little as $10. Moreover, I always thought that 10 Mbits/sec would be a minimum acceptable data rate, even for home users. And I doubted that wireless, phone-line, or power-line LANs would hit that rate anytime soon at consumer prices. In fact, two years ago I would have said that WLANs were the least plausible home-LAN alternative. Intel was making a huge push for power-line networking, and a number of companies led by Microsoft and Tut Systems were championing phone-line alternatives. Intel later joined that group too. The phone-line folks have made the most noise and have the greatest number of products on the market Despite the hype, I consider power- and phone-line technologies underwhelming to date. So far, no one has shipped a power-line product that operates faster than 100 kbits/sec at a reasonable price. But the participants continue to make noise (see "Alternating currents"). And a new player called Power Trunk recently claimed it will deliver 25-Mbit/sec rates. All I can say is, "show me the data." As for phone-line products, I recently helped evaluate some as part of a project for sister publication EDN (see, "Home-network contenders steer a collision course" at www.ednmag.com). EDN Technical Editor Warren Webb and I found that the 1-Mbit/sec phone-line products worked, with limitations. But reader response to that article indicated that the 10-Mbit/sec products rarely work with the typical spider-web of phone wires already installed within homes. Don't misunderstand. Wireless alternatives aren't perfect either. For example, reader feedback indicates that the proprietary WLAN sold by Diamond has real problems when the PCs are spread far apart or separated by walls. Even the Proxim product I'm using has a few problems, which I detail in the main article. However, I believe vendors will iron these problems out. Eventually, a single flavor of wireless Ethernet will come to dominate the home LAN space.

Spread spectrum uncovered It's likely that you've seen the words "spread spectrum" used in product hype, even if you don't have a real reason to know or understand anything about this mysterious communication scheme. In fairness, spread-spectrum technology has resulted in improvements in wireless phones, LANs, and radios. But spread spectrum is a general term that applies to a number of different ways to implement wireless links. Lets take a quick tour of the most popular implementations. We'll see where they fit in the wireless world, as well as where you can go to find the real technical details if you need or want them. Generally, spread spectrum refers to using a wider frequency band than is actually necessary to transmit an RF signal. By using the wider band, the scheme aims to ensure reliable communications even in the face of RF noise and interference. As you might guess, there are several ways to artificially broaden the transmission band. Frequency-hopping spread spectrum (FHSS) is perhaps the simplest approach to a spread band. In an FHSS system the transmitter uses a traditional narrow-band communications scheme. But the transmitter sends a short burst of data at one frequency, then hops to another frequency for another burst, and another, and another. The transmitter and receiver move around the wide band using a predetermined hopping sequence. In fact, multiple transmitter/receiver pairs can operate simultaneously in the same wide band by using different hopping sequences. Occasionally, transmissions will collide on the same frequency, or interference from a source like a microwave oven will interfere with the burst sent during a specific hop. The scheme simply requires retransmission of data that doesn't get through. The amount of interference and the number of transmitter/receiver pairs in the frequency band determine how often bursts get corrupted and in turn what percentage of the maximum data rate you can realize. The IEEE 802.11 standard for wireless LANs (WLANs) specifies FHSS as one of the RF options for the so-called physical layer (PHY). In the 2.4-GHz band, 802.11 FHSS WLANs can deliver 1- or 2-Mbit/sec data rates. Presumably, the scheme could support rates up to 8 to 10 Mbits/sec, but FCC rules prevent the use of the slightly wider bands that would enable this acceleration. FHSS supporters are lobbying the FCC to change this rule, which they consider arbitrary and unnecessary. Proxim has been a leading proponent of FHSS technology and the leading vendor of FHSS WLAN products. Proxim's RangeLAN and Symphony products are based on FHSS, although only the former meets the 802.11 standard. The presently proprietary Symphony product family will transition to the HomeRF standard, which is essentially a defeatured flavor of 802.11 FHSS. Proxim has a host of white papers on WLANs and FHSS technology at www.proxim.com/wireless/index.shtml. Direct-sequence spread spectrum (DSSS) offers a second approach to a wide band, and is the second PHY option defined under 802.11. Most data-transmission schemes, be they for a wired modem or a WLAN or a digital cell phone, break the data stream into a sequence of symbols. A single symbol represents multiple bits. The so-called modulation scheme--examples include FSK (frequency shift keying) and QAM (quadrature amplitude modulation)--determines just how many bits a single symbol can represent. Therefore, you can see that the modulation scheme is a key factor in determining the maximum data rate that can be conveyed in a specific frequency band. DSSS transmitters multiply each sequential symbol by a binary sequence called a chip sequence. In simpler terms, rather than transmitting each symbol a single time, the DSSS radio transmits it multiple times. For example, an 802.11 DSSS radio uses an 11-bit chip sequence (also called a pseudorandom noise sequence); it transmits each symbol 11 times, with each instance being referred to as a chip. Since both the transmitter and receiver know the chip sequence, the receiver can decipher the incoming symbol even if interference mangles some of the chips. The length of the chip sequence determines how effectively the scheme can function in the face of noise, how complex the signal-processing task is for the receiver, and even how secure the link is. First-generation 802.11 DSSS radios deliver 2 Mbits/sec in the 2.4-GHz band with a fallback to 1 Mbit/sec possible in noisy environments. The newer second-generation 802.11b standard ups the maximum rate to 11 Mbits/sec while allowing backward compatibility with 2-Mbit/sec radios. Generally speaking, DSSS is considered technically superior to FHSS, but it also costs more in terms of signal-processing horsepower and transmission power, and therefore dollars and battery power. Lucent Technologies and Intersil have been the chief champions of DSSS technology. The new Wireless Ethernet Compatibility Alliance (WECA) has endorsed 802.11b as essentially wireless Ethernet (you can find DSSS details at www.wi-fi.com/whitepapers.asp and www.intersil.com/prism/wirelessb.asp). If I've kept your attention to this point, I may as well conclude by placing digital cell phones in the picture, given that they are the most common incarnation of spread-spectrum technology. Neither TDMA (time division multiple access) nor TDMA-based GSM (global system for mobile communication) phones use spread-spectrum technology, but CDMA (code division multiple access) phones do. CDMA is based on DSSS. To allow multiple conversations in a cell, each CDMA phone gets assigned a unique chip sequence for each call. Clearly, a high number of active calls in a cell will result in significant interference, causing symbols to be dropped and voice quality to degrade. Therefore, people refer to CDMA phones as "interference limited." TDMA and GSM phones can't support as many calls per cell as CDMA phones, but with TDMA all connections typically sound the same.

Advanced schemes The Symphony bridge supports a number of advanced configurations. It can connect directly to a DSL or cable modem and handle Network Address Translation (NAT) functions, which allows up to eight PCs to wirelessly share a single IP address. But I already had NAT software in place when I first started working with the bridge. Moreover, I wanted to maintain the ability to share my cable modem among several wired nodes connected to my hubs, while also adding some new wireless nodes. The Symphony bridge can operate in a mode where it only provides transparent bridging between two LANs. In simpler terms, the nodes on the wired and wireless LANs appear to be on a single LAN when the Symphony bridge is connected at one of my hubs. The manual also points out that the bridge can perform both NAT and transparent bridging simultaneously. In fact, this is the default setting. But I suspect that most users should avoid that setting because of potential security issues that accompany an always-on broadband connection. When I first installed the Symphony bridge, I was using static IP addresses that were set in a range suggested by the Sygate NAT software I was using on my gateway machine. I had to manually change the IP address settings in the bridge. The unit comes set for DHCP (dynamic host control protocol) operation, which means some entity on the network dynamically provides IP addresses to each node. Neither my cable service provider nor the Sygate software had a DHCP agent, but setting the IP addresses is relatively easy. I assigned one address to the bridge, performing that configuration via one of the wirelessly connected PCs. I also had to configure each of the wirelessly connected PCs with its own IP address and with other information such as name-server and gateway addresses. Later, I changed my configuration significantly. I replaced the software NAT gateway that resided on one machine with a dedicated device, the WebRamp 700s firewall, router, and NAT gateway from Ramp Networks. The WebRamp 700s includes a DHCP agent. Once you configure the 700s with its IP address, the ISP's name-server address, and the ISP's gateway address, the 700s can dynamically configure the client nodes. In fact, with only a couple of glitches I changed both my wired and wireless LANs to DHCP operation. I had to change a single setting on every machine to use DHCP, and I had to use one of the wireless nodes to change the setting in the Symphony bridge. I'd offer just one word of caution. After making such a change, power down everything—every PC, every hub, the bridge, and the cable modem--to erase any chance of IP gremlins living on in one of the LAN devices.