[ndnSIM] Question about ndnSIM for Data Freshness function.

Alex Afanasyev alexander.afanasyev at ucla.edu
Tue Dec 11 12:44:14 PST 2012

Dear Prasertsak,

Though it is possible to specify the freshness parameter in the ContentObject packet, ndnSIM does not yet have support for actually enforcing it.  Generally, as such a "cache" is just a temporary short-term buffer, it does not really matter.  You as a producer don't really have a control for how long routers would store your data, similarly how you don't have control for how long packets will be in routers interface queues.

Actually, Content Store name for the cache in ndnSIM is a little bit misleading, and we are planning to rename it to PacketBuffer in near future.

It should be pretty straightforward to add freshness functionality (similar how it is implemented in ndn-pit-impl.h/cc, but unfortunately I will be only available in a week or so to work on this.  


On Dec 11, 2012, at 5:55 AM, Prasertsak U. <gniliamg at gmail.com> wrote:

> Dear cawka (Alex Afanasyev),
> I'm Prasertsak from Thailand. I'm not a native speaker in English. I'd apologize if my English made you confuse.
> Now, I'm using the ndnSIM to simulate the CCN network in my research. However, I have a problem about "SetFreshness" function on the provider side. The data freshness seems to be not working, but I'm not sure because of the less experience about this tool.
> This is my simple environment for testing the data freshness:
> Consumer <------------> intermediate node <-----------------> provider
> I try to send the same prefix (i.e., "/data/10") to the provider and capture the interest packet at the provider node. Hence, the interest packet is replied by the provider application with freshness attributes. (Some parts of the code are shown below)
> ndn::ContentObjectHeader data;
> data.SetName (Create<ndn::NameComponents> (interest->GetName()));
> data.SetFreshness(Seconds(1.0));  
> data.SetTimestamp(Simulator::Now().GetSeconds()); 
> At the consumer side, the consumer application tries to send the same prefix (i.e., "/data/10") again, but the interest doesn't send through the provider after the second time. The response packet came from the cache only. In my opinion, the interest packet should send through the provider when the data in the cache is expired (by SetFreshness() function ... Is correct?).
> My question is 
> 	• Have the ndnSIM supported the data freshness?
> 	• How to use the data freshness of the ndnSIM? (If the data freshness had already supported.)
> Thank you very much.
> Regards,
> Prasertsak U.

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