ZyXEL Communications Prestige 661H Series, User Manual

Page: 506 / 547

Prestige 661H/HW Series User’s Guide
Appendix L Wireless LANs 506
A large Fragmentation Threshold is recommended for networks not prone to interference
while you should set a smaller threshold for busy networks or networks that are prone to
interference.
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
A preamble is used to synchronize the transmission timing in your wireless network. There are
two preamble modes:
Long and Short .
Short preamble takes less time to process and minimizes overhead, so it should be used in a
good wireless network environment when all wireless stations support it.
Select Long if you have a ‘noisy’ network or are unsure of what preamble mode your wireless
stations support as all IEEE 802.11b compliant wireless adapters must support long preamble.
However, not all wireless adapters support short preamble. Use long preamble if you are
unsure what preamble mode the wireless adapters support, to ensure interpretability between
the AP and the wireless stations and to provide more reliable communication in ‘noisy’
networks.
Select Dynamic to have the AP automatically use short preamble when all wireless stations
support it, otherwise the AP uses long preamble.
Note: The AP and the wireless stations MUST use the same preamble mode in order
to communicate.
IEEE 802.11g Wireless LAN
IEEE 802.11g 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. The IEEE 802.11g data rate and modulation
are as follows:
Table 185 IEEE 802.11g
DATA RATE (MBPS) MODULATION
1 DBPSK (Differential Binary Phase Shift Keyed)
2 DQPSK (Differential Quadrature Phase Shift Keying)
5.5 / 11 CCK (Complementary Code Keying)
6/9/12/18/24/36/48/54 OFDM (Orthogonal Frequency Division Multiplexing)