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Wireless Metropolitan Area Networks
WMANs are fixed broadband wireless access links that connect entire subscriber networks to a base station at a wireless carrier's point-of-presence (POP). For example, a WMAN might link an office building to a Wireless ISP (WISP) in the same city, using wireless as a "last mile" alternative to save the cost of installing a T1 or DSL link. WMANs are capable of carrying tens of megabits per second up to 31 miles. Common WMAN technologies include:
|802.16 (WMAN-SC)||10-66 GHz||10-30 miles||134 Mbps||Fixed, line of sight, point-to-multipoint "last mile" links between subscribers and public carrier base stations|
|802.16a (WMAN-SCa)||2-11 GHz||31 miles||70 Mbps||Last mile links where line of sight is not available, may use licensed (e.g., 2.5-2.7) or unlicensed (e.g., 5.725-5.825) spectrum|
Fixed Broadband Wireless Access (FBWA) technologies like LMDS and the original 802.16 standard have been around for several years, used exclusively by public carriers who purchase licensed spectrum to operate WMAN services. The 802.16a amendment, published in 2003 and known as WiMAX, overcomes earlier WMAN limitations. Specifically, higher frequency 802.16 requires line-of-sight between the subscriber location and the carrier's base station. Lower frequency 802.16a no longer requires line-of-site, which means that it can be used in urban and rural environments where buildings, trees, and mountains would inhibit older services.
What's more, 802.16a can operate at several discrete frequencies within the 2-11 GHz range, including both licensed and unlicensed bands. Unlicensed spectrum means that WiMAX is not just for public carriers anymore. WISPs now using 802.11 for low-speed, multi-hop backhaul links will be able to use 802.16a to create higher-speed links that span longer distances. WiMAX is much better positioned to carry larger volumes of traffic generated by several subscriber networks to POPs that are 10, 20, even 30 miles away. Products supporting 802.16a are expected to become widely available in the second half of 2004.
Wireless Wide Area Networks
WWANs are what we all used to think of as cellular phone technologies. WWANs are designed to provide near-continuous coverage for subscriber handsets that roam across a public carrier's serving area. Serving areas are composed of many smaller cells, joined together into nationwide networks that span entire cities and geographic regions.
Older second generation (2G) WWAN technologies are digital voice networks that have been retrofitted and extended to carry data and "personal communication services." Newer third generation (3G) WWANs have been explicitly designed to support higher-speed data and streaming audio/video applications. Today, over a dozen WWAN technologies have been defined, including:
|Global System for Mobile Communications (GSM)||900, 1800, 1900 MHz||Depends on carrier, international||9.6 Kbps||Digital voice, short message services, short data transactions between field terminals and back-office servers|
|General Packet Radio Services (GPRS)||900, 1800, 1900 MHz||Depends on carrier, international||171 Kbps (40 Kbps typical now)||Voice, messaging, email, and wireless web on Blackberries and other phones/pagers/PDAs from AT&T, Cingular, T-Mobile, etc.|
|Code Division Multiple Access (CDMA)||800, 900, 1700, 1800, 1900 MHz||Depends on carrier, US||14.4 Kbps||Digital voice, short message services, PCS, wireless web on WAP Phones|
|CDMA2000/1X||450, 800, 1700, 1900, 2100 MHz||Depends on carrier, international||307 Kbps (40 Kbps typical now)||Voice, messaging, email, and wireless web on Smartphones and other phones/pagers/PDAs from Sprint, Verizon, etc.|
All of these services operate in licensed spectrum. There are two main evolutionary branches in this tree: GSM and CDMA. GPRS is a 3G extension to worldwide GSM standard. CDMA2000 is a 3G replacement for the less widely used CDMA. Today's 3G network speeds fall far short of their theoretical upper limits, but are often comparable to using v.90 dial-up over a landline. Both branches are expected to grow into faster multi-megabit service offerings, like GPRS EDGE and CDMA2000 1xEV-DV.
Today's 3G WWAN services are commonly found in Blackberries, Smartphones, and some PalmOS PDAs. WWANs are also supported by Compact Flash and PC Card modems for PDAs and laptops, but these are not yet widely used. Handset manufacturers are working on dual-mode WWAN + WLAN devices that would be capable of using voice-over-IP on wireless LAN hot spots where available, switching to wireless WAN services elsewhere. WLANs are often faster and cheaper, but WWANs are far more ubiquitous. That makes a device that can use either interchangeably sound attractive, but there's a lot yet to be done before that vision can be fully realized.
By breaking wireless technologies into categories based on application and distance, it becomes easier to understand the fundamental differences between wireless PANs, LANs, MANs, and WANs. Just picture these four categories as rings that get incrementally bigger, and think about the reach that your own wireless application requires. Within each category, technologies can be harder to differentiate, so follow the links embedded in this tip to learn more.
About the author: Lisa Phifer is vice president of Core Competence, Inc., a consulting firm specializing in network security and management technology. She is also a site expert to SearchMobileComputing.com and SearchNetworking.com.
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