Unweaving a wireless web of standards and applications
For a transmission method that has been on the books for a little more than five years, wireless local area networking (WLAN) certainly has its share of standard specifications...
For a transmission method that has been on the books for a little more than five years, wireless local area networking (WLAN) certainly has its share of standard specifications from the Institute of Electrical and Electronics Engineers (IEEE-www.ieee.org). In particular, the 802.11 family of standards specifies the transmission rates, frequency ranges, and other characteristics of the WLAN systems in place today.
The original 802.11 standard, ratified in 1997, specified a maximum 2-Mbit/sec transmission speed. Today's versions can move traffic significantly more rapidly. The 802.11 family of standards is popularly referred to as "WiFi." You can't go anywhere today, especially anywhere within the communications industry, without hearing and seeing the term WiFi. It comes from the words "wireless fidelity" and was conceived by a group called the WiFi Alliance (www.wi-fi.org) to validate certain 802.11-based wireless components that are interoperable with one another. Approved devices are allowed to use the WiFi mark. In the couple years since the WiFi Alliance initiated this campaign, the term "WiFi" has caught on, to say the least, and now is used almost ubiquitously to mean anything having to do with 802.11-based WLANs.
This basic diagram of a wireless network shows the practical uses of wireless connectivity in a commercial office building.
The three primary standards in the family are 802.11a, 802.11b, and 802.11g. Here is a synopsis of each:
802.11a uses the 5-GHz operating band and supports transmission rates up to 54 Mbits/sec.
802.11b uses the 2.4-GHz operating band and supports transmission rates up to 11 Mbits/sec.
802.11g uses the 2.4-GHz operating band and supports transmission rates up to 54 Mbits/sec.
Because 802.11b and g use the 2.4-GHz band, they are compatible with each other; neither is compatible with the 802.11a, 5-GHz specifications. As you might expect because of its lower-data-rate capability, 802.11b was the first of these three standards ratified. At the time it ratified the original 802.11 specifications, the IEEE could not assure users that all 802.11-compliant products would interoperate with one another. Hence the subsequent establishment of "wireless fidelity" testing and assurance.
WLAN transmission offers shared, not switched, transmission. A connection's throughput capacity is potentially reduced each time a user joins a service area. With that in mind, 802.11a is better equipped to handle high user traffic than 802.11b or g, because 802.11a uses up to 12 non-overlapping transmission channels, while 802.11b and g use three channels. The flipside of that fact is that 802.11a provides a 25- to 75-foot-radius operating range, compared to 802.11b and g's range, which goes as far as 150 feet. To effectively deploy the appropriate version of WLAN specifications, users must determine their own needs, including the amount and type of traffic that will be transmitted wirelessly, and the distances over which it must travel.
A number of other standards in the 802.11 series serve to enhance or otherwise supplement the three primary standards:
802.11d expands definitions found in the original 802.11 standard, effectively allowing the technology to be deployed in several countries.
802.11e provides quality of service (QoS) in a LAN environment, giving applications that are more time-sensitive (e.g., voice) priority over applications that are less time-sensitive (e.g., data). These specifications, still in draft, will be crucial for delay-sensitive applications such as voice-over-wireless-IP.
802.11f allows interoperability among wireless access points. Any 802.11f-compliant access point will interoperate with any other 802.11f-compliant access point.
802.11h is aimed at wireless users in Europe. It adds indoor and outdoor channel selection for 5-GHz license-exempt bands in Europe.
802.11i, approved in June 2004, it is a set of specifications that improves the security of WLAN transmissions over that of WEP-wireless equivalency protocol-itself an optional part of the original 802.11 specifications.
802.11k will provide methods for wireless network hardware to measure and report on radio resources, including interference and signal strength.
802.11n will create networks equivalent to the 100Base-T wired Ethernet network connection.
802.11v will define a wireless networking management protocol, allowing management of attached stations in a centralized or distributed fashion. The effort stems from the difficulties encountered trying to manage a WLAN via Simple Network Management Protocol (SNMP). Among the difficulties are that few wireless stations in the market include SNMP capabilities, using a secure SNMP protocol requires significant pre-use configuration of the station, and management of a station may be required prior to an IP connection. These facts prompt the need for a standardized approach to managing stations.
The 802.16 WiMax set of standards has been lauded by some as the best emerging technology in wireless transmission. Approximately two years ago, the IEEE approved 802.16a Air Interface for Fixed Broadband Wireless Access Systems. Commonly called WiMax, the standard set is intended to serve the metropolitan area network (MAN) market. Some contend it will be a competitor to Digital Subscriber Line as an access technology, but others claim (or fear) that it will compete with the 802.11 WiFi standard set in WLAN space.
The 802.16 standards that most affect corporate LAN users are:
802.16a, describing a fixed broadband wireless network designed with a theoretical range of 50 kilometers and a data rate up to 280 Mbits/sec;
802.16e, which describes a mobile broadband version of WiMax that will enable connections between moving access points.
Chipmaker Intel has been the most prominent supporter of WiMax technology, and has thrust it into the spotlight as a consideration for users considering implementing wireless connectivity. Debate rages in many circles about whether WiMax and WiFi are complementary (WiMax to the premises and WiFi within it) or competing (WiFi and WiMax competing for both on-premises and last-mile deployment).
At least one market analyst says the battle really doesn't exist. Phil Solis, senior analyst for wireless connectivity at ABI Research (www.abiresearch.com), points out that Intel expects to have chipsets ready for sale to laptop makers in mid-2006. Intel probably will be the first to market, he notes, followed by a couple other chipmakers. That means it will be several years before WiMax gains any real traction in the 802.16e market.
"We're not looking at WiMax even starting to compete against WiFi until 2007, when it will turn up in a few laptops," he says. "By then, WiFi penetration in laptops will be almost universal."
Before WiMax chipsets appear in computers, customer premises equipment receivers will be able to get signals from local transmitters, Solis and ABI further state. But that still leaves the rest of the devices in a corporate or home network unconnected. And putting WiMax chips, which will have high power consumption, in handheld wireless devices such as personal digital assistants and mobile phones will be more difficult than putting them in laptops. Alas, Solis predicts, the combined scenario of WiMax to the building and WiFi for the interior network should satisfy users.
Other wireless specifications
In addition to the WiFi and WiMax standards, other specifications also define the characteristics of wireless transmission, inside and outside of LANs:
802.20 will describe a mobile broadband wireless access system that will support mobility for vehicles moving up to 155 miles per hour with a 15-kilometer range, at transmission rates of 1 Mbit/sec or greater.
802.15.3a will detail an ultrawideband, short-range, high-speed system using a range of frequencies, which could be used to replace cables in home entertainment and computing products.
Bluetooth 1.2, adopted in late 2004, is an improvement over the original Bluetooth specifications, adding adaptive frequency-hopping to reduce interference, improve voice quality, and speed-linking between devices. Bluetooth uses the 2.4-GHz band, which is also used by 802.11b and g as well as common devices such as cordless telephones and microwave ovens. The enhanced frequency-hopping features in Bluetooth 1.2 allow the protocol to transmit at available frequencies within the spectrum, essentially avoiding interfering with other wireless devices in the same frequency range.
Contractors and system users entering the wireless arena for the first time easily can be dismayed at the number and types of technologies available. Having a grip on the standards that govern this type of transmission is a necessary first step to deploying them at maximum efficiency.