Wireless in large enterprises
Monday, April 24, 2006 11:07 AM
In this final installment of our wireless networking series, we take a look at large-scale enterprise switched wireless LANs.
Figure A
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Switched Wireless LANs are the latest advancement in wireless networking where simplified Access Points are controlled by a centralized Wireless Controller. Data is passed and managed through these centralized Wireless Controllers from manufacturers like Cisco (via Airespace acquisition), Aruba Networks, Symbol, and Trapeze Networks. The Access Points in this case have a simpler operating system designed to be of minimal complexity and the more complex logic is embedded in the Wireless Controller. The Access Points usually don't physically connect to the Wireless Controllers, but they're logically switched or routed through the Wireless Controllers. To support multiple VLANs, data is encapsulated in to a tunnel of some sort so that there is a direct logical connection from the Access Point to the Wireless Controller even if the devices are on different subnets.
From a management standpoint, the administrator only needs to manage the Wireless LAN controller which in turn can control hundreds of Access Points. These Access Points can use certain custom DHCP attributes to figure out where the Wireless Controller is and automatically link to it to become an extension of the Controller. This vastly improves the scalability of switched Wireless LANs because additional Access Points are essentially plug and play. For multi-VLAN support, the Access Points no longer need a special VLAN trunking port on the switch where it connects to and can use any old access port on any Switch or even Hub which eases manageability. The VLAN data is encapsulated and sent to the central Wireless Controller where it handles a single high speed multi-VLAN connection to the core network Switch. Security management is also consolidated because all Access Control and Authentication is handled at the centralized Controller rather than having it on each Access Point. Only the centralized Wireless Controller needs to be tied in to the RADIUS server which in turn is tied in to Active Directory in the example shown in Figure A.
Another benefit of a Switched Wireless LAN is low-latency roaming. This allows latency sensitive applications like VoIP and Citrix. Cut-over times can happen in as 50 milliseconds which are mostly unnoticeable. Traditional Wireless LANs where each Access Point is configured independently have cut-over times in the 1000 millisecond range which can ruin phone calls and drop application sessions on Wireless devices. The main downside to Switched Wireless LANs is the additional cost because of the additional expense of the Wireless Controller. But in large Wireless LAN deployments, these additional costs can easily be offset by the ease of manageability.
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