ZyXEL Communications G-220 Manuel D’Utilisation
ZyAIR G-220 User’s Guide
2-6
Wireless LAN Network
permission to send it. The AP then responds with a CTS (Clear to Send) message to all other stations within
its range to notify them to defer their transmission. It also reserves and confirms with the requesting station
the time frame for the requested transmission.
Stations can send frames smaller than the specified RTS/CTS Threshold directly to the AP without the
RTS (Request To Send)/CTS (Clear to Send) handshake.
You should only configure RTS/CTS Threshold if the possibility of hidden nodes exists on your network
and the “cost” of resending large frames is more than the extra network overhead involved in the RTS
(Request To Send)/CTS (Clear to Send) handshake.
If the RTS/CTS Threshold value is greater than the Fragmentation Threshold value (see next), 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 Threshold size.
its range to notify them to defer their transmission. It also reserves and confirms with the requesting station
the time frame for the requested transmission.
Stations can send frames smaller than the specified RTS/CTS Threshold directly to the AP without the
RTS (Request To Send)/CTS (Clear to Send) handshake.
You should only configure RTS/CTS Threshold if the possibility of hidden nodes exists on your network
and the “cost” of resending large frames is more than the extra network overhead involved in the RTS
(Request To Send)/CTS (Clear to Send) handshake.
If the RTS/CTS Threshold value is greater than the Fragmentation Threshold value (see next), 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 Threshold size.
Enabling the RTS Threshold causes redundant network overhead that could
negatively affect the throughput performance.
2.5 Authentication
Type
The IEEE 802.11b standard describes a simple authentication method between the wireless stations and
AP. Three authentication modes are defined: Auto, Open System and Shared Key.
Open System mode is implemented for ease-of-use and when security is not an issue. The wireless station
and the AP do not share a secret key. Thus the wireless stations can associate with any AP and listen to any
data transmitted plaintext.
Shared Key mode involves a shared secret key to authenticate the wireless station to the AP. This requires
you to enable the WEP encryption and specify a WEP key on both the wireless station and the AP.
Auto authentication mode allows the ZyAIR to switch between the open and shared key authentication
modes automatically. Use the auto mode if you do not know the authentication mode of the other wireless
stations.
AP. Three authentication modes are defined: Auto, Open System and Shared Key.
Open System mode is implemented for ease-of-use and when security is not an issue. The wireless station
and the AP do not share a secret key. Thus the wireless stations can associate with any AP and listen to any
data transmitted plaintext.
Shared Key mode involves a shared secret key to authenticate the wireless station to the AP. This requires
you to enable the WEP encryption and specify a WEP key on both the wireless station and the AP.
Auto authentication mode allows the ZyAIR to switch between the open and shared key authentication
modes automatically. Use the auto mode if you do not know the authentication mode of the other wireless
stations.
2.6 Preamble
Type
A preamble is used to synchronize the transmission timing in your wireless network. There are two
preamble modes: Long Preamble and Short Preamble.
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 Preamble if you have a ‘noisy’ network or are unsure of what preamble mode the access point
or the other 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 ZyAIR and the
access point/wireless stations and to provide more reliable communication in ‘noisy’ networks.
preamble modes: Long Preamble and Short Preamble.
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 Preamble if you have a ‘noisy’ network or are unsure of what preamble mode the access point
or the other 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 ZyAIR and the
access point/wireless stations and to provide more reliable communication in ‘noisy’ networks.