Response time on RTS/CTS handshake

[Harry May]

I have been checking the response time of the Wifi RTS/CTS handshake using different network setups.  I have noticed the time is the same, approximately 16 microseconds, no matter what the distance is between the nodes.

I have several questions:

  - Is the response automatic without any calculations as to distance?

  - Is there a procedure to generate time according to distance?

  - I know the RTS/CTS is located in the WifiRemoteStationManager module but so far I haven't been able to find it. My thought is, can I modify the module to generate the time according to distance between nodes or am I trying to do the impossible?

Thanks in advance for your response!

Harry May

[Soulimane Mammar]

Hi,

it seems that you have create a channel with YansWifiChannelHelper::Default().Create(), while this is ok for most scenarios, in your case you'll not see any significant difference since the propagation model used by default is ns3::ConstantSpeedPropagationDelayModel with a very big Propagation Speed  by default  ( 2.99792e+08 ) 

A change in distances of few meters will have almost no effect on the delay (and sometimes not even captured by the floating point arithmetic of the machine)

Regards 

[Tom Henderson]

On 2/16/22 10:55 AM, Harry May wrote:
> I have been checking the response time of the Wifi RTS/CTS handshake
> using different network setups.  I have noticed the time is the same,
> approximately 16 microseconds, no matter what the distance is between
> the nodes.
>
> I have several questions:
>   - Is the response automatic without any calculations as to distance?

As someone else responded, the propagation delay is negligible compared
to the SIFS delay. You are probably observing the SIFS delay, which
defaults to 16 us for 802.11n/ac Wi-Fi standards:

https://en.wikipedia.org/wiki/Short_Interframe_Space

See the second figure in this blog post for a graphical explanation:

https://blogs.arubanetworks.com/industries/understanding-802-11-medium-contention/

>   - Is there a procedure to generate time according to distance?

No, the delays in Wi-Fi are dominated by MAC timers and operation.

>   - I know the RTS/CTS is located in the WifiRemoteStationManager
> module but so far I haven't been able to find it. My thought is, can I
> modify the module to generate the time according to distance between
> nodes or am I trying to do the impossible?

If you search that code (WifiRemoteStationManager) for the strings 'Rts'
and 'Cts' you should be able to find it.

- Tom

[Soulimane Mammar]

Hi,

RTS/CTS transactions are managed by MacLow

https://www.nsnam.org/docs/release/3.23/doxygen/classns3_1_1_mac_low.html#details

Regards

[Tom Henderson]

Please keep in mind that the below link is from the ns-3.23 release and
the Wi-Fi module has been significantly refactored since that time.
MacLow class has been removed as of the ns-3.33 release.

The

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[Soulimane Mammar]

Hi,

I have an ns-3.33 setup and the MacLow is still there, I checked 3.34 and indeed It has been removed.

When checking the depreciation list of 3.33, MacLow is not there!! 

I don't understand, I thought that before removing anything, it has to be marked as deprecated at least one version before

The whole Wifi module is driving me crazy, I'm trying to modify the behavior of the QoS adhoc MAC and It's been months that I'm trying to figure  out how things are related to each other

Nevertheless, Thanks for your update

Regards

[Soulimane Mammar]

Hi, 

I think that RTS/CTS exchange is now (versions  3.34 and higher) handled by the FrameExchangeManager

https://www.nsnam.org/doxygen/classns3_1_1_frame_exchange_manager.html

Regards