[Ndn-interest] Time and synchronization

[Marc.Mosko at parc.com]

The NDN spec for signed interests specifically says "Note that this verification process require signed interest to be received in order. Applications adopting this process may want to take 'stop-and-wait' strategy.”  Therefore, the actual synchronization of timestamps is not essential, they are just a non-monotonic increasing sequence number.  This may or may not work for you application.

Computing the grace interval, as specified there, does require at least loose synchronization of clocks.

> Note that for the first Interest, the state is not available. To handle this special situation, the recipient should check the Interest's timestamp against a grace interval (e.g., 120 seconds) [current_timestamp - interval/2, current_timestamp + interval/2]. The first interest is invalid if its timestamp is outside of the interval.


DTLS and IPsec use a sliding window, so they specifically protect against replay without enforcing ordered packet arrivals.  They use sequence numbers, not timestamps.

Marc

On Feb 5, 2015, at 1:05 PM, Chaim Rieger <chaim.rieger at gmail.com> wrote:

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> Followup
> After reading
> http://redmine.named-data.net/projects/ndn-cxx/wiki/SignedInterestProcessing
> 
> Snip...
> 
> valid signed Interest whose timestamp is equal or later than the
> timestamp of the received one has been received before.
> Note that in order to detect this situation, the recipient needs to
> maintain a latest timestamp state for each trusted public key
> 
> 
> This speaks to my question, NDN has some requirements that depend on
> Time/Timestamp. Who is the master of said Time ? If I were to generate
> data in the future (Time+60s) would that be read after data that is
> generated in RealTime 30 Seconds from now ?
> 
> 
> There seems to have been some minor discussion that broached this
> subject on this mailing list back in Sept of 2014.
> Does my question(s) make sense ?
> 
> 
> 
> On 2/5/2015 12:36 PM, Junxiao Shi wrote:
>> Hi Chaim
>> 
>> There isn't a timestamp on Data packet at network layer. If your 
>> application needs it, add a timestamp at application layer as part
>> of Content.
>> 
>> Yours, Junxiao On Feb 5, 2015 12:32 PM, "Chaim Rieger" 
>> <chaim.rieger at gmail.com> wrote:
>> 
>> When generating data that is for multicasting/distribution on an 
>> interactive level how would ndn keep track of the time across the 
>> network. Data has a requirement to be delivered and interacted
>> with at a certain time after which it should expire or be ignored.
>> Is there some sort of timekeeping within the NDN protocol ?
>>> _______________________________________________ Ndn-interest 
>>> mailing list Ndn-interest at lists.cs.ucla.edu 
>>> http://www.lists.cs.ucla.edu/mailman/listinfo/ndn-interest
>>> 
>> 
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