Mapping your wireless local area network: How to make your WLAN shine
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The growth of wireless devices has placed increasing demands on networks initially designed for limited guest access. And even as the hype-engine for 4G/LTE ramps up, the reality is that even reliable 3G coverage in most countries is still distinctly lacking. As a result, many businesses are forced to concoct wireless networks that envelope a motley crew of personal devices.
Increasing the capacity and functionality of your corporate network isn't necessarily an easy sell. Once the RFPs come back from your service provider, one or maybe more of the following is usually heard echoing around the corridors of most boardrooms: "How much?" A thud as bodies falls from chairs. "My home wireless only costs $100!"
Now, the first two responses I can't help address, but I can explain the price differential between enterprise solutions and that little router than came free with your home broadband package.
Security, scalability and performance are critical
The wireless technology built into consumer electronics is not a single piece of software or hardware, but rather a large number of protocols, local regulatory restrictions and proprietary customizations. In a typical home access point (AP) capable of supporting a few wireless users, a great deal of complexity is hidden. This is possible because the requirements for a home user are very narrow and straightforward. Security, scalability and performance are not especially critical so assumptions are made to produce a "good enough" solution for home users.
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Connecting WLANs most efficiently
In a corporate environment, many of these assumptions just simply won't scale. For wireless to work over any great area, multiple APs must be deployed. For users to be able to roam, APs must work in concert to ensure that connectivity is maintained as (for example) a user moves around a building. Furthermore, confidentiality and security are much greater concerns in an enterprise environment. The greatest issue is availability. It might be inconvenient if your neighbor next door happens to be using the same wireless frequency as you do, thus forcing your Web browsing to slow. In an enterprise, mission-critical environment, any slowdown is unacceptable.
Without delving into significant technical detail, modern wireless technology is described in the Institute of Electronics and Electronics Engineers' 802.11 suite of protocols. These standards, and there are dozens of them, all interact to enable wireless service. Here are some of the key fundamentals.
All wireless communication requires access to a finite wireless spectrum. For example, modern Global System for Mobile (GSM) cellular mobile phones use the 900 MHz and 1800 MHz bands while in the United States, police and weather radar use 8.5 GHz to 10.55 GHz. Access to virtually all frequencies is regulated and controlled; licenses need to be acquired before a device can operate in any given band. Certain frequencies are available for general use by low-power devices.
The two public-access spectrum bands in common use are 2.4 GHz and 5 GHz. These two bands are used by Wi-Fi compatible networks. There are other spectrum bands available, but these are very narrow indeed and have very specific use cases (such as digital enhanced cordless phones on 1880 MHz–1900 MHz). Some key 802.11 standards describe the usage of the 2.4 GHz and 5 GHz bands in the context of wireless networks. They are:
- 802.11a -- Describes the use of the 5 GHz band; this band provides a maximum of 54 Mbps of throughput in 20 or more non-overlapping channels, up to a maximum distance of approximately 50 feet. (A non-overlapping channel can be considered a 20 MHz-wide channel over which a device can transmit without the signal leaking into an adjacent channel. Think of non-overlapping channels as being akin to Ethernet switch ports; the 2.4 GHz band has three "ports" while in the United States, the 5 GHz band has 20 ports -- with up to 23 in some countries.)
- 802.11b -- Is the legacy standard (but still relatively common) that describes the use of the 2.4 GHz band to provide up to 11 Mbps of bandwidth, up to approximately 150 feet.
- 802.11g -- Also covers devices operating in the 2.4 GHz band to provide up to 54 Mbps of bandwidth up to approximately 150 feet, with three non-overlapping channels. Because 802.11b and 802.11g share the same spectrum, any "b" devices operating in the same area will reduce the bandwidth available to "g" devices on the same channel, wasting existing spectrum.
- 802.11n -- Describes recent amendments to the 802.11 protocol, which allows the "multiplexing" of the available channels in either the 2.4 GHz or 5 GHz bands to produce significantly improved throughput up to 600 Mbps over longer distances. This is achieved by using up to four wireless radios and antennae on access points and clients in a "MiMo" (multiple-in, multiple-out) configuration.
- 802.11ac -- Provides gigabit speeds on the 5 GHz band. Only a handful of vendors are currently shipping ac-capable devices. This nascent technology is not yet widely deployed and, for now, a stable 802.11n network will be a more pragmatic approach than a bleeding-edge 802.11ac framework.
If nothing else, it's worth remembering these six points:
- The available wireless spectrum is finite and limited by regulation.
- Wireless networks cannot match the performance or capacity of wired networks. As Mathew S. Gast wrote in 802.11 Wireless Networks: The Definitive Guide, 2nd edition, in 2005, "For the benefit of mobility, wireless networks impose a cost. Simply, performance is nowhere near what can be expected from a well-engineered wired LAN."
- The presence of legacy 802.11b devices connecting to the network will dramatically reduce the available bandwidth for 802.11g and 802.11n devices.
- The 5 GHz band has more available bandwidth than the 2.4 GHz band, but it is effective over a shorter distance.
- Many devices will "prefer" the more congested 2.4 GHz band even if they are capable of connecting to an access point on the 5 GHz band.
- The maximum available continuous throughput is dependent on many factors including distance and interference, and does not take into account protocol overhead, which may be as much as 45%.
Much like Ethernet switched networks, there is a lot of stuff happening behind the scenes in wireless networks in order to make them work well. Perhaps this primer will give you the information you need to lessen the sticker shock from your next wireless network RFQ.
Glen Kemp is an enterprise solutions architect for a UK-based managed services provider. He designs and deploys network and application security tools, including access control, remote access, firewalls and other "keep the bad guys out" technologies. He is an experienced professional services consultant; delivering elephants and not hunting unicorns. He is also a guest blogger for the Packet Pushers Podcast and a Juniper Ambassador. Follow him on Twitter @ssl_boy.