Atlanta's airport is now saturated with wireless connectivity, serving travelers and employees.

In January, Hartsfield-Jackson Atlanta International, one of the busiest airports in the nation, threw the switch on the second of two wireless networks that blanket all concourses and gates. The system uses fibre, shielded coaxial cable and hardware from LCG Wireless to distribute cellular signals from carrier base stations to ceiling-mounted antennas throughout the airport.

The cell coverage complements an airport-wide public wireless LAN (WLAN), which went live last October.

"We needed an infrastructure to support voice, video and data services throughout the entire airport, both wired and wireless," says Lance Lyttle, the airport's CIO. Users include travelers, airport tenants such as airlines, concessions and airport employees.

Two networks needed
The solution was to create two neutral host systems. The airport acts as a landlord, building and maintaining both networks, which can be used by several carriers or service providers.

The idea behind distributed antenna systems (DAS), such as that of LGC Wireless, is to bring high-quality cell signals to every nook and cranny of large structures. For Hartsfield, that means covering nearly 6 million square feet. Today, Cingular, MetroPCS, T-Mobile and Verizon offer voice and data service over this DAS infrastructure. Some have begun to deploy advanced 3G services over the system.

The carriers installed their base stations at an airport site dubbed the telcom hotel. There, the radios are plugged into LCG's Main Hub, which converts the radio energy into an optical signal. That signal runs through a fibre web to remote hubs, which convert the signal back into radio frequency energy. Shielded coaxial cable carries the signal from a hub to several remote access units, which are like access points for cellular, mounted in the ceiling to cover a specific area.

The deployment was straightforward and smooth, says Daver Malik, wireless voice engineer for the airport's IT group. Technically, the main challenge was making sure the cell signals, covering different parts of the spectrum, didn't interfere with each other, Malik says. LGC's architecture minimises the impact if any DAS component fails, and the blades in the Main Hub can be quickly replaced if necessary, Malik says.

The DAS infrastructure will also be used by city, state and federal public safety staff and emergency responders. The 851-869MHz band is reserved for this use, so emergency crews can sidestep the public cellular bands.

The WLAN also was straightforward, though it entailed laying a lot of new Ethernet cable. The cabling connects 151 Cisco 1230 802.11b/g access points to Cisco 2000 and 3000 switches, says Dennis Rose, the airport's technical services manager.

Following Cisco's acquisition last year of Airespace, which helped pioneer the use of WLAN switches or controllers, the airport IT staff launched a redesign of the WLAN. A controller-based architecture creates a central point for securing and managing large WLANs.

Next month, Rose's team will start downloading new Cisco code to the existing access points so they can communicate with the Cisco controllers to be installed in the data center.

Today, four Wi-Fi Internet providers offer service to Hartsfield passengers over the WLAN: Access Anyplace, Boingo, Concourse and Sprint.

Workers access anywhere
Employees jump on the WLAN whenever they need to. But the airport requires not only a valid username and password, but also a registered media access control (MAC) address, before the employee is granted access. A Cisco RADIUS server handles authentication for the WLAN, and then hands off authentication information to the corporate RADIUS server so WLAN users can access services on the backbone.

Airport laptops have Verizon-branded Sierra Wireless AirCards so that users can make a data connection, over a VPN, if they're beyond the range of the WLAN.

Passengers logging on to the WLAN are segregated on a separate virtual LAN (VLAN). Some of them access the Internet via the WLAN home page. But subscribers to one of the airport's Wi-Fi providers can launch their provider's client application, bypassing the airport Web page.

Rose's team relies on AirDefense's AirDefense Enterprise software and radio-frequency sensors to monitor the WLAN frequencies, detect unauthorised radios and block them.

Administrators see one to 10 deliberate attacks daily, usually travelers that have equipped a wireless laptop with sniffer software for probing WLANs. "We can notice these with the AirDefense software, but they're not affecting our network," Rose says.

The WLAN and the distributed antenna system are designed to host multiple service providers. And for both systems, the most complex issues were about accommodating the differing business models and service plans of the various carriers and providers.