help regarding DropTail queue behavior

Hello,

I am a ns-3 user and have a question regarding the behavior of a drop-tail
queue. I had initially posted my question on ns-3 users google group but
could not find help.

The post could be accessed at
https://groups.google.com/forum/?fromgroups#!topic/ns-3-users/-MKEEtpwQck I
have also added the details of my issue at the end of this mail.

Any help in this regard would be greatly appreciated.

Cheers,
Siddharth
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Siddharth Gangadhar
Graduate Research Assistant
217 Nichols Hall, Information Technology and Telecommunications
Center<http://www.ittc.ku.edu/>
siddharth@{ittc}.ku.edu, www.ittc.ku.edu/~siddharth
The University of Kansas <http://www.ku.edu/>
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----------------------------------------------------
"""
Hello,

I am currently working on simulating a congestion scenario at a router with
a drop tail queue. The arrival rate of packets at the router is much higher
than the service rate (bottleneck link) and I use a finite buffer. I see
that there are not many packet drops that I would see theoretically in the
network. The details are given below:

I consider a source and a sink connected through a couple of gateways in
between. The bottleneck link is the gateway-gateway link.  Congestion is
being simulated at the gateway connected to the source or in other words
the first hop from the source. I understand that this is a heavily
congested network but I was just testing the check if all functionalities
were working ok.

Simulation Parameters and configuration
source----gateway----gateway-----sink
Arrival Rate (source-->gateway) = 10 KBps
bottleneck link rate (gateway-->gateway) = 5 KBps
Buffer Size = 10 B

The buffer size was set at the gateways using the MaxBytes mode given below
UnReLink.SetQueue ("ns3::DropTailQueue",
       "Mode", StringValue ("Bytes"),
       "MaxBytes", UintegerValue (10));

The total packet drops I could see for this case was 7. I tried changing
the queue sizes but still only a very small fraction of the theoretical
packet drops could be seen and nowhere near the huge packet drops I would
expect theoretically. The packet drops were noted by logging the
DropTailQueue class and looking for the packet drop log. Another
interesting part I saw in the logging was the queue was holding more
packets than I asked it to. Am I doing something wrong  or missing
something here?

Thanks,
Siddharth
"""