SmallNetBuilder

Introduction

Quite some time ago, a reader wrote to complain that he had to constantly power-cycle his access point because it kept locking up on him. He also posed the question: "If I spend more, do I get a more reliable product?".

I thought that was a very good question, but didn't really have a good way to answer it at the time. Although single-client throughput testing is fine for seeing how fast WLAN gear can go, a single wireless link really isn't sufficient to make current-generation AP's break a sweat.

Fortunately, time and the march of technology have provided a solution to simplifying WLAN load-testing in the form of Communication Machinery Corporation's Emulation Engine (since acquired by Ixia). Armed with this handy little box, I set out to separate the 98 pound weaklings from the kings of the wireless beach. What I found, however, may surprise you...

CMC's Emulation Engine

Think of the Emulation Engine (EE) as an access point in reverse. Instead of providing connection to a wired LAN for multiple wireless clients or stations (STAs), it generates multiple wireless STAs that can transmit and receive data to / from a target wireless AP or router. The data sent can be either simple internally-generated ping traffic, or come from an external traffic generator such as Ixia's IxChariot.

Figure 1: CMC's Emulation Engine

These multiple STAs aren't the product of a bunch of radios crammed into the EE's enclosure, but are instead virtual stations (vSTAs), all generated from a single mini-PCI radio. Each vSTA has its own IP and MAC address and individually authenticates, associates and transmits and receives data.

CMC produces a number of Emulation Engine models and recently upgraded its product line to its more powerful XT platform. They also introduced a model capable of exercising APs using data secured by Wi-Fi Protected Access (WPA). But I agreed to use a previous-generation EE a/b/g model, since its ability to test 802.11a,b and g APs with WEP enabled was fine for my purposes, and CMC was able to loan it to me for longer than any of the newer platforms.

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