Zyxel NBG-418N v2 - Инструкция по эксплуатации - Страница 208

Appendix E Wireless LANs

NBG-418N v2 User’s Guide

208

Fig ure  1 4 6    

 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/ C TS

 is designed to prevent collisions due to hidden nodes. An 

RTS/ C TS 

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/ C TS 

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/ C TS 

directly to the AP without the RTS (Request 

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

You should only configure 

RTS/ C TS

 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/ C TS

 value is greater than the 

Fra g m e nta tio n Thre sho ld

 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/ C TS

 size. 

Note: Enabling the RTS Threshold causes redundant network overhead that could negatively 

affect the throughput performance instead of providing a remedy.

Fra g m e nta tio n Thre sho ld

A 

Fra g m e nta tio n Thre sho ld

 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 

Fra g m e nta tio n Thre sho ld

 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 

Fra g m e nta tio n Thre sho ld

 value is smaller than the 

RTS/ C TS

 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/ C TS 

size.