CODEWITHSUNDEEP
network-programmingwifi
Christie Mathews
Christie Mathews

Reputation: 11

Why is an 802.11 Request To Send(RTS) frame Broadcast?

Wouldn't it make sense to just send the RTS to the Access Point rather than broadcast it. I understand why the Access Point broadcasts the CTS frame, so that other stations don't send packets and collision doesn't occur.

Upvotes: 1

Views: 2801

Answers (2)

Ganapathi Bhat
Ganapathi Bhat

Reputation: 157

AFAIK, RTS/CTS mechanism is a unicast sequence of 4 packets. RTS + CTS + DATA + ACK. All the stations (other than the intended target station) will extract only the header part from RTS/CTS frames, to be precise from CTS frame (they will not look into the packet details because it is a unicast packet) and get the duration field. Accordingly these stations set their NAV timer and sit idle until the timer expires.

Upvotes: 1

George
George

Reputation: 1380

In wireless networking there is a famous problem called "hidden node problem". RTS,CTS and CTS to self used in 802.11 are solutions to address hidden-node problem.

I suggest you to understnd hidden-node-problem here https://en.wikipedia.org/wiki/Hidden_node_problem

Why RTS/CST is a broadcast rather than a unicast? A broadcast will be recieved by all stations and Access-points in the range. Both RTS and CTS has a field called "duration" that includes "the time duration medium should be reserved in microseconds". All the STA's and AP's who see's this RTS/CTS will update their NAV [network-allocation-vector which is a virtual carrier sensing mechanism]. Means they will keep quiet for those many micro-seconds.

This avoids collisions.

If RTS/CTS are just directed to AP, other STA's or AP's in the visinity wont see this and may result in collisions.

Hope it helps.

Upvotes: 2

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