Questions regarding the simulation evaluation

Asked by Nikola on 2009-04-09


I have a couple of questions regarding the evaluation of the simulation.

Firstly I give in the the offeredDL for our system. In my case I give 1e6 (ulIsActive = False). In the evaluation after that, i.e. wifimac.e2e.window.incoming.bitThroughput.hop_mean.m I get the value 1.002e+06, which is more that the offered load. In the simulation scenario I take one STA and one AP. Having channel capacity of 6 MBit/s there is no saturation.

I would like to know why do I get more throughput than I send.
Is the header size (IP and MAC) considered in the offered load or is it added additionally after that? What about the value in the evaluation? Is it with header or without? I saw that the MAC header used in openWNS has a size of 34 byte and the IP layer a size of 20 byte. There are additionally 22 bits preamble on the PHY layer. Are my considerations correct?

I tried to calculate the number of packets with fixed packet size of 1480 byte and then tried somehow to find where these additional 2 kbyte come from but with no success.

Does someone have an idea?

And another question.

I didn't find any description of the evaluation, i.e. what it exactly represents.

For instance the wifimac.e2e.packet.incoming.delay_dl_hc1_PDF.dat. What does this delay actually include? Sender's queue? Receiver's queue? Propagation delay? Any other delays? What exactly is being taken as incoming delay?

Is somewhere a description of this?

What about the wifimac.linkQuality.msduSuccessRate. How is it actually defined? Is just a 1 being added when a packet is received correctly and a 0 when dropped and then the whole sum normalized by the number of packets?
I searched in the simulator for the place where this is being calculated but couldn't find it.

Similar for the SINR. In wifimac.linkQuality.sinr_mean.m I get for example 48.9437 as SINR form the AP to the STA. How is this exactly being measured? At the station or at the receiver?

I again tried to locate the file where it is being calculated but couldn't find it.

It would be very helpful if some documentation could be provided regarding the already implemented evaluation output.

Thanks very much in advance.

Best regards,

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Harald Radke (rat-comnets) said : #1

Hello Nicola!

Regarding the mean probe values:

the traffic generator is above the IP FUN, so the 1.0e6 bit/sec traffic doesn't include IP nor MAC header overhead.

e.g. 1.0e6 bit/sec traffic with 8000 bit packet size -> 125 packets of traffic per sec
IP header size = 20*8 = 160 bit -> IP packet size = 8160 bit

125 * 8160 bit = 1,02e6 bit/sec

the wifimac.e2e probe is right at the top of the WIFIMAC, before the WIFIMAC overhead is added, so it reflects the IP packet size (MSDU). if you look at the wifimac.txUpper probe, which is below the wifimac overhead FU ( -> MPDU) it's value is even higher, adding WIFIMAC specific data to the above example it probes 1.054e6 bit/sec

1.054e6 - 1.02e6 = 34000 bit
34000 / 125 = 272 bit = 34 byte -> MAC header

any further mismatches might occur due to the fact that packets might not fall completly into probing windows

as a node, the ip.endToEnd.window probe should reflect the wifimac.e2e probe values since the IP probe measures packets with headers

Hope that helped a little bit


Harald Radke

Sebastian Max (smx-comnets) said : #2

Hi Nikola,

regarding your question concerning a description of the evaluation: No, there is currently no description of the different probes generated in the WiFiMAC (or in the other modules like IP, Constanze, etc).

A probe is always generated in a FU, but the name of the probe might not always indicate in which FU it is generated. Hence, without documentation, you have to grep through the source code (starting with the python files) for the prefix of the probe, e.g., wifimac.linkquality.

Then you can see where the probe is generated and look up in the FU code what exactly is put into the probe. If you would like to start a documentation about the probes in the WiFiMAC, I think that a 8th experiment in the users manual would be the perfect place for this. I would be willing to review this documentation, if you would like to publish it together with the openWNS.


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