There is certainly a need for centralized control in wireless deployments today. Initial wireless deployments were based on standalone access points called autonomous access or fat APs. An autonomous AP is one that does not rely on a central control device. Al- though this is a great start, the problem lies in scalability. Eventually, you will have prob- lems keeping your configurations consistent, monitoring the state of each AP, and actually taking action when a change occurs. You end up with holes in your coverage area, and there is no real dynamic method to recover from that. There is certainly a need for central- ized control, and the Cisco Unified Wireless Network (CUWN) is based on centralized control.
Eventually you will want or need to convert those standalone APs, if possible, to light- weight APs. A lightweight AP is managed with a controller.
Traditionally after a site survey, you would deploy your wireless network based on the in- formation you gathered. As time passes, the environment you did the original site survey in will change. These changes, although sometimes subtle, will affect the wireless cover- age. The CUWN addresses these issues.
The Cisco Solution
The CUWN solution is based on a centralized control model. Figure 10-1 illustrates the numerous components of the CUWN.
An AP operating in lightweight mode gets its configuration from the controller. This means that you will perform most of your configuration directly on the controller. It dy- namically updates the AP as the environment changes. This also allows all the APs to share a common configuration, increasing the uniformity of your wireless network and eliminat- ing inconsistencies in your AP configurations.
As you can see, five functional areas exist:
- Wireless clients
- Access points
- Network unification
- Network management
- Network services
Supporting Multiple Networks
Previous chapters discussed that an AP can actually advertise multiple SSIDs, which lets the AP offer guest access as well as corporate user access and maybe even access for wire- less IP phones. Each Wireless LAN Controller actually can support 512 different VLAN instances. Remember that on the connection between the AP and the Wireless LAN Con- troller, all your wireless client data is passed via the LWAPP tunnel as it travels toward the wired domain.
To review, recall that an SSID exists only in the wireless space. An SSID is then tied to a VLAN within the controller. Each lightweight AP can support 512 different VLANs, but you don’t very often see that many on one AP.
On the other hand, your Wireless LAN Controller can have up to 16 wireless LANs (WLAN) tied to each AP. Each WLAN is assigned a wireless LAN identification (WLANID) by the controller. This is a number between 1 and 16, and you don’t get to choose which one to use.
So, now you have a WLAN that brings together the concept of an SSID on the wireless space and a VLAN on the wired space. By having separate WLANs, you can assign differ- ent quality-of-service (QoS) policies to the type of traffic encountered on each of them. An example of this would be to have a WLAN for IP Phones and a different WLAN for regular network users.
Each AP supports up to 16 SSIDs; generally, one SSID is mapped to one VLAN. With that said, even though a Wireless LAN Controller can support up to 512 VLANs per AP, you see a maximum of only 16 VLANs in most situations.
The CUWN Architecture
The Cisco Unified Wireless Network defines a total of five functional areas or intercon- nected elements, as shown in Figure 10-2.
The five elements or components all work together. It’s no longer about point products, where you can buy a standalone AP and deploy it and then later get management software to handle it. Today it is all about everything working together to create a smarter, more functional net- work. To illustrate how it all comes together, consider a Cisco wireless network. This type of network includes the following wireless clients (the first component of the CUWN):
- Cisco Aironet client devices
- Cisco-compatible client devices (not necessarily Cisco products, but still compatible)
- Cisco Secure Services Client (SSC)
The client devices get a user connected.
The second component, the access point, is dynamically managed by your controllers, and they use LWAPP to communicate. The AP bridges the client device to the wired net- work. A number of APs that could be discussed here are as follows:
- The 1130AG
- The 1240AG
- The 1250AG
- The 1300 series bridge
- The 1400 series bridge
- The 1500 series outdoor mesh
No comments:
Post a Comment