Wider Range of Rates

By Andrew Garcia  |  Posted 2008-04-14 Print this article Print


Wider Range of Rates

The available data rates offered by 802.11n networks, which now extend all the way up to 300M bps (or up to 600M bps in future 4-by-4 antenna implementations), are determined by several factors: the number of simultaneous streams, the width of the WLAN channel and the length of the guard interval (a waiting period built into the standard to avoid echo effects, which has been shortened for 802.11n).

802.11n analysis tools will need to identify not only the data rates advertised for an 802.11n WLAN but also the reasons why those particular rates are available, in order to help administrators identify possible mis-configurations in the new standard's wide variety of tunable knobs.


Beamforming-an optional feature of 802.11n under which APs dynamically switch antenna combinations to focus wireless transmissions on a particular wireless client to maximize reception for that station-will also cause headaches for wireless administrators.

Current models for overlay networks fail to provide accurate coverage information in a network using beamforming.

A stationary WLAN sensor will struggle to accurately predict client coverage in this sort of network because the AP's antennae are not pointing at the sensor. Combating this problem will be tough, as vendors will need to include either client-side analysis (requiring some kind of agent on all WLAN
clients) or denser wireless sensor deployments. The latter scenario seems untenable because 802.11n is often billed as a way to lessen the number of sensors deployed in an enterprise due to the technology's improved performance at longer distances.

Frame Aggregation

Normal WLAN activity includes a lot of management frames, and this is why throughput totals reported in tests are significantly less than the advertised data rate. 802.11n introduces two flavors of frame aggregation-8KB MAC Service Data Unit Aggregation and the 65KB MAC Protocol Data Unit Aggregation-both of which allow for more data to be sent over the air with less management overhead.

802.11n-enabled analysis tools should be able to clearly identify when frame aggregation is in use and which type is being employed-as each type has different rules surrounding re-transmits if the packets are damaged. ??

eWEEK Labs Senior Analyst Andrew Garcia can be reached at agarcia@eweek.com.


Andrew cut his teeth as a systems administrator at the University of California, learning the ins and outs of server migration, Windows desktop management, Unix and Novell administration. After a tour of duty as a team leader for PC Magazine's Labs, Andrew turned to system integration - providing network, server, and desktop consulting services for small businesses throughout the Bay Area. With eWEEK Labs since 2003, Andrew concentrates on wireless networking technologies while moonlighting with Microsoft Windows, mobile devices and management, and unified communications. He produces product reviews, technology analysis and opinion pieces for eWEEK.com, eWEEK magazine, and the Labs' Release Notes blog. Follow Andrew on Twitter at andrewrgarcia, or reach him by email at agarcia@eweek.com.

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