[Nfd-dev] [EXT] Trying to use NACK to trigger retransmission

[Sirapop Theeranantachai]

Just a quick update: it worked as expected!

Thank you Junxiao,
Mark

On Mon, Jul 17, 2023 at 3:34 PM Sirapop Theeranantachai <
sirapop741 at gmail.com> wrote:

> Thanks for the advice! That is a spot-on answer. I will try to use a
> helper function setexpirytimer (I wasn't aware of this) instead and will
> let you know.
>
> Mark
>
> On Mon, Jul 17, 2023, 2:50 PM Junxiao Shi <shijunxiao at arizona.edu> wrote:
>
>> Hi Sirapop
>>
>> When the incoming Nack pipeline determines that all out-records have
>> Nacked, the PIT entry is scheduled to expire "immediately".
>> Here, "immediately" means "right after the strategy has been triggered
>> for after receive Nack procedure".
>> The strategy can still access the PIT entry normally before it returns
>> from that procedure.
>>
>> If the strategy wishes to forward the Interest to an alternate path right
>> away, it should do so by invoking the send Interest action before returning
>> from the after receive Nack procedure.
>> When that happens, the PIT entry expiration is recalculated to
>> accommodate the newly created out-record, and the PIT entry would not be
>> deleted immediately.
>>
>> If the strategy wishes to hold onto the PIT entry without immediately
>> sending an outgoing Interest, it may invoke the set expiry timer helper
>> function (Strategy::setExpiryTimer).
>> This is usually used together with another timer set by the strategy
>> itself, which allows the strategy to defer the forwarding decision for a
>> short while.
>>
>> Yours, Junxiao
>>
>> On Mon, Jul 17, 2023 at 4:48 PM Sirapop Theeranantachai via Nfd-dev <
>> nfd-dev at lists.cs.ucla.edu> wrote:
>>
>>> *External Email*
>>> Hello
>>> I'm implementing a custom forwarding strategy, and would like to handle
>>> the incoming NACK to do the followings:
>>>
>>> 1) Trigger interest transmission to an eligible face
>>> 2) If no eligible face, send another NACK to incoming faces from
>>> in-records
>>> * The link type is point-to-point, so interest going back to the
>>> incoming face is not an eligible face.
>>>
>>> The problem is: forwarder.cpp will expire the PIT entry before passing
>>> to the forwarding strategy.
>>>
>>> In *NFD/daemon/fw/forwader.cpp*, line 479, under *onIncomingNack*
>>>
>>> https://github.com/named-data/NFD/blob/6bf94c02f511e3197a4e3dd77f0466d0b25d6844/daemon/fw/forwarder.cpp#L479
>>>
>>> Upon receiving nack, the forwarder.cpp will try to mark the out-record
>>> that receives the NACK. If the pit entry has no pending *out-records
>>> that are not marked*, the forwarder.cpp will set the expiry timer to be
>>> 0ms, and will be removed by the time it receives the data.
>>>
>>> One solution I tried is to reset the PIT timer, but it requires a
>>> callback to an inaccessible method *onInterestFinalize*.
>>>
>>> I discussed with Lixia and Beichuan about whether removing the PIT when
>>> all out-record receives NACK should better be handled in the forwarding
>>> strategy? I'm considerably new to the NFD code base, so please let me know
>>> if I'm wrong about this. Thank you.
>>>
>>>   // record Nack on out-record
>>>   outRecord->setIncomingNack(nack);
>>>
>>>   // set PIT expiry timer to now when all out-record receive Nack
>>>   if (!fw::hasPendingOutRecords(*pitEntry)) {
>>>     this->setExpiryTimer(pitEntry, 0_ms);
>>>   }
>>>
>>>   // trigger strategy: after receive NACK
>>>
>>> m_strategyChoice.findEffectiveStrategy(*pitEntry).afterReceiveNack(nack,
>>> ingress, pitEntry);
>>>
>>> Mark
>>>
>>>
>>> _______________________________________________
>>> Nfd-dev mailing list
>>> Nfd-dev at lists.cs.ucla.edu
>>> https://www.lists.cs.ucla.edu/mailman/listinfo/nfd-dev
>>>
>>
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