Specifications

CHAPTER 9

Wireless LANs in a Campus Network

Service Set Identifiers (SSID)

An SSID maps to a VLAN and can be used to segment users into groups requiring different security or QoS treatment.

SSIDs can be broadcast by the access point or statically configured on the client, but the client must have the same SSID

as the AP to register with it. SSID names are case sensitive. When multiple SSIDs/VLANs are used on an AP, the wired

connection back to the network must be a trunk to carry all the VLANs.

WLAN Topologies

The use of wireless products falls into three categories:

n Client access, which allows mobile users to access the wired LAN resources

n Wireless connections between buildings

n Wireless mesh

Wireless connections can be made in ad-hoc mode or infrastructure mode. Ad-hoc mode (or Independent Basic Service

Set [IBSS]) is simply a group of computers talking wirelessly to each other with no access point (AP). It is limited in

range and functionality. Infrastructure mode’s BSS uses one AP to connect clients. The range of the AP’s signal, called its

microcell, must encompass all clients. The Extended Service Set (ESS) uses multiple APs with overlapping microcells to

cover all clients. Microcells should overlap by 10–15 percent for data and 15–20 percent for voice traffic. Each AP should

use a different channel. “Pico” cells, with even smaller coverage areas, can also be used.

Workgroup bridges connect to devices without a wireless network interface card (NIC) to allow their access to the wire-

less network.

Wireless mesh networks can span large distances because only the edge APs connect to the wired network. The interme-

diate APs connect wirelessly to multiple other APs and act as repeaters for them. Each AP has multiple paths through the

wireless network. The Adaptive Wireless Path (AWP) protocol runs between APs to determine the best path to the wired

network. APs choose backup paths if the best path fails.

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CCNP SWITCH 642-813 Quick Reference by Denise Donohue

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