CNET WNUD1150H, User Manual

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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 "heart-
beat" 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).
28. 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.
29. WPA2
It is the second generation of WPA. WPA2 is based on the final IEEE 802.11i amendment to the 802.11 stand-
ard.
30. Temporal Key Integrity Protocol (TKIP)
The Temporal Key Integrity Protocol, pronounced tee-kip, is part of the IEEE 802.11i encryption standard for
wireless LANs. TKIP is the next generation of WEP, the Wired Equivalency Protocol, which is used to secure
802.11 wireless LANs. TKIP provides per-packet key mixing, a message integrity check and a re-keying mech-
anism, thus fixing the flaws of WEP.
31. 802.1x Authentication
802.1x 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 di-
al-up authentication with Point-to-Point Protocol in RFC 2284. Beyond encapsulating EAP packets, the 802.1x
standard also defines EAPOL messages that convey the shared key information critical for wireless security.
32. Advanced Encryption Standard (AES)
Security issues are a major concern for wireless LANs, AES is the U.S. government’s next-generation cryptog-
raphy algorithm, which will replace DES and 3DES.