[Nfd-dev] Help needed with debugging duplicate Nonce

[Lan Wang (lanwang)]

Junxiao,

On Jul 11, 2016, at 8:13 PM, Junxiao Shi <shijunxiao at email.arizona.edu<mailto:shijunxiao at email.arizona.edu>> wrote:

Hi Lan

When forwarder receives a Nack from face A, it records on the PIT out-record of face A that a Nack has been received, and triggers the strategy. In case Data comes from face A in the future, this Data would still be accepted.
When strategy instructs forwarder to send a Nack to face B, it removes the PIT in-record of face B. In case the PIT entry is later satisfied by Data, face B would not receive a copy of this Data.

The above highlighted part is the problem.  Since the in-record of face B is removed after sending the Nack, any Sync data packet generated by ChronoSync cannot be delivered to the neighbor on face B.  The neighbor would wait for the sync period to expire and resend the next Sync Interest to receive the data.  This is the major problem caused by the duplicate Nacks (not just pure message overhead).

To make ChronoSync work in the general case, we should design for the situation where /localhop is not used, even if there might be a workaround with /localhop.

Yes, we hope for a general solution (the forwarding plane should not generate these unnecessary Nacks).  If this is not possible, then we have to resort to a custom solution e.g. /localhop, as I said before.

Lan

Yours, Junxiao

From: Lan Wang (lanwang)<mailto:lanwang at memphis.edu>
Sent: Thursday, July 7, 2016 17:20
To: Junxiao Shi<mailto:shijunxiao at email.arizona.edu>
Cc: Ashlesh Gawande (agawande)<mailto:agawande at memphis.edu>; nfd-dev at lists.cs.ucla.edu<mailto:nfd-dev at lists.cs.ucla.edu>
Subject: Re: [Nfd-dev] Help needed with debugging duplicate Nonce

Junxiao,

I have some questions about the specifics of the example that are best clarified through the nfd call, but here are some high-order questions:

- Duplicate NACK is a problem because I think it will affect the pending interest information between the neighbors so their sync data packets won’t be able to propagate in time.  What does a node do to its PIT when it sends/receives a duplicate NACK?

- /localhop is fine for intradomain routing, because NLSR neighbors are one hop away from each other.  But we don’t have to do this if we don’t have the duplicate NACK problem in the first place.

- if we do have to use /localhop to remove the duplicate NACKs then we need to make sure that it only propagates one hop (not as implemented now).

Lan

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