Discussion:
Calculating Propagation delay on NS-3
Mallesh Yadhav
2015-08-28 09:53:21 UTC
Permalink
Hi,

I am able calculate the transmission delay but not propagation
delay on ns3. Is there any way to calculate the same at the MAC layer.

Thanks & regards,
Mallesh
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Konstantinos
2015-08-28 10:02:33 UTC
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Hi,

Signals propagate with the speed of light, so the propagation delay for
WiFi is in the order of 1-2us (common values used in the the literature).
Note also that if you use FlowMonitor (that you have as tag in your post),
it accounts for both propagation and transmission delay as it is End-to-End
at IP layer.

Regards,
K
Post by Mallesh Yadhav
Hi,
I am able calculate the transmission delay but not propagation
delay on ns3. Is there any way to calculate the same at the MAC layer.
Thanks & regards,
Mallesh
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Mallesh Yadhav
2015-08-28 10:10:09 UTC
Permalink
Thank you very much for the quick response.

In ns3, there are two propagation models: constant and random
propagation models. I want to know the propagation delay of packets under
mobile scenarios with random propagation model.

Is it possible? Or as you said, is not worth calculate the
propagation delay as the order is of single digit micro seconds.
Post by Konstantinos
Hi,
Signals propagate with the speed of light, so the propagation delay for
WiFi is in the order of 1-2us (common values used in the the literature).
Note also that if you use FlowMonitor (that you have as tag in your post),
it accounts for both propagation and transmission delay as it is End-to-End
at IP layer.
Regards,
K
Post by Mallesh Yadhav
Hi,
I am able calculate the transmission delay but not propagation
delay on ns3. Is there any way to calculate the same at the MAC layer.
Thanks & regards,
Mallesh
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Konstantinos
2015-08-28 10:21:30 UTC
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It will depend on the random variable you use.
If you check the source code for RandomPropagationDelay

76 Time <https://www.nsnam.org/docs/doxygen/classns3_1_1_time.html>
77
<https://www.nsnam.org/docs/doxygen/classns3_1_1_random_propagation_delay_model.html#a34e6b680eb47894f3a40d765ed1ed1bf>
RandomPropagationDelayModel::GetDelay
<https://www.nsnam.org/docs/doxygen/classns3_1_1_random_propagation_delay_model.html#a34e6b680eb47894f3a40d765ed1ed1bf>
(Ptr<MobilityModel>
<https://www.nsnam.org/docs/doxygen/classns3_1_1_ptr.html> a,
Ptr<MobilityModel>
<https://www.nsnam.org/docs/doxygen/classns3_1_1_ptr.html> b) const
78 {
79 return Seconds
<https://www.nsnam.org/docs/doxygen/group__timecivil.html#ga33c34b816f8ff6628e33d5c8e9713b9e>
(m_variable
<https://www.nsnam.org/docs/doxygen/classns3_1_1_random_propagation_delay_model.html#a1f026b6a646d862d0eca4ba3906cd8a2>
->GetValue
<https://www.nsnam.org/docs/doxygen/classns3_1_1_random_variable_stream.html#a4fa5944dc4cb11544e661ed23072b36c>
());
80 }

The delay does not relate to the position of the nodes, but it comes from
the random variable you use; by default Uniform from (0,1)seconds.
So, if you keep the default configuration, you should NOT discard it, but
it is not realistic for simple WiFi at those ranges.

But if you want my advice, I would use the ConstantSpeedDelay that takes
into account the distance of the nodes.
Post by Mallesh Yadhav
Thank you very much for the quick response.
In ns3, there are two propagation models: constant and random
propagation models. I want to know the propagation delay of packets under
mobile scenarios with random propagation model.
Is it possible? Or as you said, is not worth calculate the
propagation delay as the order is of single digit micro seconds.
Post by Konstantinos
Hi,
Signals propagate with the speed of light, so the propagation delay for
WiFi is in the order of 1-2us (common values used in the the literature).
Note also that if you use FlowMonitor (that you have as tag in your
post), it accounts for both propagation and transmission delay as it is
End-to-End at IP layer.
Regards,
K
Post by Mallesh Yadhav
Hi,
I am able calculate the transmission delay but not propagation
delay on ns3. Is there any way to calculate the same at the MAC layer.
Thanks & regards,
Mallesh
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Tommaso Pecorella
2015-08-28 10:25:22 UTC
Permalink
Hi,

the RandomPropagationDelayModel (please use the full name to avoid
confusion) is mainly used in tests and it doesn't represent anything
realistic. I mean... under this model the propagation delay between every
node pair is totally random - by default between 0 and 1 second. But wait,
there's more. It's not only random between each pair of nodes, it's
different for each packet sent !
Basically... useful only to stress test stuff.

Have fun,

T.
Post by Mallesh Yadhav
Thank you very much for the quick response.
In ns3, there are two propagation models: constant and random
propagation models. I want to know the propagation delay of packets under
mobile scenarios with random propagation model.
Is it possible? Or as you said, is not worth calculate the
propagation delay as the order is of single digit micro seconds.
Post by Konstantinos
Hi,
Signals propagate with the speed of light, so the propagation delay for
WiFi is in the order of 1-2us (common values used in the the literature).
Note also that if you use FlowMonitor (that you have as tag in your
post), it accounts for both propagation and transmission delay as it is
End-to-End at IP layer.
Regards,
K
Post by Mallesh Yadhav
Hi,
I am able calculate the transmission delay but not propagation
delay on ns3. Is there any way to calculate the same at the MAC layer.
Thanks & regards,
Mallesh
--
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