With one of the largest campuses in the UK, rolling out a quarter-of-a-million-pound wireless network at the University of Birmingham was always going to be a big challenge.
The university's IT department is covering every inch of the 250-hectare campus with a Wi-Fi network — inside buildings and out — to give its 36,000 students and staff access to information wherever they are. The project is due for completion by the end of the year and is set to deliver one of the country's largest wireless networks.
Upgrading the network
The network upgrade was the brainchild of John Turnbull, the university's head of networks, and Chris Lea, a senior network specialist at the institution. Faced with an ageing LAN infrastructure in 2002, Turnbull knew a major upgrade was essential to meet the demands of students used to wireless connectivity.
The existing LAN was not up to scratch, said Turnbull. It was based on four switches from 3Com — a vendor which backed out of the networking market, leaving behind many unhappy customers — arranged in an FDDI ring, trundling along at 100Mbps. Eight fibre links were required between each switch, consuming a hefty portion of the IT budget.
Two related initiatives were required to turn around the ailing network. At the beginning of the project in 2002, Turnbull upgraded the existing switches to allow them to accommodate 10Gbps blades. The increased bandwidth meant only one fibre link was required between each switch, which freed up 35 fibre pairs and 80 GBICs (gigabit interface converters) with a cost saving of £87,000.
The upgrade enabled the second initiative to take place: the now spare fibre could be used to form the backbone of a new network containing the Wi-Fi access points. Rolling out Wi-Fi would offer multiple advantages. Not only would it give students access to their network resources right across the campus, it would provide a backup network if ever the fixed LAN went down.
The fact that the Wi-Fi access points were on a separate network to the wireline LAN would also have a further advantage: raising the level of security. "I wasn't convinced of security at the access point," said Turnbull. "I was concerned about students coming in with laptops [harbouring] viruses and worms. We have a site firewall and building firewalls where there is sensitive data, but we would have been letting them on behind that firewall and the viruses could have spread to the rest of the network."
To mitigate that risk, Turnbull designed the Wi-Fi network to run in parallel with the fixed network, connecting at only two points through a firewall. In that way, if a virus were let loose on the wireless network, it couldn't affect anything on the fixed network. The wireless network could then be disconnected while the situation was resolved.
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The division of the fixed and wireless networks also came in useful in another, unexpected way. The IT department was asked to intervene to help a senior visitor to the arts faculty who complained of suffering from electrosensitivity to Wi-Fi. The team was able to cut the Power-over-Ethernet supply to the relevant ports when the visitor arrived and restore it on her departure.
Virtual cells
The chosen topology was not the only clever design technique employed by the university. Turnbull said he chose to base the network on switches and access points from Foundry Networks, a much smaller vendor than market leader Cisco, but one with a considerable customer base in the UK.
One of the features of Foundry's access points is "virtual cell" technology, which helps to eliminate interference between access points. Normally, access points based on the 802.11g standard — which the University of Birmingham is using — are configured to work on one of three non-overlapping channels: 1, 6 and 11. There are two problems with this approach.
One problem is that, if two access points working on the same channel are located near each other, they will cause interference and, therefore, degradation in network performance. For access points working on different channels, there is a delay in handing off clients from one access point to the other while the client reassociates and gains a new IP address.
Virtual-cell technology gets around both of these issues by allowing all the access points to run on one channel; the access points don't interfere with each other because they are managed by a central mobility controller which gives times slots to each access point and client in which they can communicate. Because all the access points work on the same channel, they appear to the client as if they are one large access point, and so the handoff time is minimal.
"With virtual cell, the client just sees one access point," said Lea. "So there is effectively zero handoff between physical access points. For VoIP activity, this is absolutely invaluable."
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