[Nfd-dev] Fwd: Redundant data transmissions on error-prone links

[Hila Ben Abraham]

Hi Philipp,

In the following topology a loop can be created when both A and D forward
an Interest with the same nonce to B. In this topology the Interest can be
received on two different faces.
A-->B-->C-->D
       ^             |
        -----------

Saying that, I agree that there might be cases in which processing 'looped'
Interests can be helpful. The challenge in those cases is to identify those
packets and prevent forever forwarded Interests. We started exploring
differentiating strategy transmissions fron app transmissions  as a
possible solution to the problem, but it is still work in progress. You can
find some more information in this report
<http://openscholarship.wustl.edu/cse_research/910/> (section 5.2).

Hila

On Mon, Nov 28, 2016 at 11:24 AM Gusev, Peter <peter at remap.ucla.edu> wrote:

Hi Philipp,

On related note - I used forward error correction in NDN-RTC and published
redundant data under “_parity” namespace for every video frame. This is not
related to the problem with Interests you described, but relates to lossy
links and retransmission/redundant data trade off.

Thanks,

-- 
Peter Gusev

peter at remap.ucla.edu
+1 213 5872748 <+1%20213-587-2748>
peetonn_ (skype)

Software Engineer/Programmer Analyst @ REMAP UCLA

Video streaming/ICN networks/Creative Development

On Nov 27, 2016, at 11:35 PM, Philipp Moll <philipp.moll at itec.aau.at> wrote:



Dear NDN Developers,

I’m currently thinking of methods for redundant data transmission for
real-time applications. In the case of (some) real-time applications a
retransmission of lost packets is not reasonable. Therefore I would like to
investigate redundant data transmission over multiple links. I think this
could be useful especially in wireless access networks with higher loss
rates.

My idea is, to duplicate Interests and send them out over multiple faces
(similar to Multicast). This duplication means, that the same Interest will
also arrive over multiple faces on some hosts. In order to achieve a
redundant data transmission, it is necessary that the Interest is
registered in the PIT from all in-faces.

I recognized, that the design of the Interest processing pipeline only
allows that one Interest arrives from one face. If it arrives from two or
more faces, only the first is processed, the others are classified as
looping Interests, what is disadvantageous for my intent.

I was thinking and testing a lot in order to understand this pipeline
design, but I can’t see, why Interests with the same nonce are classified
as looping if they arrive over different faces. In my opinion, a loop can
only occur if two Interests with the same nonce arrive over the same face.

This behavior also brings disadvantages in other cases. Imagine two nodes
are connected over two links, a low latency low-bandwidth link, and a high
latency high-bandwidth link. If a forwarding strategy like Multicast is
used, only the low bandwidth link would be used because the Interest is
faster at the receiver at this link. The Interest which traveled over the
high bandwidth link is classified as looping, which means that the
high-bandwidth link is not used, even if there are congestions on the
low-bandwidth link.

I would like to ask, if anyone can explain the reason for this pipeline
design or could give me advices for implementing redundant data
transmissions.

Best regards,
Philipp Moll

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