[Ndn-interest] any comments on naming convention?

[Marc.Mosko at parc.com]

I should clarify that the problems I describe below for selectors never knowing if there’s a more recent version apply to, I think, any protocol that’s talking with caches.  I don’t mean to pick on selectors, these arguments apply in general.  If the caches cannot tell you about the most recent, then you’ll never know by asking them.  So its not just selectors, it applies to exact match names or continuation names or any discovery method that gets responses from intermediate caches (unless there’s a consensus protocol operating, but then they are active participants not opportunistic caches).

Only a response from the producer — that says its from the producer and recent — could give an application assurance that its getting the really most recent version.   Distributed systems and consistency is a difficult problem.

Marc

On Sep 25, 2014, at 11:09 PM, <Marc.Mosko at parc.com> <Marc.Mosko at parc.com> wrote:

> 
> On Sep 25, 2014, at 10:01 PM, Lan Wang (lanwang) <lanwang at memphis.edu> wrote:
> 
>>>> - Benefit seems apparent in multi-consumer scenarios, even without sync.
>>>> Let's say I have 5 personal devices requesting mail. In Scheme B, every
>>>> publisher receives and processes 5 interests per second on average.  In
>>>> Scheme A, with an upstream caching node, each receives 1 per second
>>>> maximum. The publisher  still has to throttle requests, but with no help
>>>> or scaling support from the network.
>>> 
>>> This can be done without selectors.  As long as all the clients produce a
>>> request for the same name they can take advantage caching.
>> 
>> What Jeff responded to is that scheme B requires a freshness of 0 for the initial interest to get to the producer (in order to get the latest list of email names).  If freshness is 0, then there's no caching of the data.  No meter how the clients name their Interests, they can't take advantage of caching.
>> 
> 
> How do selectors prevent you from sending an Interest to the producer, if it’s connected.  I send first interest “exclude <= 100” and cache A responds with version 110.  Don’t you then turn around and send a second interest “exclude <= 110” to see if another cache has a more recent version?  Won’t that interest go to the producer, if its connected?  It will then need to send a NACk (or you need to timeout), if there’s nothing more recent.
> 
> Using selectors, you still never know if there’s a more recent version until you get to the producer or you timeout.  You always need to keep asking and asking.  Also, there’s nothing special about the content object from the producer, so you still don’t necessarily believe that its the most recent, and you’ll then ask again.  Sure, an application could just accept the 1st or 2nd content object it gets back, but it never really knows.  Sure, if the CreateTime (I think you call it Timestamp in NDN, if you still have it) is very recent and you assume synchronized clocks, then you might have some belief that it’s current.
> 
> We could also talk about FreshnessSeconds and MustBeFresh, but that would be best to start its own thread on.
> 
> Marc
> 
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