[Ndn-interest] HopLimit=1 vs Interest aggregation
Teng Liang
philoliang at email.arizona.edu
Mon May 7 09:49:01 PDT 2018
On 5/7/18 8:00 AM, Junxiao Shi wrote:
> 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?
From my point of view, the HopLimit is just a mechanism to prevent an
Interest from being forwarded further than the expected. Therefore,
except the forwarding part, I don't see why a forwarder by default
should treat an Interest with HopLimit = 0 differently, so in your case
R will add B to the PIT entry as a downstream. You can always have
customized forwarding strategies for different behaviors.
Teng
>
> 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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