ZyXEL Communications G-470, User Manual

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G-470 User’s Guide
Chapter 6 Wireless Screens 57
6.2.2 SSID
The SSID (Service Set Identity) is a unique name shared among all wireless devices in a
wireless network. Wireless devices must have the same SSID to communicate with each other.
6.2.3 RTS/CTS
A hidden node occurs when two stations are within range of the same access point, but are not
within range of each other. The following figure illustrates a hidden node. Both stations are
within range of the access point (AP) or wireless gateway, but out of range of each other, so
they cannot “hear” each other; that is they do not know if the channel is currently being used.
Therefore, they are considered hidden from each other.
Figure 28 RTS/CTS
When station A sends data to the AP, it might not know that the station B is already using the
channel. If these two stations send data at the same time, collisions may occur when both sets
of data arrive at the AP at the same time, resulting in a loss of messages for both stations.
RTS/CTS is designed to prevent collisions due to hidden nodes. An RTS/CTS defines the
biggest size data frame you can send before an RTS (Request To Send)/CTS (Clear to Send)
handshake is invoked.
When a data frame exceeds the RTS/CTS value you set (between 0 to 2432 bytes), the station
that wants to transmit this frame must first send an RTS (Request To Send) message to the AP
for 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 directly to the AP without the
RTS (Request To Send)/CTS (Clear to Send) handshake.
You should only configure RTS/CTS 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.