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Next-Generation Wireless LAN

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From the second that Starbucks announced it would be offering wireless LAN connectivity in select outlets, proponents of the technology could say definitively that the technology had matured. Shortly thereafter, other companies, hotels, and airports started setting up wireless "hotspots" at which you could, for a fee, use their Internet connection on your wireless-enabled laptop. Up to that point, wireless had "Forest Gump'ed" its way into corporations. But now that there is an established consumer market, we can look forward to the next generations of wireless LANs.

In this article, I will define the current wireless LAN technology: the IEEE802.11b standard. Using this foundation, I'll look at the next versions of wireless communications that are now coming to market and where it's best to use wireless.

What Did We Do Before?

In AS/400 shops, the most common use of wireless was bar code scanning in warehouse environments. Because of the low bandwidth constraints of the 5250 data stream, this was an ideal application of wireless technology. However, companies had to license frequencies from governing bodies such as the FCC. The wireless handheld barcode scanners were proprietary to the antenna receiving the information. While this situation was standard in AS/400 shops, the IT industry was moving toward open systems, and the FCC was opening the 2.4 GHz frequency spectrum.

Dawn of a New Day

In 1997, the Institute of Electrical and Electronics Engineers (IEEE) approved the 802.11 wireless standard, which then prompted the 1999 ratification of the 802.11b standard. The beauty of this standard is that it provides 11 Mbps communication and vendor interoperability over the unlicensed 2.4 GHz frequency. This standard--known as "wireless Ethernet," "Wi-Fi," or "802.11 High Rate"--defined the access points (APs) in the air and the wireless Ethernet cards that were placed in client computers and laptops.

Parallel to this development, vendors were developing LAN-to-LAN wireless links that operated similarly to the 802.11b standard but were still proprietary. They could, however, travel up to 20 miles with the proper positioning and antenna configuration. These links provided 11 Mbps transmissions as well and offered a short return on investment compared to the cost of leasing a T1 line.

When the industry proved that standards-based wireless communication was possible, the consumer market started seeing the benefits. Companies like Linksys, D-Link, 3Com, Nortel, and Cisco now offer wireless Ethernet for the home. For around $200, you can purchase a broadband router that connects to your high-speed DSL or cable Internet connection, provides several wired Ethernet ports, and acts as an 802.11b AP so that you do not have to run wires throughout your house. You can now walk around your house with your laptop and stay connected to your high-speed Internet connection. And your kids can do the same thing at the same time!

802.11b Details

Wireless Ethernet is the means by which devices can have a wireless network card installed and, through a wireless AP, communicate with either other wireless devices or wired devices on a network or a WAN. The wireless network card can be a PCMCIA, PCI, ISA, or USB device that emulates an Ethernet connection. The antenna on the card transmits on the 2.4 GHz open frequency to the AP, which typically sits in the ceiling. The AP can communicate with the corporate network either by being physically wired to it or by bouncing to another AP that is wired to the network.

The standard also takes into account the possibility of having multiple APs in a single facility. So if you want to travel with your wireless barcode scanner in a large warehouse, you will automatically roam to the strongest AP. To accomplish this, the AP sends out a beacon approximately 10 times a second that lets the wireless network cards know the AP's parameters. If the beacon becomes weak, the network card starts looking for an AP with a stronger signal.

APs and wireless network cards can transmit at four data rates: 11 Mbps, 5.5 Mbps, 2.0 Mpbs, and 1.0 Mpbs. Transmission will start at 11 Mbps; as signal strength degrades, transmission will fall back to slower speeds. Before this happens, however, there is a check for other APs in the area that can transmit successfully at 11 Mbps.

Now for the important question: How far will the signal transmit? The standard says that in an office environment where the signal has to penetrate three walls, you can transmit at 11 Mbps from 100 feet away from the AP. At 1 Mbps, you can be 330 feet away. In an open or outdoor environment, where there are fewer obstructions, you can be 300 feet away at 11 Mbps and up to 1,500 feet away at 1 Mbps.

Implementation Tips

Specifications are based upon the standards community and some tweaking done by vendors. Because vendor specifications vary, the equipment you purchase (such as antennas) will greatly affect your range and, consequently, your coverage.

The rule of thumb from wireless LAN companies is that for every 25,000 square feet (SF) covered, you should have a single AP. I recommend one for every 15,000 SF. Our building is 86,000 SF, and we've implemented six APs. On each AP, there are two 12-decibel (db), omni-directional, outdoor-rated antennas. With this upgraded equipment, we can be more than 330 feet from the AP and still transmit at full strength.

Another benefit of upgrading to top-of-the-line antennas is that transmissions can penetrate concrete walls and floors, providing multipoint redundancy. No matter where you are in the building, if the AP closest to you fails, you have at least one other AP that can pick up the signal. So you are never affected by an outage.

With antenna upgrades, you can customize how the signals are dispersed. If you want a coverage area of 35 degrees from the front of the antenna but not through the back of the antenna because it's mounted on an outer wall, you can have that. There are many options, so I recommend that you choose a company that specializes in wireless installs to determine the proper antenna for your installation.

Another benefit that current wireless LAN APs offer is the ability to run power and network connectivity over the same cable. Previously, you had to run both a network cable and a power cable to the AP wherever in the ceiling it was. The power cable had to terminate near a UPS so that it was protected from power surges and brown/blackouts. Now, there are adapters that place the electrical signal on the network cable and then break it out at the AP. Because your Ethernet hubs and switches are typically on power protection equipment, it's easy to extend that protection to your AP.

Dawn of Next Generation

Statistics from some research organizations state that wireless installations increased by 1.5 million in 2001. With this type of penetration, the industry is now looking for what's next. The common thread has always been an increase in speed. With all Ethernet protocols, the published rate is significantly higher than the amount of data you can actually transmit. In the wireless environment, approximately 40% of the bandwidth is used for overhead, resulting in a maximum of 6 Mbps for data transmission.

Two protocols are currently emerging. One offers higher bandwidth and operates in the 5 GHz frequency, removing the possibility for backward-compatibility. The other provides backward-compatibility with 802.11b, but it's not highly adopted. Neither provides a friendly naming convention!

802.11a

The higher the frequency, the more susceptible to interference it is. If you are sitting on your front porch cursing the kid that drives by with loud music, you rarely hear the vocals or high notes. You'll just hear the pounding of the bass. This is because bass is a lower frequency, which travels better and experiences less interference.

Note that 802.11a was actually proposed prior to 802.11b. The reason that it took so long to ratify is that 802.11b uses simple Direct Sequence Spread Spectrum (DSSS). The 802.11a protocol uses the more complicated Orthogonal Frequency Division Multiplexing (OFDM), which held up the ratification process. OFDM compensates for the additional interference caused by the higher frequency and allows close to the same distances observed with 802.11b.

The 802.11a protocol provides the facility for 54 Mbps of bandwidth. This is almost a fivefold increase over 802.11b. In addition, 11 channels can be operated simultaneously without causing interference. 802.11b also provides 11 channels but the cross-talk between channels means that only three channels can operate over the same air space. If you have 33 wireless computers, it is preferable to have three of them operating over 11 non-interfering channels rather than 11 operating over three channels.

In addition, 802.11a provides seven fallback rates as opposed to the three provided with 802.11b. Being able to transmit at 54 Mbps will rarely occur. You will be required to have a short, unobstructed path to the AP. If not, then the rate will fall back to an appropriate bandwidth.

Antennas are designed for a specific frequency. If you purchase an 802.11a AP, then the antenna is designed for 5GHz transmission. Because of this limitation, your existing 802.11b infrastructure will not communicate with an upgrade to 802.11a. You will have to run both in parallel or perform a cutthroat implementation.

802.11g

802.11g addresses 802.11a's inability to be backward-compatible. It operates in the heavily used 2.4 GHz frequency and increases both the bandwidth and the distance available by using OFDM. The bandwidth is the same as 802.11a, 54 Mbps. But because 802.11g operates in the same frequency as 802.11b, you can have both types of wireless transmissions operating on the same AP.

The combination of low frequency and OFDM in 802.11g results in better coverage than 802.11a provides. Initial guesses are that the distance increase is double 802.11b's standard, which means that for every 75,000 SF, you'll only need one AP. But if you have devices that are still on 802.11b, you'll need APs every 25,000 SF.

Another limitation of 802.11g is that it has only three channels. This means that only three devices can transmit at one time. If you architect your wireless devices correctly, this should not be a problem. I'll get into that in the Where to Use Wireless section.

Security

The big weakness with wireless Ethernet has been security. Originally, there was no encryption standard, so a hacker could simply listen to the transmissions as they flowed through the air in clear text. Wired Equivalency Protocol (WEP) addressed this problem. Using either 40- or 128-bit keys, WEP encrypts transmissions on the fly and attempts to provide the same security as a wired network. The problem, however, is that off-the-shelf wired networks do not provide an abundance of security. In fact, there are utilities on the Internet right now that allow would-be hackers to quickly break the encryption and access your internal network from your wireless network. And if your antennas are strong enough, they could do this from your parking lot!

Wireless hardware vendors are trying to overcome this deficiency by selling additional security software. While this will be beneficial to the end user community, it doesn't address the problem from a standards point of view. A new standard called Temporal Key Integrity Protocol (TKIP) is coming out soon. TKIP is a revision of WEP. However, some industry insiders are saying that it is actually less secure than the original WEP.

If security is of paramount concern, speak with your Value Added Reseller about what options are available for the hardware you are purchasing. For example, consider Cisco's Secure ACS software. While initially providing Access, Authority, and Accounting for its firewall products, Version 2.6 started providing the same three AAA's for Cisco wireless equipment. Before gaining access to the network, a wireless client must be authenticated first--a big step toward providing a secure wireless environment.

Which Standard?

Wireless provides yet another scenario in which consumers are pitted against each other in a race to see which standard will survive. While I've provided enough information to enable you to pick which standard suits you, I'll provide my opinions as well.

The 802.11g standard does not appear to be close to ratification. While there are already manufacturers producing 802.11a equipment, 802.11g vendors are few and far between. This is unfortunate for companies that have a heavy investment in 802.11b and want the speed upgrade with the promise of parallelism. If you are in this boat, I recommend that you wait six to twelve months to see if the 802.11g standard catches on.

For those of you evaluating wireless with nothing yet implemented, I would definitely go for 802.11a. With many vendors producing products for this standard, it's a pretty safe bet that there will be continued support into the future.

Where to Use Wireless

To wrap things up, something should be said about when and when not to use wireless. I saw a television commercial that depicted an office where there are no wires. This is not a reality with either the technology currently available or the technology of the near future.

At the beginning of this article, I mentioned 5250 wireless barcode scanners. This is a perfect place to use wireless. A 5250 data stream has minimal bandwidth requirements, so you can have low speed and not notice a difference.

In our case, we use wireless on our production floor as well as in the warehouse. The production floor contains product testers that submit a 2K-byte XML file approximately once every 30 seconds. This is a good use of wireless as there are infrequent transmissions of a small file. With low bandwidth requirements, you can be assured that the wireless network will not become saturated and impede performance.

Users who consume large amounts of bandwidth are not good candidates for wireless. For example, applications like Microsoft Outlook can saturate a wireless network quickly as there is constant communication with a server to check for new email. Basically, if you're worried that 11 Mbps is not enough bandwidth, then I wouldn't recommend using any wireless standard currently available.

The Next Next Generation

In Europe and Japan, the European Telecommunications Standards Institute (ETSI) has developed its own 5 GHz standard called HiperLAN2. Using OFDM, it is similar to 802.11a. However, it provides better security and Quality of Service (QoS) features, while offering 54 Mbps of bandwidth. Products using this protocol are expected in the beginning of 2003.

However, due to the divide that this presents, a marriage of 802.11 and HiperLAN2 is imminent, and it will be entitled 5GHz Partnership Project (5-UP). With strong security, QoS features, and the ability to combine multiple channels into one large pipe, the 5-UP standard shows good signs of succeeding in the wireless industry.

Wrap Up

While wireless networking has been the only really profitable technology of late, it's now entering a stage where its future is uncertain. Both emerging standards offer benefits and speed increases, but neither is a clear-cut winner. Existing wireless users will look to 802.11g for backward-compatibility, and new users will look to 802.11a for better use of bandwidth. However, if you use it where it makes sense, then the speed upgrade shouldn't even be a concern!


Chris Green is a Senior Network Support Specialist located in Toronto, Ontario, Canada. He has seven years experience focusing on the iSeries 400 and networking technologies. Utilizing this experience, he has authored over 30 articles and several white papers and has co-authored an IBM Redbook entitled Securing Your AS/400 from Harm on the Internet. For questions or comments, you can email him at This email address is being protected from spambots. You need JavaScript enabled to view it..

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