Wireless Full duplex.

Unanswered Question
Dec 4th, 2009

Dear All.

I want some information on cisco wireless, does it support full duplex wireless.

Some other wireless company says, there wireless are full duplex wireless.

I am also looking for some information on how full duplex wireless work.

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Overall Rating: 5 (2 ratings)
Leo Laohoo Fri, 12/04/2009 - 23:21

Unfortunately, wireless is half duplex.  When a wireless device transmits everyone stops and listens.  The only full duplex is the wired link.

George Stefanick Sat, 12/05/2009 - 07:12

As Leo points out. A wireless AP is like a HUB in the air. The medium works on CSMA-CA. Only one client can occupy the channel at a time.

chopra.harish1 Tue, 04/03/2012 - 22:03

Hi Scott,

I completely aggree with you, that Wireless is Half duplex since it uses the complete channel at one time and rest of the clients just listen to the traffic for their turns. I have read the CSMA/CA as well that how does it works.

My query is - When using applications like Torrent, it shows the download and upload happening at the same time. How come it is possible ? Is it just that we see but actually doesn't happen at the backend ?

Can you share some good document or link to make it more clear to me.

Thank you !



chopra.harish1 Tue, 04/03/2012 - 22:17

Also, One more querry - Once the medium is reserved by a Client for the frame duration value and rest of the clients increases their NAV and starts counting down.

What will happen if the Client A gets shuts down in while sending the traffic to AP. Will the Rest of clients like Client B will initiate sending traffic to AP or Will complete its Count down of NAV ?

Leo Laohoo Tue, 04/03/2012 - 22:18
When using applications like Torrent, it shows the download and upload happening at the same time.

How many clients are connected to the same WAP and seeding Torrent?  One?  Two?  Get a dozen and you'll see. 

Leo Laohoo Tue, 04/03/2012 - 22:32
around 10 clients and using torrent

You should see effects of your wireless when you are all seeding and downloading something popular.

Geez, I sure don't want to know what the cycle rate is.

What kind of ethernet uplink does the WAP have?

Amjad Abdullah Wed, 04/04/2012 - 02:46


You said "" Is it just that we see but actually doesn't happen at the backend ?""

this is 100% correct. The half-duplex between you and the AP is very fast (microseconds) so say every 30 micro seconds one can send and no-one except this one can send and all should wait for him/her to finish sending. after s/he finish other clients will try to to send (one at a time). so for 1 second many clilents can send multiple times. This is how it goes. For your torrent it shows you the bandwidth in layer 3 speed. it just cares about how much data you send and receive in a second. (this is why it is kbps: Kilobit per SECOND). This means the total effective speed you are allowed to send/receive in one second. This transmission is not done continuously in layer 2 because you have a few microseconds everytime you'd like to send. but in total you are able to send with X speed in one second.

Got it?

Hope this is clear enough to you.


George Stefanick Wed, 04/04/2012 - 15:28

Not to throw a wrench in this .. But 80211ac will allow for full duplex like connections

Just an FYI

Sent from Cisco Technical Support iPhone App

Amjad Abdullah Fri, 04/06/2012 - 23:57


I think 802.11ac is going to support full duplex like connections because both senders and receivers have multiple

antennas (MIMO). For example; an STA will have two antennas, one for sending and one for receiving. the send/receive processes will be done on different channels (or different spatial streams). Having about 160 MHz of channel width will make it easy to achieve this.

George Stefanick Tue, 01/29/2013 - 10:17

So is time travel ..

"Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin
‎"I'm in a serious relationship with my Wi-Fi. You could say we have a connection."


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