[ndnSIM] Number of dropped packets

[Alex Afanasyev]

L2Tracer (there is no ndn namespace) shows number of packets dropped due to queue overflows.  In many cases of normal NDN communication, number of incoming interests is not equal to number of outgoing interests (same for data), as NDN router (in general) performing much more operations than just forwarding packets.

For example, if the same data piece is requested from two different neighbors, only the first interest will be forwarded, the second one will be either "collapsed" or satisfied from caches.   When Data packet comes, if there is no corresponding PIT entry (or entries), Data packet will be dropped (without L2Tracer knowing it).  If there is a PIT entry with multiple incoming faces (or multiple PIT entries), then more than one Data packet will be forwarded out.

At the same time, if you have a simple simulation where consumers requests unique pieces of content, then your formula should be correct, unless you're using forwarding strategy that enforces interest limits (e.g., PerOutFaceLimits).  How big is the number discrepancy?

---
Alex

On Mar 18, 2013, at 2:41 AM, Hovaidi Ardestani Mohammad <mohammad.hovaidi.ardestani at aalto.fi> wrote:

> Hello everybody!
> I am thinking that the following formula should give us the number of dropped packets.
> Number of Dropped packets = (Number of received interests + number of received data packets) - (Number of sent interests + number of sent data packets).
> If above formula is correct, then why on earth number of dropped packets shown by ndn::L2RateTracer is not equal with that?
> Thank you for your response in advance!
> -Mohammad
>  
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