[ndnSIM] Packet drops

[Alex Afanasyev]

Hi Yusung,

Yes. Normally drops are due to transmission queue overflow at layer 2.  The "trace source" path "/NodeList/*/DeviceList/*/TxQueue/Drop" is saying that we are selecting all simulation nodes (/NodeList/*), all network devices on each node (DeviceList/*), from each netdevice we are accessing TxQueue, in where we are connecting to Drop trace source.   You may want to check NS-3 documentation about trace sources and connecting to them.

NS-3 does not implement concept of dropping on input and there are no input interface queues.  Time to handle packet is relevant in a real system, in NS-3, unless you specifically design processing to emulate real process, it is assumed that any method takes exactly 0s of simulation time.  

In NDN, a forwarding strategy may decide to drop Interest if it thinks that there is a congestion in the reverse path.  This is not real congestion, but NDN-specific drop.  If you want, you can check out our paper (http://dx.doi.org/10.1016/j.comcom.2013.01.005, http://lasr.cs.ucla.edu/afanasyev/data/files/Yi/comcom-stateful-forwarding.pdf) where we designed a rough prototype for such strategy.

---
Alex

On Feb 27, 2013, at 5:53 PM, Yusung Kim <yskim525 at gmail.com> wrote:

> Hello Mohammad  and Alex, 
> 
> May I ask you more scenarios in which congestion happens in NDN ? 
> 
> One example,  Alex said,  is drops due to queue overflows.
> Is the transmission queue at Layer2 , right ?
> ( To Alex,  what is the default queue size ? )
> 
> Is it possible that packets are dropped at an  input interface queue ?
> For example,  When lots of packets arrived from multiple input interfaces,
> if the time to handle the packets ( name look-up, cache replacement.. ) increases, 
> new incoming packets may be dropped at input interface queues ?
> 
> If you know another scenarios about packet drops, would you let me know the scenarios?
> Thank you,
> 
> - Yusung Kim -
> 
> 
> 
> On Thu, Feb 28, 2013 at 5:27 AM, Alex Afanasyev <alexander.afanasyev at ucla.edu> wrote:
> Hi Mohammad,
> 
> If you're talking about normal drops due to queue overflows, then you can use packet drop traces from NetDevice queue (you can check examples in src/visualizer/model/pyviz.cc):
> 
> - /NodeList/*/DeviceList/*/TxQueue/Drop
> 
> If you want to factor in cases when ndnSIM stops forwarding packet (which is not exactly a drop), then you may want to also use
> 
> - /NodeList/*/$ns3::ndn::ForwardingStrategy/DropInterests
> - /NodeList/*/$ns3::ndn::ForwardingStrategy/DropData
> 
> However, I'm not confident 100% that right now ndnSIM tracks all the cases of stopped forwarding of Interst/Data.
> 
> ---
> Alex
> 
> On Feb 27, 2013, at 5:51 AM, Hovaidi Ardestani Mohammad <mohammad.hovaidi.ardestani at aalto.fi> wrote:
> 
> > Hello everybody!
> > I have several scenarios in which congestion happens. I am wondering how I can trace dropped packets or know when packet dropping has been started?
> > Any help is appreciated in advance
> > BR
> > -Mohammad
> 
> _______________________________________________
> ndnSIM mailing list
> ndnSIM at lists.cs.ucla.edu
> http://www.lists.cs.ucla.edu/mailman/listinfo/ndnsim
> 
> _______________________________________________
> ndnSIM mailing list
> ndnSIM at lists.cs.ucla.edu
> http://www.lists.cs.ucla.edu/mailman/listinfo/ndnsim

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.lists.cs.ucla.edu/pipermail/ndnsim/attachments/20130228/ba98ee3c/attachment.html>