[Ndn-interest] HopLimit=1 vs Interest aggregation

[Junxiao Shi]

Dear folks

I have a question on how to process an Interest with HopLimit=1 when the
Interest matches an existing PIT entry.

Topology:

A--\
    R---P
B--/

A and B are two downstream nodes. P and Q are two upstream nodes. All faces
are non-local.

Event sequence:

   1. R receives an Interest with HopLimit=32 from A, and forwards it to P.
   2. P is preparing a reply and not responding yet.
   3. R receives an Interest with HopLimit=1 from B.

Per v0.3 protocol:

if the HopLimit value is larger than or equal to 1, a node should accept
the packet and decrease the encoded value by 1.
If the HopLimit value becomes 0, a node can satisfy this Interest locally
(cache or applications bound to local faces), but must not forward the
Interests to any non-local faces.


R is prohibited from forwarding B's Interest to P. My question is: Does R
add B to the PIT entry as a downstream? Or should R respond Nack-NoRoute to
B?

My opinion is:
If B's Interest would arrive after P responds, it would have matched the
cached Data. Thus, R can add B to the PIT entry as a downstream, and send
the Data to B when it arrives.
However, B's Interest should not be considered as a consumer
retransmission, so the strategy should not attempt to resend A's Interest
to any non-local face.

Yours, Junxiao
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