CMU anticipates four major integration issues with its dual-WLAN approach.

Issue 1: integrating network architectures

One reflects the different architectures of the two vendors, Aruba with its centralized approach, Xirrus with a more distributed model. "We'll need to come up with a reasonable compromise between the two models," McCarriar says. For now, CMU plans to monitor traffic patterns on the two networks, and see how the gradual growth of 802.11n clients impacts the different architectures.

Issue 2: integrating authentication models

Each vendor has its own "captive" Web portal to capture a wireless user logging on, and its own authentication methods, though both are based on the 802.1X standard, which CMU is adopting for Wireless Andrew 2.0. CMU has had its own authentication portal for years. How can these be rationalized into a consistent experience for users? The geographic separation of the networks will be an advantage, because it will minimize the chance of clients physically roaming from one WLAN to the other.

CMU is exploring two options. One is co-development work with Xirrus, creating code that would let users share authentication keys between the two networks. The second option exploits Aruba's push to apply the more granular and strong wireless security controls to wired clients. McCarriar thinks it might be possible to bring all clients through the Aruba portal, which would act in effect as a front-end to Xirrus' authentication.

Issue 3: roaming

But roaming itself will be an issue, as users moving from dorms to classrooms for example, McCarrier acknowledges. How will user information, including authentication, be shifted from one Aruba to Xirrus and back again, without forcing a complete break and re-association and re-authentication? Right now, that's an unknown.

Issue 4: integrating management

As with authentication, CMU has its own home-grown network management and monitoring systems. And of course, so do the two WLAN vendors. "The big thing I'm worried about is aggregating statistics between the two platforms," McCarriar says. "That will mean some [code] development." The current idea will be to explore how to pull relevant monitoring and management data from the two brands of equipment into CMU's existing system.

Radio frequency site surveys will occupy the IT team and vendors until early 2008. Deployment is expected to start shortly after, as fast as both companies can deliver 802.11n products, and be completed by the end of 2008.