Making wireless work

By: David Connors
Date: 13 July 2009 | Category: tech•ed 2009, wireless | Tags: cisco,gccec,HP mini-note,wireless

If you’re interested in tech•ed and have been reading the blogosphere you’ll know that every paying delegate is scoring an awesome HP Mini 2140 as a freebie! This is fantastic news for delegates and a real headache for the propeller heads behind tech•ed. We now know that we’re going to have 2500 laptops, plus delegate’s bringing their own laptops, plus wifi-enabled mobile phones, plus Microsoft staff, speakers, crew, and all of the leechers holiday-makers in Gold Coast apartments across the road to cater for as wireless users.

In past tech•eds we have designed a wireless network specifically for each venue using a few tricks to given excellent throughput. Firstly, we normally use a very low powered 802.11b-only network to service legacy devices only. We then overlay a completely separate 802.11g-only network (excluding all data rates below 18mbps – more on why in a future post) at whatever power level we determine will give the best coverage for the most users. We use a series of panel antennas to control and minimise the inevitable channel overlap. The net result of this design work is that we can deliver post commissioning data rates of 2500 kilobytes per second from the Internet (which is the about as good as you’ll ever see out of an 802.11g network). We normally use approximately 20 Cisco Aironet 1232 access points with a and/or bg radios installed.

This has worked really well for Microsoft in the past as we have only ever really officially offered wireless in select common foyer areas and the exhibition hall areas. This year, however, things have been ratcheted up a whole number of notches due to the giveaway of the HP Mini 2140 devices.

Wireless hardware for tech•ed 2009

GCCEC has recently installed a new Cisco 4404 Wireless LAN Controller with 50 x Aironet 1252 lightweight access points with abgn radios installed throughout the entire complex.

This differs greatly from most wireless network scenarios you’re probably used to in that:

• The Wireless LAN Controller is a centralised management device that manages all of the access points.
• All of the access points are ‘dumb’ in that they receive firmware and configuration information directly from the controller.
• All traffic from the individual access points is delivered to the Controller over copper Ethernet and then distributed to the local area network by the Controller using 2 x gigabit fibre uplinks.

There are a few key benefits in this architecture, the primary being that there is a single device (the Controller) with a complete understanding of all access points on the network. This means that:

• The Controller can manage the channel selection and power selection settings across the network. The Controller will therefore (allegedly) ensure that near-by access points are not assigned to conflicting channels.
• The Controller works proactively to understand and close coverage gaps in the network.
• The Controller understands where all the walls are, roughly what they’re made out of (so it understands the db loss caused by the wall), ceiling heights and so on.
• In some scenarios the Controller can detect if clients at the edge of the network are having trouble connecting and so crank up the power levels accordingly.

“Wow! That sounds amazing … 50 APs will handle anything!” I wish that were true however as you’ll learn in coming posts, there is no such thing as a free lunch (well there is if you work as crew at the event but you don’t want to see what we get fed out back).

There are a number of issues with the WLAN deployment at GCCEC that we have to resolve before the event. This series of articles will keep you updated on how we’re doing with root cause analysis and implementing the necessary fixes.

Coming up next:

• Diagnosing and resolving extremely high RF utilisation
• Diagnosing and resolving intermittent throughput problems on individual radio interfaces (Scheduled to be onsite to crack this one on Thursday … write up will follow that)