• United States
Neal Weinberg
Contributing writer, Foundry

Trapeze WLAN switch

Nov 04, 20033 mins

* The Reviewmeister finishes up his WLAN tour with products from Trapeze and Symbol

The Reviewmeister looked at the Airespace and Aruba wireless LAN switches last week, and this week we finish up our WLAN tour with products from Trapeze and Symbol.

All WLAN vendors agree that provisioning is critical. Because the radio frequency spectrum is finite, allocating bandwidth is trickier than in the wired world.

When a conventional Ethernet segment is saturated, the easy fix is to allocate more bandwidth, by increasing the port count or port speed. In the wireless world, you can’t do that, as access points can interfere with one another or be placed in “dead spots” with no coverage. 

Some means of managing a WLAN rollout is needed. Trapeze has an automated site survey tool called RingMaster. With RingMaster, you supply the number of users or workgroups and the bandwidth requirements for each, and then input CADs of floor plans. RingMaster combines these inputs with building factors and signal loss formulas. The result is a work order showing contractors exactly where each access point should be placed.

In this test, we’ve conducted the first public measurements of WLAN delay. Past performance tests focused only on forwarding rates, even though delay can have a far more significant effect on application performance.

Also, we ran tests involving multiple access points, not just the single-access-point tests that are commonly used (even in Wi-Fi certification). After all, a key goal of WLAN switching is to extend the number of WLAN attachment points.

We used NetWarrior, a traffic generator/analyzer from QoSmetrix, and custom-developed test routines for this project. QoSmetrix supplied four NetWarrior units, with one acting as a generator on the wired Ethernet side and three acting as clients on the WLAN side. All NetWarriors use Global Positioning System receivers for time synchronization within 40 nanoseconds.

With the locations of the NetWarriors fixed, we asked WLAN switch vendors to place their access points anywhere within our lab. Our choice of three access points was deliberate: In theory, three different 802.11b access points should be able to coexist in the same space without interference by using three different channels.

No system tripled forwarding rates in tests with three or four access points, even though three access points theoretically should not interfere with one another.  Trapeze did score an impressive 91% of the total possible forwarding rate.

And no system came anywhere close to delivering the 11M bit/sec nominal rate of the 802.11b standard. The huge amount of 802.11 management and control traffic, plus contention for the radio frequency spectrum, makes up the overhead.

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