[ndnSIM] NACKs in ndnSIM2.0?

Lixia Zhang lixia at CS.UCLA.EDU
Sun Feb 8 12:12:00 PST 2015

> On Feb 8, 2015, at 10:47 AM, Christian Kreuzberger <christian.kreuzberger at itec.aau.at> wrote:
> Hi,
> I have a follow-up question about NACKs in NFD/ndnSIM:
> are there ongoing discussions or RFCs about how NACKs should be used and/or
> interpreted? http://named-data.net/doc/ndn-tlv/data.html states that NACK has
> been removed on purpose, but: "NACK is used to signal a downstream node that
> the upstream node is unable to retrieve a matching data. Since the actual NACK
> mechanism is still under active investigation, we do not include it in this
> version of specification, but may add it back in a future version".
> Best regards,
> Christian

ndnSIM 2.0 tried to reflect the real NFD and cxx code, hence the absence of a NACK (that was in 1.0).  But yes there are ongoing efforts about NACK.  The current thinking leads to more than one type of NACK.
1/ What you quoted above is an upstream-to-downstream notification due to problem in further forwarding an Interest packet, so that the downstream node may act ASAP (e.g. explore alternative path).

2/ There is also a need for application NACK, for the origin producer to inform consumers about data unavailability. 

the NACK in either case should carry additional info about the cause, so that the receiver of a NACK can properly interpret/handle it.

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