PLANET WNL-U554A - Manual (Page 60)

150Mbps 802.11n Wireless USB Adapte r
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the data packet size exceeds the defined RTS threshold. With the CSMA/CA transmission
mechanism, the transmitting station sends out an RTS packet to the receiving station, and
waits for the receiving station to send back a CTS (Clear to Send) packet before sending the
actual packet data. This setting is useful for networks with many clients. With many clients, and
a high network load, there will be many more collisions. By lowering the RTS threshold, there
may be fewer collisions, and performance should improve. Basically, with a faster RTS
threshold, the system can recover from problems faster. RTS packets consume valuable
bandwidth, however, so setting this value too low will limit performance.
27. 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).
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 standard.
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 mechanism, 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 dial‐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 cryptography algorithm, which will replace DES and 3DES.