Heathrow Airport Terminal 5, opened by the Queen last week and due to welcome passengers at the end of the month, is in many ways a controversial building. However, there's no denying the grandiose scale of the £4.3 billion project. Britain's largest free-standing building, it contains a mega-shopping complex, an advanced baggage handling system... and a nifty wireless LAN.

The wireless LAN – and the building's whole IP network – is shared. It's used by BAA (British Airports Authority) which runs the building, as well as the only airline to use the space, BA. It's also shared by the stores and other businesses operating inside it, including a high-profile Gordon Ramsay restaurant planning to handle sales information over the WLAN. It will also be available for use by the 30 million travellers expected to pass through the building each year.

The key to that sharing is MPLS (multiprotocol label switching), originally a service provider technology, which segregates traffic so different users have their own completely separate virtual private networks: "MPLS is becoming more usual in buildings," says Alan Newbold, IP design leader at Ove Arup, the contractor that built the network for BAA. "If you need to deliver quality of service and security, there really is only one choice - MPLS."

The overall network in T5 is from Cisco, but BAA is using a wireless network overlay from Aruba.

"The WLAN could have been a no-brainer," says Newbold. "Too often WLANs have been thrown in because they are cheap and easy – but this is a serious estate." The lengthy tendering process actually goes back to a time before Cisco acquired its WLAN switch capability in the form of wireless startup Airespace.

The network will have 800 access points connected to two separate redundant Aruba Mobility Controller wireless switches, in two separate locations in Heathrow. The APs used are Aruba's 802.11abg devices. The new 802.11n specification was too risky and early at the time the network was designed – "but we can just clip in 802.11n when we need it", says Newbold.

The wireless LAN will be used for the baggage-handling system. Engineers with laptops and PDAs can manage the infrastructure and check barcodes on luggage anywhere in the building.

It's not seamless

However, Newbold made a deliberate decision not to focus on making the WLAN "seamless". He explains, "It's not a contiguous medium, it's not connection oriented." For instance, when staff step from the shopping mall to "back of house", it is very important that they experience a transition, and some resources are not available the other side of the line. Sometimes this is enforced by excluding radio signals from other parts of the space. "There are a lot of Faraday cage materials in the building."

Despite this deliberate limitation, the wireless LAN can support VoIP, and Newbold expects some applications to rely on it – as well as travellers to use Skype. "They should be able to use Skype through check-in to seating, although security might have something to say about that."

The control of radio signals extends beyond Wi-Fi, with an in-building distributed antenna system (DAS) handling cellular and other radio signals.

The LAN also covers an area around the terminal – and could be extended across the tarmac in future.

Although the Aruba kit can be used for mesh deployments, Arup stuck with a wired topology. "Inside the building we could get cables where we wanted because it's a new building," says Newbold. If the WLAN is extended further outside the building, that would probably be handled by mesh, he says: "It's a big benefit, making links across an airfield without having to dig the tarmac up."

"The key things Aruba offered were integrated security, a vendor that is really investing in a wireless LAN product set, scalability, decent APs with good radio propagation and integration with a good network management system to prove it is performing as it should," he said.

Each access point can serve up to 25 people, and Newbold hopes to give every user a "broadband experience" including the commercial users in the seating areas.

Will it work?

Despite careful planning, Newbold can't be sure the WLAN will work straight away, because the building has not yet seen a full complement of visitors. "Optimisation is the biggest challenge," he explains. On an average day, the building expects to see 53,000 people, all of whom will have a definite effect on the propagation of radio signals, since they are mostly made of water.

So far, on practice days, the terminal has held up to 2,000 people. To make the planning more tricky, Newbold points out that the usage pattern on day one is likely to be very different, with regular patterns only emerging over the first year or so.

Not every possible application is going onto the WLAN. Heathrow's security demands are too high to run CCTV on the WLAN. By definition, CCTV over wireless isn't exactly CCTV, he points out, because the wireless medium isn't guaranteed, and is not a closed circuit. "Critical monitoring applications need a guaranteed medium, and that means wired," he says. "At any point, someone could make a denial of service attack on a wireless LAN so you can't rely on it for live security."

CCTV images are carried over the IP network, using their own dedicated MPLS "cloud" he explains. However, they might also be exported over the Wi-Fi, to get them to security staff on PDAs so they can monitor special cases around the site.

There's no location tracking and presence awareness yet, either. "We didn't want to open T5 with a whole lot of bells and whistles which no-one had tried," says Newbold. “We needed to get it working first and and then introduce the sophisticated applications."

For BAA, the next step is to take the technology to other locations: moving BA to T5 has emptied Terminal 4, which will get an upgrade involving, among other things, 110 Aruba APs, according to Newbold. There, and elsewhere in BAA's estate, Aruba kit will be put in to replace existing systems from Motorola-owned Symbol.