10.5 Wireless Network Implementation

Hub-and-Spoke

In a hub-and-spoke configuration, a wireless controller is connected to all APs through wired links. The individual APs contain very little embedded intelligence and are sometimes referred to as lightweight access points (LWAPs).

In a larger deployment, you must use higher end equipment designed to support a large number of users. Three different types of enterprise deployments have been commonly implemented, as described here:

Independent Access Points - In the early days of wireless networking, large organizations implemented independent access points through their facilities. Each AP stood alone, providing separate wireless networks by using its own independent configuration. Independent APs offered limited mobility and were difficult to manage. To enable roaming using independent access points, you must configure all access points in the network: With the same SSID. To use the same channel. To function on the same IP subnet. If you don't do these things, then mobile devices must get a new IP address every time they move to a different AP, which disrupts connectivity. Hub-and-Spoke Infrastructure - In a hub-and-spoke configuration, a wireless controller is connected to all APs through wired links. The individual APs contain very little embedded intelligence and are sometimes referred to as lightweight access points (LWAPs). The wireless controller: Manages all of the APs that are connected to it. Configuration changes are made once on the controller and are then pushed out to all connected APs. Usually provides DHCP services to dynamically assign IP addressing information to wireless clients. Connects the wireless network to the internal wired network. Routes wireless traffic from the wireless network to the internal wired network (and vice versa). The hub-and-spoke infrastructure is more efficient and allows for much larger wireless networks. However, the controller itself becomes a bottleneck. All wireless data must pass through the controller, even if it is destined for another wireless host on the same wireless network. The APs are not able to communicate directly with each other; they can communicate only with the wireless controller. If the controller goes down, the entire wireless network will cease to function even if the APs remain functional. Distributed Wireless Mesh Infrastructure - Newer wireless networks can be deployed using a distributed wireless mesh architecture. These networks still use a controller, but they move some of the network intelligence from the controller out to the individual APs. In this configuration, the controller is no longer a bottleneck. The APs are smart enough to communicate directly with each other to create more efficient data paths for network traffic. For example, if one wireless host needs to send data to another wireless host, the data moves from AP to AP using wireless links until it reaches the destination host. The controller is still used to manage, direct, and scale the network, but the work of moving data as efficiently as possible through the wireless LAN is taken care of by the individual APs. Because the links are wireless instead of wired, the APs can quickly re-associate themselves with a different wireless controller if its primary controller becomes unavailable for some reason. Many vendors allow you to configure each AP with primary, secondary, and tertiary wireless controllers to provide a high degree of redundancy. As with the hub-and-spoke architecture, a wireless controller in a distributed mesh deployment is usually the gateway to the wired network. It routes data from the wireless network to the wired network, and vice versa. For example, on Cisco wireless equipment the lightweight access point protocol (LWAPP) is used to route frames back and forth between the wireless network and the wired LAN. Wireless Bridges - Wireless bridges are used to connect wired or wireless networks together. You can create a wireless link between two buildings with a wireless bridge. Using directional antennae, a wireless signal can be transmitted directly between two buildings, connecting both LANs together. Because the wireless link is a bridge, only the frames addressed to a host on the remote LAN are forwarded across the link. Locally addressed frames remain on the local LAN.

Independent Access Points

Independent access points (APs) are where each AP stands alone, providing separate wireless networks by using its own independent configuration.

Distributed Wireless Mesh Infrastructure

Newer wireless networks can be deployed using a distributed wireless mesh architecture. These networks still use a controller, but they move some of the network intelligence from the controller out to the individual APs.

Home or small business wireless networks typically use a consumer-grade access point that combines many functions into a single device:

When implementing a wireless network, you should use the appropriate equipment for the type of deployment. Wireless access point Ethernet switch NAT router These devices work reasonably well in small environments. However, they have very limited capacity, typically supporting a maximum of 5-10 wireless clients at a time. If you connect more clients than this, the bandwidth of the entire wireless network is severely impacted.

Wireless Bridges

Wireless bridges are used to connect wired or wireless networks together.