[ndnSIM] Multicast Strategy , strange behavior

[Junxiao Shi]

Hi Ahmed

After an Interest is multicasted onto multiple paths but those paths join
at an upstream ("backbone" in the topology), the upstream would detect that
the Interests have duplicate Nonce and suppress all but the first Interest,
and send back the Data only along the path on which the Interest arrives
first.

Duplicate Nonce detection is done through the PIT entry and the Dead Nonce
List. See NFD Developer Guide "Forwarding - incoming Interest pipeline" and
"Tables - Dead Nonce List" sections for more information.
Detection through PIT entry is reliable: it can catch every incoming
Interest with duplicate Nonce and suppress it, as long as the PIT entry
still exists. A PIT entry stays for about 100ms after the Interest is
satisfied ("straggler timer"). When the three paths in the topology have
the same or almost same delay, it's almost guaranteed that the PIT entry
exists when the second and third Interest arrive, and thus they are
suppressed.

Detection through Dead Nonce List is selective: it's only used to prevent
"persistent loop" (NFD Bug 1953).
When the second and third paths have a delay that is more than 100ms longer
than the delay of the first path, the duplicate Nonce cannot be detected by
throug the PIT entry, and is usually not detected by the Dead Nonce List.
In this case, the Interest would be permitted to lookup the ContentStore,
find a match, and the cached Data is sent back.

Yours, Junxiao

On Thu, Mar 31, 2016 at 5:20 AM, Ahmed Sadek <don1559 at gmail.com> wrote:

> Hi All,
>
> I am using the following topology to try multicast strategy (broadcast).
> So I noticed that all requests are broadcasted but I am receiving only
> replies from one link (client->R3->Backbone).
>
>
>
>
> ​​
> When I increase the delay on one of the other two links during the
> simulation, I start receiving data replies on them also.
>
> I am assuming that on the intersection node (backbone) something stop data
> replication on the three interfaces and when there is a delay between
> interests this stop doesn't work.
>
> Can someone guide me, on what is happening here and why no data
> replication happening from the start ?
>
> Thanks!
> Ahmed
>
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>
>
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