[ndnSIM] Inconsistency of Random replacement policy

[Saeid Montazeri]

Dear Saran,

Would you please let us more about your experiment setting: how long the
consumer generates Interests or how many requests are generated?

Meanwhile, my guess is that the problem may be because of the sequence of
the random number that is used by random replacement policies. *If both
policies in node 1 and 2 use the same random number generator(or at least
dependent random number generators)*, the problem is because of that. If we
assume that is the case, suppose that a random number sequences for cache
size equals 2 be 1,2,1,2,2,1. (3 means that incoming Data packet will not
be written to the cache). If only one replacement policy is random
then 1,2,3,1,3,2,2,1 will be the replaced slots in the first node. However,
if both of the nodes have random replacement policies, the replaced slot in
the first node depends on the misses in the second node. *If the policies
in node 1 and 2 use independent random generators*, I have no idea.
In any case, would you please let us know for how many requests you did the
experiment. Because I think it should be related to the
transient behavior of the system and if you run the simulation for enough
long period of time, you may get pretty close results.

Best Regards,
Saeid



On Fri, Jun 7, 2013 at 4:19 PM, Saran Tarnoi <sarantarnoi at gmail.com> wrote:

> Hello Alex and All,
>
> I did some experiments and found some wired results.
> The experimental setup is as follows.
>
> (Random, Lru, or Lfu)   node 2 <--- (producer)
>                                      l
>                                      l
>         (Random)            node 1 <--- (consumer, Zipfmandelbrot)
>
> The cascading network has 2 nodes.
> These nodes has the same size of Content Store.
> Consumer and producer are installed in nodes 1 and 2, respectively.
> Zipfmendelbrot is set as the Interest traffic model for consumer.
>
> Random is the replacement policy for node 1 while either Random, Lru, or
> Lfu is the replacement policy of node 2.
>
> The cache hit rate at node 1 (the first-hop node) should be consistent and
> independent of the replacement policy deployed in node 2.
> However, the results don't follow the above logic.
>
> The cache hit rate at node 1 when either Lru or Lfu is set as the
> replacement policy of node 2 are exactly the same but different from when
> Random is the replacement policy of node 2.
>
> In addition, I don't see any problem when Lfu or Lru is set as replacement
> policy of node 1.
>
> Is it a bug or random seed problem?
> Could you give me any idea?
> Thanks a lot for your time.
>
> Regards,
> Saran Tarnoi
>
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