Parkervision WR1500 User Manual download pdf (Page 41)

WR1500 4-Port Wireless DSL/Cable Router

6.2 Wireless LAN Basics

6.2.1 RTS/CTS

A hidden node occurs when two stations are within range of the same Wireless Router, but

are not within range of each other. The following ﬁ gure illustrates a hidden node. Both stations

(STA) are within range of the Wireless Router (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.

When station A sends data to the WR1500 Wireless Router, it might not know that 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 deﬁ nes 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 ﬁ rst 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

conﬁ rms with the requesting station the time frame for the requested transmission.

Stations can send frames smaller than the speciﬁ ed RTS/CTS directly to the AP without the

RTS (Request To Send)/CTS (Clear to Send) handshake.

You should only conﬁ gure 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.

If the RTS/CTS 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 size.

Enabling the RTS Threshold causes redundant network overhead that could

negatively affect the throughput performance instead of providing a remedy.

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Parkervision WR1500 User Manual Page 41