[ndnSIM] Question on FIB matching

[Alex Afanasyev]

Hi Asit,

I'm thinking to remove a requirement to have a valid FIB entry, in order to attempt to process interests (though I will still PIT creation procedure), but don't yet have a time frame for that.

You can add default routes automatically using ndn::StackHelper::SetDefaultRoutes method http://ndnsim.net/doxygen/classns3_1_1ndn_1_1_stack_helper.html#a12b1c8f16bad953ac3b9bb4a6ab1fcab.  If you don't want to have a dummy prefixes in FIB, you can try to remove lines 350-352 in model/pit/ndn-pit-impl.h, but you probably would need to check other parts of the code, since it was assumed that PIT entry has always a valid reference to PIT: A FIB entry is basically a place where information about past performance of Interest/Data exchanges within this prefix can be stored. 

---
Alex 

On May 8, 2013, at 5:08 PM, Asit Chakraborti <Asit.sc.Chakraborti at huawei.com> wrote:

> Hi Alex,
>  
> Thanks for the response, that makes sense. I needed to process the interests differently and was planning to create a new
> Forwarding strategy, however, the interests got dropped and didn’t get delivered to the new strategy as there was no
> FIB match. Either I have to modify the common code to allow PIT entries with no matching FIB (not sure how badly that
> would violate the entire model), or may be I will try to have dummy “/” entries in the FIB…
>  
> Thanks,
> Asit.  
>  
> From: Alexander Afanasyev [mailto:cawka1 at gmail.com] On Behalf Of Alex Afanasyev
> Sent: Wednesday, May 08, 2013 4:28 PM
> To: Asit Chakraborti
> Cc: ndnsim at lists.cs.ucla.edu
> Subject: Re: [ndnSIM] Question on FIB matching
>  
> Hi Asit,
>  
> The currently implemented way always attempts to lookup FIB and create PIT entry for incoming interest, and if there is a CS match, such a PIT entry will be immediately satisfied.
>  
> The main reason behind this implementation is to unify metric calculation: for every interest there will always be either new or existing PIT entry, and every satisfied interest can be tracked via PIT entry satisfaction.  It is technically  possible to change the implementation, but I'm not yet sure if this would get any major benefits.
>  
> As for last question.  Yes, it is assumed that there is always some FIB entry, at least a default entry for root prefix, that can match incoming interests.  And if there is no such entry, then NDN router is not willing to do anything with such interests.
>  
> Do you have a specific scenario where this assumption doesn't hold?  It is relatively easy to create an alternative forwarding strategy with slightly different processing logic.
>  
> ---
> Alex
>  
> On May 8, 2013, at 3:31 PM, Asit Chakraborti <Asit.sc.Chakraborti at huawei.com> wrote:
> 
> 
> Hi Alex,
>  
> My understanding of the code could be wrong, but it seems we require a FIB match on an incoming
> Interest even before a CS match. Any historical reason behind this ? Or is it just the fact that with
> the current model and APIs, a FIB entry usually exists if the content is in content store ?
>  
> Thanks,
> Asit.
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