A marriage from hell

The tendency for mobile devices to stay faithful to the first access point they connect to is leaving users with weak signals and awful throughput rates.



commentary The tendency for mobile devices to stay faithful to the first access point they connect to is leaving users with weak signals and awful throughput rates.

I've looked at WLAN before in this column but have been a little short sighted when assessing the abilities of current WLAN technology to meet the world's mobile population. In particular, what it means to be truly mobile.

We recently carried out some testing that opened our eyes to fundamental problems with the current 802.11a/b/g wireless implementations.
It's a pretty simple mistake to make because most of us interpret the word as meaning to move from one place to another and each time we stop do some wireless computing. Usually many wireless infrastructures only have to deal with a user who wanders over to some convenient desktop, fires up their notebook, connects to the nearest and strongest wireless access point (AP), authenticates, and then proceeds to work away. They may then need to move to a different site to carry out another facet of their work but the important point is that while travelling to the other site the notebook is powered down and certainly not in use. Once at the new location the "connect and authenticate" scenario is repeated.

We recently carried out some testing for a client that opened our eyes to fundamental problems with the current 802.11a/b/g wireless implementations and most of them involve true mobility.

During our testing we found there are two significant stumbling blocks to mobile computing which I define as the ability to wander around with a portable wireless device and remain effectively and efficiently connected at all times. Unfortunately, if your wireless infrastructure adheres rigidly to the current standards this will just not occur.

Under the current standards, when your mobile device associates with an AP it's almost like the marriage vow "until death do us part". As you travel further from the AP the software in your mobile device clings like grim death to the AP. Even if you travel within a couple of metres of an AP with a much stronger signal your mobile device and original AP connection will still prevail.

In effect, the mobile device will only start searching for a new AP when the signal is so weak that it can no longer reliably pick up beacons from the initial AP. This means many mobile devices are persisting with a weak AP signal and pretty horrible data throughput rates. Now as romantic as this "marriage" to the original AP may sound, it isn't the most effective use of available AP resources.

Take this likely scenario: It's stocktake at a large retailer's distribution centre, the staff are using mobile devices to go from product to product scanning barcodes and inputting stock numbers on the keypads. The data is fed back to a database via the distribution centre's WLAN infrastructure. But here is the kicker: most of the devices are picked up from a single location where they sit in charging stations ready for use. As each user wanders in and powers up a mobile device they all associate with the closest AP. Now, the current standards don't cater for load balancing so we have a single AP trying to provide bandwidth to multiple devices while the other APs remain unused until users move far enough away to force an association with those other APs.

802.11e is supposed to address many of the current quality-of-service problems with WLAN for time-sensitive applications such as video and voice over IP but may not address some of the other problems I've been talking about. In the meantime, some vendors such as Cisco and Symbol have struck out on their own to address the issues of intelligent "pre-emptive" roaming and load balancing.

Unfortunately, if you need true wireless mobility, you are stuck with the proprietary solutions of a handful of vendors. Until the arrival of effective mobility standards there is no other choice.

Steve Turvey is Lab Manager of the RMIT IT Test Labs. Send feedback to tandb@zdnet.com.au.

This article was first published in Technology & Business magazine.
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