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Where’s The Wi In WiMax?

By Tony Rybczynski & Cherif Sleiman

 

If you are like many in the industry, you’re probably confused about WiMax (Worldwide Interoperability for Microwave Access). You know that 802.11 WLAN standards are focused on Ethernet and handle Ethernet frames up to 1,500 bytes. WiMax, on the other hand, or IEEE802.16 as it is formally known, is designed to seamlessly carry any higher layer protocol, such as ATM, frame relay, Ethernet, or IP, and supports frame concatenation and is fundamentally a higher power longer range technology. So what’s the relationship between WiMax and WiFi? Will WiMax replace WiFi?

WiMax In Your Neighborhood
The 802.16 spec is full of optionality, only a subset of which is needed for typical deployments directed at specific markets. Adaptive burst profiles are used to increase the system capacity. The frame structure allows terminals to be dynamically assigned uplink and downlink burst profiles to allow trade-offs between capacity and robustness in real-time. In contrast, 802.11 is very much focused on one general environment: wireless LANs, whether in buildings or hotspots, or more recently across campuses through wireless mesh networking. Consequently, a WiFi-enabled device cannot talk to a WiMax base station; one is not a subset of the other.

WiMax provides a range of mechanisms targeting bandwidth efficiency. For example, multiple user frames can be concatenated into a single burst to reduce bandwidth overhead. In contrast, IEEE802.11 follows the KISS principle and addresses bandwidth capacity through new development such as 802.11n, which targets full 100Mbps bandwidth to the mobile user.

WiMax operates in various licensed and unlicensed bands between 2 and 66 GHz, including the unlicensed bands of 2.4 and 5GHz used by WiFi. This highlights a third major difference. The full potential of WiMax over tens of miles with aggregate bandwidth of 70Mbps (or 1 Mbps per user) is only achievable at the higher power levels supported in the licensed bands, often requiring line of sight. Licensed operation is only available to service providers and specific operators (e.g., public safety agencies). Operating in the unlicensed bands limits the applications of WiMax to a three-to-five mile radius, initially for fixed applications. WiFi coverage is typically for cells of 100 meter radius.

IEEE 802.16 is initially targeted at fixed broadband wireless access systems employing a point-to-multipoint architecture, and seamlessly carrying protocols such as frame relay, ATM, Ethernet, or IP. The largest application is as an alternative to DSL and cable modems for public network access for consumers and small business users. It is not initially for mobile users, though it can be used as an alternative to wired solutions between buildings. Therefore, WiMax and WiFi are different technologies targeting different markets.

WiMax WiFi Convergence
WiMax and WiFi are converging in three ways: network convergence, voice convergence, mobility convergence.
Network convergence brings WiFi and WiMax technologies together to expand geographic scalability. In an environment in which wired Ethernet to each Access Point (AP) is cost prohibitive (e.g., across a campus or shipping yard), WiMax can be used to wirelessly backhaul APs to a central wired base station. This is an alternative to Wireless Mesh Networks, whereby WiFi APs dynamically learn about each other and wirelessly route packets reliably across this mesh. WiMax provides better reach, but mesh solutions typically have lower operational costs (via plug-and-play) and higher reliability (via dynamic routing).

Voice convergence expands the application fit of wireless solutions through QoS. WiFi is doing this through a new standard called 802.11e. WiMax has developed a number of WiMax specific mechanisms for QoS. This includes frame fragmentation, a self-correcting bandwidth request/grant scheme that eliminates the overhead and delay of acknowledgements, and polling mechanisms. IP telephony can therefore run over both WiFi and WiMax networks.

Mobility convergence is inherent in WiFi across APs in a single IP subnet, has been extended to enterprise-wide roaming, and is being extended to seamless roaming for voice and data between enterprise and public 2G/3G cellular networks. WiMax is moving from fixed broadband access to mobility through an extension called 802.16e (with initial rollouts in 2006). While mobility in a WiFi environment supports mobility at ambulatory speeds, in a WiMax environment, it is intended to support speeds that are an order of magnitude greater. Once developed and mature, these could compete against 3G wireless solutions. We can foresee multimode mobile devices that support WiFi, WiMax, and 3G wireless roaming.

So where’s the Fi in WiMax? WiMax is not a replacement for WiFi, nor is it interoperable with WiFi. In fact it’s more complementary to WiFi by providing reach and more competitive with third-generation public cellular technologies by providing wireless bandwidth over long distances. But these two technologies are converging with respect to network solutions that integrate both, with respect to supporting voice and with respect to mobility, including convergence in mobile devices.

What WiMax now needs is acceptance by a major economic power. GSM was propelled by Europe, CDMA by the U.S. and Korea. But what would happen if the emerging giants of India or China adopted it as their standard? IT

Tony Rybczynski is the director of strategic enterprise technologies for Nortel. He has over 30 years experience in the application of packet network technology. Cherif Sleiman is technology strategy leader for Nortel’s Enterprise business unit, responsible for technology roadmaps associated with multimedia networks. For more information, please visit the company online at www.nortel.com.

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