[Sis-dtn] Positive reception claim vs. Negative reception claim in LTP Report Segment preparation and processing

[Keltik]

Scott Burleigh and I went through this developing CFDP/LTP three decades ago. Whilst Negative ACKs can be very efficient for bulk data in the delay/disruption environment, protocol directives such as initiation, metadata exchange, end of data, end of transaction, pause, resume etc require positive ACKs. Otherwise the state machines will never close. 

Dai

Sent from my iPhone

> On 4 Apr 2022, at 11:09, Vint Cerf via SIS-DTN <sis-dtn at mailman.ccsds.org> wrote:
> 
> 
> a system based solely on negative acks will not work.
> v
> 
> 
> On Mon, Apr 4, 2022 at 6:08 AM Felix Flentge via SIS-DTN <sis-dtn at mailman.ccsds.org> wrote:
>> Ah, yes, of course you are right. 
>> 
>> We will look into the negative ACK as part of our LTPv2 prototyping activity. 
>> 
>> Regards, 
>> Felix 
>> 
>> 
>> 
>> From:        "구철회" <chkoo at kari.re.kr> 
>> To:        <Felix.Flentge at esa.int> 
>> Cc:        "sis-dtn at mailman.ccsds.org" <sis-dtn at mailman.ccsds.org>
>> Date:        04/04/2022 11:58 
>> Subject:        RE: Re: [Sis-dtn] Positive reception claim vs. Negative reception claim in LTP Report Segment preparation and processing 
>> Sent by:        chkoo at kari.re.kr 
>> 
>> 
>> 
>> Hi Felix, 
>> 
>> I think current LTP spec quite works well with negative claim also. Consider below reception claim according to the LTP spec but negative claim. 
>> 
>> lower bound = 0 
>> upper bound = 7000 
>> negative reception claim count = 1 
>> offset = 1000 
>> length = 2000 
>> 
>> it means a receiver is requesting block of segements which starts at 1000 and length is 2000, i.e., 1000 ~ 2999, for retransmission. 
>> A sender can safely remove 2 blocks, i.e., 0 - 999 and 3000 - 7000. I think it is simpler, lower overhead and *importantly* easier to calculate (acutally no painful for localizing the target segment position). 
>> 
>> Cheol
>> --------- 원본 메일 ---------
>> 
>> 
>> 보낸사람 : <Felix.Flentge at esa.int>
>> 받는사람 : "구철회" <chkoo at kari.re.kr>
>> 참조 : "sis-dtn at mailman.ccsds.org" <sis-dtn at mailman.ccsds.org>
>> 받은날짜 : 2022-04-04 (월) 17:40:24
>> 제목 : Re: [Sis-dtn] Positive reception claim vs. Negative reception claim in LTP Report Segment preparation and processing 
>> Hi Cheol, 
>> 
>> interesting question. One thing I can think of is that the positive claims would allow you to free memory earlier while for negative claims you need to wait until the end of a session. 
>> 
>> Regards, 
>> Felix 
>> 
>> 
>> 
>> From:        "구철회 via SIS-DTN" <sis-dtn at mailman.ccsds.org> 
>> To:        "sis-dtn at mailman.ccsds.org" <sis-dtn at mailman.ccsds.org> 
>> Date:        04/04/2022 10:15 
>> Subject:        [Sis-dtn] Positive reception claim vs. Negative reception claim in LTP Report Segment preparation and processing 
>> Sent by:        "SIS-DTN" <sis-dtn-bounces at mailman.ccsds.org> 
>> 
>> 
>> Greetings,
>>  
>> This is Cheol. I am developing an LTP reference implementation. During reading the LTP specification (RFC-5326), the preparation of reception claim in Report Segment makes me confusing about why it is positive claim not negative claim for segments that were not received successfully (i.e., NAK).
>>  
>> For reference, CFDP’s NAK PDU has the negative claim structure when it is requested to report missing PDUs. Does anyone know about the background of choosing the positive claim for NAK operation in LTP?
>> I think negative claim is simpler and more efficient in terms of overhead for sender and receiver both.
>> I like to listen experts’ opinion on LTP operation and honestly hope it to be changed in newly coming LTP spec.
>>  
>> Cheol
>> 
>> 
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> 
> -- 
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