London's Heathrow Airport Terminal 5 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.