Controller Based WLANs

What is the best fix for a hidden node issue?

Product and Software: This article applies to all ArubaOS versions.

 

"Hidden node" refers to the situation when two wireless devices are unable to hear one another's transmissions. Consider a point-to-multipoint outdoor mesh network, with two mesh points on opposite sides of the mesh portal. If the mesh points are widely separated, hidden node is a possibility because the two mesh points are in range of the portal, but out of range of each other. In this case, they may attempt to transmit simultaneously, which results in a collision at the portal and an inability to decode either transmission.

 

This situation is what the Request to Send/Clear to Send (RTS/CTS) is for. This setting is specified via the RTS Threshold setting in the Aruba controller. If a hidden node problem is suspected (that is, lower throughput/performance than predicted and you have two or more nodes that are possibly out of range of each other) try lowering the RTS threshold 500 bytes, or even 250. This effectively turns on RTS, which is off by default.

 

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When RTS/CTS is enabled on an AP group, all nodes in that group will transmit an RTS frame and wait for a subsequent CTS response before sending. This ensures that all nodes receive the message, at the cost of reduced performance due to the channel management overhead.

 

RTS should not be needed if the two mesh points are within range of each other, even if only at the lowest data rate but are linked to the portal at a much higher rate. This problem should only appear if the two points are truly out of range or obstructed from each other.

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‎07-02-2014 01:19 AM
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