[Nfd-dev] Broadcast suppression in Self Learning Forwarding Strategy

[Junxiao Shi]

Hi Mahyuddin


> During flooding (discovery and announcement), is there any specific
> broadcast suppression technique applied?
>
The only suppression is Interest aggregation that aggregates multiple
Interests with same name, selectors, and forwarding hint.

If more than one consumer doing content discovery (interest packet flooding)
>
Interest aggregation is effective for this, if the consumers are sending
Interests with same name, selectors, and forwarding hint. It cannot help if
the consumers are asking for different content.


> or more than one producer doing content name prefix announcement (data
> packet flooding) using blind flooding
>
This does not happen in self-learning. Producer cannot flood Data packets
without first receiving an Interest.


> it will lead to flooding overhead and probably lead to broadcast storm (
> https://en.wikipedia.org/wiki/Broadcast_radiation) on the local network.
>
Yes, if the Interests are asking for different content, and they are all
sent before the path is learned.


Teng's answer:

> For the self-learning, only the first Interest will be flooded; subsequent
> Interests and Data packets are sent along a single path. If a flooded
> Interest reaches a node that has a matching FIB entry, the flooded Interest
> will not be flooded anymore. If multiple consumers send Interests with the
> same name, NFD will do Interest aggregation instead of sending redundant
> Interests out (this is a generic mechanism, not self-learning specific).
> Thus the self-learning will not lead to broadcast storm, but to avoid it.
>
This answer is correct. Broadcast storm does not occur if (1) flooded
Interests have same name, selectors, and forwarding hint; or, (2) flooded
Interests do not arrive at the same time, in which case only the first few
would be flooded, and others are quickly converted into non-discovery
unicast Interests as soon as they hit a node that knows the path.
However, this answer fails to point out that: broadcast storm could occur
if multiple consumers, at the same time, are flooding Interests with
different name, selectors, or forwarding hint.

Yours, Junxiao
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