p2psp team mailing list archive

[Cristóbal Medina López <cristobalmedinalopez@xxxxxxxxx>]

Hi Ilshat,

We think that the formula is fine. Only one question (see bellow):

El lun., 30 de marzo de 2015 a las 14:58, Ilshat Shakirov (<
im.shakirov@xxxxxxxxx>) escribió:

> Hello!,
>
> I got a new results from experiments with new parameters (2 trusted and
> one attacker), and it doesn't match with expected results from
> http://p2psp.org/en/p2psp-protocol?cap=indexsu11.xht#x20-160004.11
> (formula 11)
> But I deduced new formula (only for these params for now (T=2, A=1)):
>
> ​
> , where n is team size.
> ​Let me explain it:
> It just a formula for expected value for discrete random variable. So let
> describe our discrete variable:
> We have n peers, 2 trusted peers and one attacker. Size of each node's
> peer list is* n - 1*. Number of possible permutations for 2 trusted peers
> in attacker's peer list is *N = (n - 1) * (n - 2) / 2.*
>

Could you explain at length the previous formula? (anyway we think that it
also works perfectly)


>
> The probability for getting only one poisoned chunk in the netowrk is *P(1)
> = (n - 2) / N*; (because we're getting only one poisoned chunk when
> trusted peer is the first in attacker's peer list, so there is n-2 variants
> of this situation).
> Next, *P(2) = (n - 3) / N*, P(x) =* (n - x - 1) / N*
> The max possible number of poisoned chunks in network with 2 trusted peer
> and one attacker is n - 2 (n - attacker - trusted);
> So, we must only to compute expected value as sum of *P(x)*x*.
>
> Formula can be easily generalized to different numbers of attackers and
> trusted peers, but first I want to know your opinion about it.
> What do you think? =)
> <https://en.wikipedia.org/wiki/Discrete_random_variable>
>
>
Please, check that the following python code implements your formula:

x = 0.0
n = 10
for i in range(1,n-2):
    y=2.0*i*(n-i-1)/((n-1)*(n-2))
    print y, i
    x+=y
print x

Thanks,
Regards.



>
> 2015-03-29 1:43 GMT+05:00 Ilshat Shakirov <im.shakirov@xxxxxxxxx>:
>
>> Hello!,
>>
>> Sorry for the delay in the response.
>> I have just improved the Peersim impl of P2PSP:
>> - malicious peer connects to the team after some delay (magic constant :))
>> - *CHUNK *message have 4 times more delay than other messages (hello,
>> goodbye, etc.)
>> - trusted and malicious peers are chosen randomly at the begin of
>> simulation
>>
>> I have performed new experiments with these improvements, it can be
>> accessed at the same doc -
>> https://docs.google.com/spreadsheets/d/1pc6yb87xJy8gNkWSWvvCvjAjR6WBFdOzCbPvO-zEooU/edit#gid=0
>> - it has 2 new tabs - raw2 and result2.
>> *raw2 *tab have 2 sets of data - the first one was performed without
>> different latencies, and the second one was performed with different
>> latencies.
>> Could you please evaluate results? What the next steps you want to see
>> with peersim impl of p2psp? =) I want to perform experiments with different
>> numbers of trusted peers and attackers, in order to confirm theroretical
>> analysis given in paper.
>>
>> Also, I want to store all the logs from each experiment in the same
>> place. I want to use dropbox for this (shared dir). What do you think? =)
>>
>> Currently, Im preparing scripts (bash and bat) to run simulation, so
>> there will be possible to perform experiments without setting up IDE.
>>
>> ps Could you please include me to sim project on github? Or we will work
>> with pull requests? =)
>>
>> Thanks in advance!
>>
>>
>> 2015-03-20 18:48 GMT+06:00 Vicente Gonzalez <
>> vicente.gonzalez.ruiz@xxxxxxxxx>:
>>
>>>
>>>
>>> 2015-03-20 9:59 GMT+01:00 Ilshat Shakirov <im.shakirov@xxxxxxxxx>:
>>>
>>> I don't know the procedure you are using to add peers to a team (how the
>>>>> peers contact the splitter, receives the list of peers of the splitter and
>>>>> send the [hello] message to the peers that are in the list), but I suppose
>>>>> that this procedure is similar to one used in a real team.
>>>>
>>>> Yes, the peers are added to team as it described in DBS of rules (new
>>>> peer sends HELLO to splitter, splitter sends list of peers, peer sends
>>>> HELLO to rest of team).
>>>>
>>>
>>> OK.
>>>
>>>
>>>> I have new hypothesis - how much time is spent for sending chunks? and
>>>> for sending simple messages, like HELLO/GOODBYE. In peersim implementation
>>>> there is no difference in times between these two types of message. If it's
>>>> able to send 2 or more simple messages while one chunk is sending, then
>>>> simulation results will match with expected results.
>>>>
>>>
>>> When a peer is introducing himself to the rest of the team only sends
>>> [hello]s. To interlace [hello]s and chunks, the splitter should send first
>>> to it a chunk, and this is done after receiving the list of peers from the
>>> splitter. This does not happen.
>>>
>>> In my opinion, a better result (not only for this experiment) could be
>>> obtained if you assign a latency to each message that depends on the
>>> message's length.
>>>
>>>
>>>> This means that if the peer 34 were the trusted peer, the attacker
>>>>> would send only one poisoned chunk before it is reported. For this reason,
>>>>> I think that the order of the peers in the lists should have some influence
>>>>> in the average number of poisoned chunks.
>>>>
>>>> There is such results already. I.e. cell D43 in google sheet
>>>> <https://docs.google.com/spreadsheets/d/1pc6yb87xJy8gNkWSWvvCvjAjR6WBFdOzCbPvO-zEooU/edit#gid=0>.
>>>>
>>>>
>>>
>>> I see :-)
>>>
>>>
>>>>
>>>> Also, I can remove the latency for simple messages (like hello and
>>>> goodbye), and (I suppose) results will match with expected results.
>>>>
>>>
>>> No. Please, consider first my idea (longer messages will take more time
>>> traveling that shorter ones).  And, randomize, if possible, the order (or
>>> time) in which peers join the team.
>>>
>>>
>>>>
>>>> An accurate P2PSP simulator is very interesting for researching the
>>>>> performance of the P2PSP. Any kind of advance/facility in this direction is
>>>>> really appreciated :-)
>>>>
>>>>
>>>
>>>> Ok, I will begin to write readme file about performing experiments =)
>>>>
>>>
>>> Again, thanks. Your work will be very helpful!!
>>>
>>> Best,
>>> Vi.
>>>
>>> --
>>> Vicente González Ruiz
>>> Depto de Informática
>>> Escuela Técnica Superior de Ingeniería
>>> Universidad de Almería
>>>
>>> Carretera Sacramento S/N
>>> 04120, La Cañada de San Urbano
>>> Almería, España
>>>
>>> e-mail: vruiz@xxxxxx
>>> http://www.ual.es/~vruiz
>>> tel: +34 950 015711
>>> fax: +34 950 015486
>>>
>>
>>
>

x = 0.0
n = 10
for i in range(1,n-2):
    y=2.0*i*(n-i-1)/((n-1)*(n-2))
    print y, i
    x+=y
print x