[Nfd-dev] ncc strategy

[Syed Obaid Amin]

On Wed, Sep 10, 2014 at 1:24 PM, Junxiao Shi <shijunxiao at email.arizona.edu>
wrote:

> Hi Lan
>
> The fix for Bug 1961 improve the results because it ensures an upstream
> who isn't first to respond won't be incorrectly recorded as best face.
>
> The patched figure shows two links are used. ARIZONA-CSU-CAIDA has RTT
> 72ms; ARIZONA-MEMPHIS-CAIDA has RTT 156ms.
> CSU node fails at message 60, and recovers at message 180.
> The experiment ends at message 300.
>
> *NCC strategy fails to switch back to CSU after its recovery. This is
> either a weakness of ccnd strategy, or a misunderstand when it's ported to
> NFD.* This is not an experiment problem, and cannot be solved by running
> experiment for longer time.
> Detail analysis follows.
>
> NCC strategy maintains an RTT prediction for the best face of each Name
> prefix. The granularity is at Interest Name minus the last component
> (usually a segment number).
>
>    - RTT prediction starts at 8.192ms.
>    - If Data comes within prediction, prediction is adjusted down by
>    1/128, and minimum is 0.127ms.
>    - If Data doesn't come within prediction, prediction is adjusted up by
>    1/8, and maximum is 160ms.
>    - The effect of above two point is: ultimately, prediction oscillates
>    around real RTT (if real RTT is between 0.127ms and 160ms).
>    - If Data doesn't come within prediction, other faces will be tried,
>    starting from the end of original prediction.
>    The previous best face, along with one other face who has lowest
>    routing cost, are tried first.
>    Other faces are tried one by one, in a short period of time.
>
> Two important points are:
>
>    - All except the best face are propagated to, after the prediction.
>    This means, the Interest is forwarded to CSU 154ms (=156*127/128) later
>    than forwarding to MEMPHIS.
>    - Incoming face of the first Data that satisfies the Interest becomes
>    the best face. If the MEMPHIS link does not fail, the Data would always
>    arrive first, because the Interest is forwarded 154ms earlier. Therefore, *CSU
>    link can never become the best face, unless MEMPHIS link fails, or until
>    the traffic stops so that measurements are wiped out*. This is
>    confirmed by my calculation in Excel.
>
> Questions:
>
>    - Does the routing protocol uninstall and re-install the Route during
>    this experiment? If yes, please give the time point at which the FIB update
>    is applied (a time point shall be given as "just before sending Interest
>    for message X" so that I can correlate to messages).
>
> Not sure what do you mean here. At 60th sec, the CSU node was brought
down, as a result all other nodes update their routing tables. But we don't
have any timestamps as the logging was not on.


>
>    - If you have results of a similar experiment with ccnd or ndnd,
>    please share them, so that I can confirm whether it's a design weakness or
>    implementation bug.
>
> I've data from ccnx, but that experiment ran for 180 secs only. I am
attaching here the file. If seems useful I can re-run the experiments with
ccnx. But it may take little time for exact setup.

 Regards,
Obaid


>
>    -
>
>
> Yours, Junxiao
>
> On Wed, Sep 10, 2014 at 9:17 AM, Lan Wang (lanwang) <lanwang at memphis.edu>
> wrote:
>
>>  Can you give a detailed explanation of the observed behavior and how/why
>> the patch improved the results?
>>
>>  Also why didn't Arizona switch back to the faster path when CSU came
>> back?
>>
>>  Lan
>>  On Sep 10, 2014, at 11:09 AM, Syed Obaid Amin <obaidasyed at gmail.com>
>>  wrote:
>>
>>  Hi Junxiao,
>>
>>  Thanks for the fix. The patch improved the results significantly. For
>> e.g., have a look at the following results:
>>
>>  Old strategy:
>>
>> http://netwisdom.cs.memphis.edu/hr_evaluation/tests-withfailure-oldncc_nolog/arizona-caida-converge.png
>>
>>  Patched:
>>
>> http://netwisdom.cs.memphis.edu/hr_evaluation/tests-withfailure-ncc_nolog/arizona-caida-converge.png
>>
>>  The topology I used for these tests can be found here:
>> http://netwisdom.cs.memphis.edu/imgs/topology.png
>>
>>  Regards,
>> Obaid
>>
>>
>
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