Microsoft has ditched Cisco in favour of WLAN start-up Aruba, as it upgrades one of the world's largest wireless LAN (WLAN) installations from old-fashioned fat access points.

Microsoft is taking out around 5,000 Cisco Aironet access points, and upgrading to an Aruba wireless switch system which will use five thousand thin access points to support 25,000 simultaneous WLAN users, in 277 buildings round the world.

The announcement will be a disappointment to Cisco, as its purchase of Aruba's rival Airespace was supposed to offer an upgrade path for customers like Microsoft who needed a centrally-managed wireless LAN system.

"This will surprise many spectators - including myself," said Richard Webb, wireless anayst at Infonetics Research. "People said that WLAN was a done deal, and large customers would automatically go to Cisco. They'll have to view Aruba in a new light, and some people will be raising eyebrows at the money Cisco paid for Airespace."

In fact, Cisco's efforts to integrate Airespace and provide an upgrade path have been lacklustre, while Aruba and its other main rival, Trapeze, have continued to innovate.

Although Aruba probably offered a very competitive price (no price has been revealed for the deal), Webb said that the deal must have been based on technical merits. "Microsoft isn't buying on price," he said. "The company is not short of money, so if Aruba weren't on the table in terms of technology, no amount of discount would have got the deal."

Security features such as Aruba's firewall and IDS may have been big factors, he said. Indeed, as we reported here a year ago, Microsoft has already been using Aruba for security. Aruba and Microsoft are also stressing support for voice on Wi-Fi, as well as guest networks that lets the office WLAN double as a hotspot for visitors.

Microsoft had extensive tests carried out by wireless test house Iometrix, and the University of New Hampshire's inter-operability lab, which covered security, scalability and performance - the results of which Aruba has promised to put on its site.

Microsoft plans to make some offices "wireless only", and will integrate the WLAN with its Network Access Protection Architecture that protects the network from infected clients. The WLAN will also support a guest access system which will allow visitors to Microsoft buildings to use the Internet.

Aruba is also keen to suggest that, as a result of this contract, it will have close links into Microsoft's future products. "Aruba plans to work with Microsoft to develop and test future software products to ensure they operate simply and easily over wireless networks," says its release. "Consequently, Aruba customers can be assured the best possible interaction and unprecedented interoperability between Microsoft products and Aruba mobility systems."