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Planning for the wireless network

Basic planning considerations.

If you think that planning for a wireless LAN infrastructure is just an extension of planning for your wired LAN, think again. When users get untethered from their desks, things change, and they change a lot. Suppose, just for an example, that a user moves from his desk to a conference room that's served by a new access point, turns on his computer and tries to log on to the WLAN. Where do his credentials get authenticated? And that's just the first question.

This tip, which is excerpted from "The Wireless LAN Book for Enterprises," published by Trapeze Networks, offers some things to think about.

Wireless users are focused on gaining access to vital business applications, file servers, email and the Internet while working anywhere -- not just at their desks. However, users won't be happy if throughout slows to a trickle. Recent corporate IT upgrades from shared to switched media at the network edge have raised user expectations to the high-performance network experience that switched 100 Mbps desktop links provide.

As wireless deployments increase, the minimal "Can-you-hear-me-now" approach to delivering only coverage won't work. Instead, IT organizations must plan for capacity by designing a WLAN that ensures enough bandwidth for each mobile user. Enforcing CoS over WLANs does not guarantee performance, so IT managers must understand the impact that the shared infrastructure will have on certain applications.

IT organizations must also take care not to accidentally create a performance bottleneck by using appliances to solve the wireless problems of security and mobility. Most appliances that provide secure roaming are traditional servers that throttle performance, because they must process all wireless traffic. Other systems provide only basic connectivity information -- simply telling users whether or not they're attached to the network. This information yields no insight into the actual throughput of the connection.

In wired networks, most network engineering tools are based on geography and physical devices. Subnets are assigned to router or switch ports, VLANs belong to specific subnets, and ACLs and multicast protocols reside on routers.

Because wireless networks require user mobility, network attributes can no longer be based on physical ports or device location. To enable consistent VLAN and subnet membership, to apply appropriate ACLs to users, and to deliver multicast services, the entire network must be planned as one cohesive system, supporting network policies that span the wired and wireless domains. Cohesive policies cannot be delivered across the network if the WLAN is managed as a separate infrastructure from the wired LAN.

You can download "The Wireless LAN Book for Enterprises" at

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