Appendix D Wireless LANs
NXC Series User’s Guide
494
Note: Enabling the RTS Threshold causes redundant network overhead that could negatively
affect the throughput performance instead of providing a remedy.
Fragmentation Threshold
A Fragmentation Threshold is the maximum data fragment size (between 256 and 2432 bytes) that can
be sent in the wireless network before the AP will fragment the packet into smaller data frames.
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
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 NXC uses short preamble.
Note: The wireless devices 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 234 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)
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