Wi-Fi: Productivity Found but Choices Loom

Lots of Standards

Intel recently announced a gain of about two hours of extra productivity per week from its workforce by moving them from desktop PCs to mobile laptops and notebook computers. Add wireless connectivity and you’ve created a work environment that is responsive and serves customers better.

While the benefits of wireless networking and mobile computing are obvious, how to get there isn’t and can become a confusing as you navigate the various standards for Wi-Fi networking that are available. Wi-Fi networking is hardly new, the first wireless LAN (WLAN) standard (designated 802.11 by the IEEE) was ratified in 1997 for data rates up to 2Mbps in the 2.4GHz unlicensed band. As usage of the technology grew, the IEEE ratified two additional amendments to the 802.11 physical layer standard in 1999 to address the speed and capacity limitations inherent in the first standard.

The first amendment to the IEEE standard was 802.11b which provided for data rates up to 11Mbps within the 2.4GHz band. Concurrently, 802.11a, added support for data rates up to 54Mbps within the 5GHz.

To add to the growing list of standards, the industry ratified another IEEE standard in 2001 dubbed 802.11g providing data rates up to 54Mbps but in the same frequency band (2.4GHz) as 802.11b making it backwards compatible to the original 802.11b standard.

Advances in Clients – Cheaper devices, more functionality

Over the past 2 years, the cost of Wi-Fi chipsets has significantly come down leaving little difference between the cost of products operating in the 2.4GHz and 5GHz bands. The result of this cost erosion is that most new 802.11 client adapters and access point products now offer all three modes of operation in a single device allowing a user to connect to any available 802.11a, 802.11b, or 802.11g network.

In addition to the influx of “traditional” Wi-Fi computing clients such as laptop computers, the number of application specific devices such as Wi-Fi enabled cellular phones will dramatically increase over the next year ending up on the IT administrator’s doorstep. These hybrid cellular phones will be able to carry voice traffic over the Wi-Fi network and will quadruple the number of devices needing access to your network.

This explosion in client connectivity, along with the time-sensitive nature of voice traffic will force capacity, the need for more channels and cleaner spectrum to the forefront of deployment issues to resolve within the enterprise which if not correctly dealt with – will minimize the performance of the wireless network and productivity gains that are expected.

The Hidden Issues of a Wi-Fi Deployment

802.11b and 802.11g products have only three non-overlapping channels (1, 6, 11) to use compared to 802.11a which currently has twelve non-overlapping channels defined and has been allocated an additional set of channels for use in the U.S. by the FCC which will take the number to 23. The bottom line; the more non-overlapping channels, the more bandwidth (capacity) is available to the user.

Over the past three years, most enterprise WLAN deployments were based on the 802.11b standard and those deployments were architected to provide the maximum amount of coverage with the fewest number of access points. Maximizing coverage was the key driving factor in these deployments because only a small number of users were active and there was a desire to deploy a limited number of access points due to cost and management considerations.

As more and more Wi-Fi clients started accessing the network, IT administrators would add additional access points to handle the needed increase in bandwidth (capacity). However, additional access points create an issue of channel interference given the limited number of non-overlapping channels that exist
within the 802.11b/g standard.

Deploying 802.11a provides far less channel reuse and avoids inter-cell interference and allows high data rate transmissions within each cell providing maximum capacity. The optimal WLAN deployment makes the maximum number of non-overlapping channels available in both 802.11b/g and 802.11a standards while deploying the fewest number of access points in a given coverage area. This provides for the greatest amount of aggregate network capacity for Wi-Fi clients plus supporting legacy devices. This is especially critical for applications such as voice over Wi-Fi (VoWLAN) that drive a substantial number of clients in a given area.

802.11n: The Future of Wi-Fi

While many in the industry are touting 802.11n as a path to higher performing (bandwidth) Wi-Fi networks, there are a number of important items to consider when making your deployment decisions today! In reviewing the technical underpinnings of 802.11n, fully half of the improvement that 802.11n provides comes from the ability to combine two adjacent RF channels to double the throughput of a link. Unfortunately, only 3 non-overlapping channels exist in the 2.4GHz band meaning at most; only two channels can be “bonded” together to increase throughput. The remaining non-overlapping channel can be used at half the throughput of the bonded pair. Contrast this with the available non-overlapping channels in the 5GHz band of 802.11a which has up to 22 non-overlapping channels. This provides up to 11 pairs of bonded channels that will be available for 802.11n devices in the 5GHz band.

Another important consideration is legacy devices that are already occupying a channel in the 2.4GHz band will prevent bonding altogether, or greatly reduce its performance. This can already be seen today where 802.11b devices are prevalent. In the 2.4GHz band, 802.11g clients are drastically slowed down by 802.11b clients– the same will be true for 802.11n as 802.11b clients will drastically reduce the throughput of 802.11n devices in the 2.4GHz band. In contrast, 802.11a clients will be much better partners for 802.11n devices, as they will interoperate at five times greater data rates, which will increase the overall performance of the network. Because only a single channel can be bonded for 802.11n in the 2.4GHz band, existing 802.11b devices will drastically reduce overall
throughput.

To obtain the benefit promised by 802.11n, the best action to be taken by IT administrators NOW is to ensure the purchase of Multi-mode 802.11a/b/g client adapters and infrastructure equipment to allow the best compatibility with legacy devices, and will allow the best performance with future 802.11n networks in the 5GHz band.

Get the Most from Wi-Fi

To get the most performance from your Wi-Fi network ensuring your employees operate at peek efficiency, standardize on Wi-Fi equipment that supports 802.11a/b/g standards and can use all the non-overlapping channels simultaneously. This approach limits interference and maximizes the RF bandwidth available within a given coverage area.

To learn more about Xirrus and how our products can deliver the highest performing Wi-Fi networks, download our White Paper on Wi-Fi Sectorization at www.xirrus.com/whitepaper