[ndnSIM] Inconsistency of Random replacement policy

Saran Tarnoi sarantarnoi at gmail.com
Fri Jun 7 04:52:16 PDT 2013

Dear Saeid and All,

Thank you very much for your helpful answer. :)
I also agree with your first thought. Two nodes may use the same generated
sequence of random seed.

In my experiment, the number of generated interests was quite small,
200,000 interests with 60,000 interest warm up period.
The cache size is 100 objects.
The scale is tiny but the difference of results obviously appears.

I'm running simulation for 2,000,000 interests with 1,000,000 interest warm
up period to see whether or not the interest number can help.
Thank you again.

Saran Tarnoi

2013/6/7 Saeid Montazeri <saeid.montazeri at gmail.com>

> 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
>> _______________________________________________
>> ndnSIM mailing list
>> ndnSIM at lists.cs.ucla.edu
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Saran Tarnoi
Graduate Student
Department of Informatics
The Graduate University for Advanced Studies (Sokendai)
Tokyo, Japan
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