[Ndn-interest] Routing and forwarding in NDN

[Klaus Schneider]

I think there's two questions here:

1. What is currently done?

That depends on the specific forwarding strategy which is used. You can 
find a summary of their functions in the NFD Developer Guide: 
https://named-data.net/wp-content/uploads/2018/07/ndn-0021-10-nfd-developer-guide.pdf

For example, the "Best Route Strategy" will do nothing about the lost 
Interest, but wait for a consumer retransmission. If the consumer 
retransmits, the new Interest will go to the second best face, i.e., node 4.


2. What can be done / what should be done?

You already identified a number of reasonable suggestions: 
retransmitting on the same/different face, or flooding the Interest. 
Some questions to ask:

- Flooding is quite expensive. How to prevent the network from being 
overloaded by flooding every lost Interest?

- What timeout to use before retransmitting at each router? What happens 
if multiple routers on the path retransmit the same lost Interest at 
roughly the same time? (it becomes more like flooding the network)

- Should a router suppress a previously seen Interest if it has recently 
sent out this Interest and is waiting for an answer? If yes, how long?

- Should a router remember that one if its faces cannot provide data? If 
yes, after which threshold (is one lost Interest enough)? And with which 
granularity (per-object, per-prefix)? How does a router know when a face 
will be able to provide data again (assuming the problem is more than 
one hop away)?

The answers to these questions depend on your topology and your 
scenario. E.g. you probably want a different forwarding strategy for 
wireless ad-hoc networks than for wired backbone networks.


Best regards,
Klaus



On 11/13/18 11:09 PM, Tanusree Chatterjee wrote:
> Hello all,
> 
> Please tell me, if an interest is not served by any data, the interest 
> is discarded, next the interest is flooded in the entire network to find 
> the corresponding data? Up to what time it should wait before flooding?
> 
> Again, if an interest can be served by 3 nodes, say node1, node4 and 
> node6. Now, after searching the FIB, the interest is forwarded to node1. 
> But,due to some problems, data has not arrived back. What is done next? 
> Retransmission of the same interest, flooding of the interest or 
> forwarding the interest to node4?
> 
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