H3C Technologies H3C WX3000E Series Wireless Switches - Manual (Page 23)

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Generally, an AP can provide more than one ESS at the same time. The configuration of ESS is distributed
mainly from AC to AP, and the AP can broadcast the current information of ESS by beacon or probe
response frames. Clients can select an ESS in which it is interested to join.
Different ESS domains can be configured on the AC. The AC can be configured to allow associated APs
to accept clients in these ESS domains once their credentials are accepted.
Centralized WLAN
Centralized WLAN is a unified solution for wireless local area networks. Figure 11 shows a centralized
WLAN network.
Figure 11 Centralized WLAN network
In this network, there are two ACs and three APs. An AP can connect with an AC directly, or over a Layer
2 or Layer 3 network. The other AC serves as the backup.
During initialization, an AP obtains its basic network configuration parameters, such as its own IP
address, gateway address, domain name and DNS server address from a DHCP server.
An AP uses a discovery mechanism to locate the AC. For example, using the unicast discovery
mechanism, the AP can request the DNS server to provide the IP address of the AC.
The following describes a basic communication process in the centralized WLAN network.
1. A client gets associated with an AP in the network.
2. The AP communicates with the AC for authenticating the client's credential.
3. The AC contacts the authentication server (AS) to authenticate the client.
Once the wireless client passes authentication, it can access authorized WLAN services and
communicate with other wireless clients or wired devices.