User's Manual

4.12 What is Beacon Interval?
In addition to data frames that carry information from higher layers, 802.11 includes management and control frames
that support data transfer. The beacon frame, which is a type of management frame, provides the "heartbeat" of a
wireless LAN, enabling stations to establish and maintain communications in an orderly fashion.
Beacon Interval represents the amount of time between beacon transmissions. Before a station enters power save mode,
the station needs the beacon interval to know when to wake up to receive the beacon (and learn whether there are
buffered frames at the access point).
4.13 What is Preamble Type?
There are two preamble types defined in IEEE 802.11 specification. A long preamble basically gives the decoder more
time to process the preamble. All 802.11 devices support a long preamble. The short preamble is designed to improve
efficiency (for example, for VoIP systems). The difference between the two is in the Synchronization field. The long
preamble is 128 bits, and the short is 56 bits.
4.14 What is SSID Broadcast?
Broadcast of SSID is done in access points by the beacon. This announces your access point (including various bits of
information about it) to the wireless world around it. By disabling that feature, the SSID configured in the client must
match the SSID of the access point.
Some wireless devices don't work properly if SSID isn't broadcast (for example the D-link DWL-120 USB 802.11b
adapter). Generally if your client hardware supports operation with SSID disabled, it's not a bad idea to run that way to
enhance network security. However it's no replacement for WEP, MAC filtering or other protections.
4.15 What is Wi-Fi Protected Access (WPA)?
Wi-Fi's original security mechanism, Wired Equivalent Privacy (WEP), has been viewed as insufficient for securing
confidential business communications. A longer-term solution, the IEEE 802.Hi standard, is under development.
However, since the IEEE 802. Hi standard is not expected to be published until the end of 2003, several members of the
Wi-Fi Alliance teamed up with members of the IEEE 802. Hi task group to develop a significant near-term enhancement
to Wi-Fi security. Together, this team developed Wi-Fi Protected Access.
To upgrade a WLAN network to support WPA, Access Points will require a WPA software upgrade. Clients will require
a software upgrade for the network interface card, and possibly a software update for the operating system. For
enterprise networks, an authentication server, typically one that supports RADIUS and the selected EAP authentication
protocol, will be added to the network.
4.16 WhatisWPA2?
It is the second generation of WPA. WPA2 is based on the final IEEE 802.1H amendment to the 802.11 standard.
4.17 What is 802.lx Authentication?
802.lx is a framework for authenticated MAC-level access control, defines Extensible Authentication Protocol (EAP)
over LANs (WAPOL). The standard encapsulates and leverages much of EAP, which was defined for dial-up
authentication with Point-to-Point Protocol in RFC 2284.
Beyond encapsulating EAP packets, the 802. lx standard also defines EAPOL messages that convey the shared key
information critical for wireless security.
- 57 -