ZyXEL Communications NWA1120 Series User Manual page 191

If the Fragmentation Threshold value is smaller than the RTS/CTS value (see previously) you
set then the RTS (Request To Send)/CTS (Clear to Send) handshake will never occur as data frames
will be fragmented before they reach RTS/CTS size.
Preamble Type
Preamble is used to signal that data is coming to the receiver. Short and long refer to the length of
the synchronization field in a packet.
Short preamble increases performance as less time sending preamble means more time for sending
data. All IEEE 802.11 compliant wireless adapters support long preamble, but not all support short
preamble.
Use long preamble if you are unsure what preamble mode other wireless devices on the network
support, and to provide more reliable communications in busy wireless networks.
Use short preamble if you are sure all wireless devices on the network support it, and to provide
more efficient communications.
Use the dynamic setting to automatically use short preamble when all wireless devices on the
network support it, otherwise the NWA uses long preamble.
Note: The wireless devices MUST use the same preamble mode in order to communicate.
Wireless LAN Standards
The IEEE 802.11b wireless access standard was first published in 1999. IEEE 802.11b has a
maximum data rate of 11 Mbps and uses the 2.4 GHz band.
IEEE 802.11g also works in the 2.4 GHz band and is fully compatible with the IEEE 802.11b
standard. This means an IEEE 802.11b adapter can interface directly with an IEEE 802.11g access
point (and vice versa) at 11 Mbps or lower depending on range. IEEE 802.11g has several
intermediate rate steps between the maximum and minimum data rates (54 Mbps and 1 Mbps
respectively).
IEEE 802.11a has a data rate of up to 54 Mbps using the 5 GHz band. IEEE 802.11a is not
interoperable with IEEE 802.11b or IEEE 802.11g.
IEEE 802.11n can operate both in the 2.4 GHz and 5 GHz bands and is backward compatible with
the IEEE 802.11a, IEEE 802.11b, and IEEE 802.11g standards. It improves network throughput and
increases the maximum raw data rate from 54 Mbps to 300 Mbps by using multiple-input multiple-
output (MIMO), a channel width of 40 MHz, frame aggregation and short guard interval.
Table 55 Wireless LAN Standards Comparison Table
WIRELESS LAN
STANDARD
IEEE 802.11b
IEEE 802.11g
NWA1120 Series User's Guide
MAXIMUM NET FREQUENCY
DATA RATE BAND
11 Mbps
54 Mbps
COMPATIBILITY
IEEE 802.11g
2.4 GHz
IEEE 802.11n
IEEE 802.11b
2.4 GHz
IEEE 802.11n
Appendix E Wireless LANs
191