<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto">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. <div><br></div><div>Dai<br><br><div dir="ltr">Sent from my iPhone</div><div dir="ltr"><br><blockquote type="cite">On 4 Apr 2022, at 11:09, Vint Cerf via SIS-DTN <sis-dtn@mailman.ccsds.org> wrote:<br><br></blockquote></div><blockquote type="cite"><div dir="ltr"><div dir="ltr">a system based solely on negative acks will not work.<div>v</div><div><br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Mon, Apr 4, 2022 at 6:08 AM Felix Flentge via SIS-DTN <<a href="mailto:sis-dtn@mailman.ccsds.org">sis-dtn@mailman.ccsds.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><span style="font-size:10pt;font-family:sans-serif">Ah, yes, of course
you are right.</span>
<br>
<br><span style="font-size:10pt;font-family:sans-serif">We will look into
the negative ACK as part of our LTPv2 prototyping activity.</span>
<br>
<br><span style="font-size:10pt;font-family:sans-serif">Regards,</span>
<br><span style="font-size:10pt;font-family:sans-serif">Felix</span>
<br>
<br>
<br>
<br><span style="font-size:9pt;color:rgb(95,95,95);font-family:sans-serif">From:
</span><span style="font-size:9pt;font-family:sans-serif">"구철회"
<<a href="mailto:chkoo@kari.re.kr" target="_blank">chkoo@kari.re.kr</a>></span>
<br><span style="font-size:9pt;color:rgb(95,95,95);font-family:sans-serif">To:
</span><span style="font-size:9pt;font-family:sans-serif"><<a href="mailto:Felix.Flentge@esa.int" target="_blank">Felix.Flentge@esa.int</a>></span>
<br><span style="font-size:9pt;color:rgb(95,95,95);font-family:sans-serif">Cc:
</span><span style="font-size:9pt;font-family:sans-serif">"<a href="mailto:sis-dtn@mailman.ccsds.org" target="_blank">sis-dtn@mailman.ccsds.org</a>"
<<a href="mailto:sis-dtn@mailman.ccsds.org" target="_blank">sis-dtn@mailman.ccsds.org</a>></span>
<br><span style="font-size:9pt;color:rgb(95,95,95);font-family:sans-serif">Date:
</span><span style="font-size:9pt;font-family:sans-serif">04/04/2022
11:58</span>
<br><span style="font-size:9pt;color:rgb(95,95,95);font-family:sans-serif">Subject:
</span><span style="font-size:9pt;font-family:sans-serif">RE:
Re: [Sis-dtn] Positive reception claim vs. Negative reception claim in
LTP Report Segment preparation and processing</span>
<br><span style="font-size:9pt;color:rgb(95,95,95);font-family:sans-serif">Sent
by: </span><span style="font-size:9pt;font-family:sans-serif"><a href="mailto:chkoo@kari.re.kr" target="_blank">chkoo@kari.re.kr</a></span>
<br>
<hr noshade="">
<br>
<br>
<br><span style="font-size:12pt">Hi Felix,</span>
<br>
<br><span style="font-size:12pt">I think current LTP spec quite works
well with negative claim also. Consider below reception claim according
to the LTP spec but negative claim.</span>
<br>
<br><span style="font-size:12pt">lower bound = 0</span>
<br><span style="font-size:12pt">upper bound = 7000</span>
<br><span style="font-size:12pt">negative reception claim count = 1</span>
<br><span style="font-size:12pt">offset = 1000</span>
<br><span style="font-size:12pt">length = 2000</span>
<br>
<br><span style="font-size:12pt">it means a receiver is requesting block
of segements which starts at 1000 and length is 2000, i.e., 1000 ~ 2999,
for retransmission.</span>
<br><span style="font-size:12pt">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).</span>
<br>
<br><span style="font-size:12pt">Cheol</span>
<p><span style="font-size:9pt;color:rgb(0,98,225);font-family:Arial"><b>---------
원본 메일 ---------</b></span></p>
<br><span style="font-size:9pt;font-family:Arial"><b>보낸사람</b>
: <<a href="mailto:Felix.Flentge@esa.int" target="_blank">Felix.Flentge@esa.int</a>><b><br>
받는사람</b> : "구철회" <<a href="mailto:chkoo@kari.re.kr" target="_blank">chkoo@kari.re.kr</a>><b><br>
참조</b> : "<a href="mailto:sis-dtn@mailman.ccsds.org" target="_blank">sis-dtn@mailman.ccsds.org</a>" <<a href="mailto:sis-dtn@mailman.ccsds.org" target="_blank">sis-dtn@mailman.ccsds.org</a>><b><br>
받은날짜</b> : 2022-04-04 (월) 17:40:24<b><br>
제목</b> : Re: [Sis-dtn] Positive reception claim vs. Negative reception
claim in LTP Report Segment preparation and processing</span>
<br><span style="font-size:10pt;font-family:sans-serif">Hi Cheol,</span><span style="font-size:9pt;font-family:Arial">
<br>
</span><span style="font-size:10pt;font-family:sans-serif"><br>
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.</span><span style="font-size:9pt;font-family:Arial">
<br>
</span><span style="font-size:10pt;font-family:sans-serif"><br>
Regards,</span><span style="font-size:9pt;font-family:Arial"> </span><span style="font-size:10pt;font-family:sans-serif"><br>
Felix</span><span style="font-size:9pt;font-family:Arial"> <br>
<br>
<br>
</span><span style="font-size:9pt;color:rgb(95,95,95);font-family:sans-serif"><br>
From: </span><span style="font-size:9pt;font-family:sans-serif">"구철회
via SIS-DTN" <<a href="mailto:sis-dtn@mailman.ccsds.org" target="_blank">sis-dtn@mailman.ccsds.org</a>></span><span style="font-size:9pt;font-family:Arial">
</span><span style="font-size:9pt;color:rgb(95,95,95);font-family:sans-serif"><br>
To: </span><span style="font-size:9pt;font-family:sans-serif">"<a href="mailto:sis-dtn@mailman.ccsds.org" target="_blank">sis-dtn@mailman.ccsds.org</a>"
<<a href="mailto:sis-dtn@mailman.ccsds.org" target="_blank">sis-dtn@mailman.ccsds.org</a>></span><span style="font-size:9pt;font-family:Arial">
</span><span style="font-size:9pt;color:rgb(95,95,95);font-family:sans-serif"><br>
Date: </span><span style="font-size:9pt;font-family:sans-serif">04/04/2022
10:15</span><span style="font-size:9pt;font-family:Arial"> </span><span style="font-size:9pt;color:rgb(95,95,95);font-family:sans-serif"><br>
Subject: </span><span style="font-size:9pt;font-family:sans-serif">[Sis-dtn]
Positive reception claim vs. Negative reception claim in LTP Report Segment
preparation and processing</span><span style="font-size:9pt;font-family:Arial">
</span><span style="font-size:9pt;color:rgb(95,95,95);font-family:sans-serif"><br>
Sent by: </span><span style="font-size:9pt;font-family:sans-serif">"SIS-DTN"
<<a href="mailto:sis-dtn-bounces@mailman.ccsds.org" target="_blank">sis-dtn-bounces@mailman.ccsds.org</a>></span><span style="font-size:9pt;font-family:Arial">
<br>
</span>
<hr noshade=""><span style="font-size:9pt;font-family:Arial"><br>
</span>
<br><span style="font-size:10pt;font-family:sans-serif">Greetings,</span><span style="font-size:9pt;font-family:Arial">
</span>
<p style="margin-top:0px;margin-bottom:0px"><span style="font-size:10pt;font-family:sans-serif"> </span></p>
<p style="margin-top:0px;margin-bottom:0px"><span style="font-size:10pt;font-family:sans-serif">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).</span></p>
<p style="margin-top:0px;margin-bottom:0px"><span style="font-size:10pt;font-family:sans-serif"> </span></p>
<p style="margin-top:0px;margin-bottom:0px"><span style="font-size:10pt;font-family:sans-serif">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?</span></p>
<p style="margin-top:0px;margin-bottom:0px"><span style="font-size:10pt;font-family:sans-serif">I
think negative claim is simpler and more efficient in terms of overhead
for sender and receiver both.</span></p>
<p style="margin-top:0px;margin-bottom:0px"><span style="font-size:10pt;font-family:sans-serif">I
like to listen experts’ opinion on LTP operation and honestly hope it
to be changed in newly coming LTP spec.</span></p>
<p style="margin-top:0px;margin-bottom:0px"><span style="font-size:10pt;font-family:sans-serif"> </span></p>
<p style="margin-top:0px;margin-bottom:0px"><span style="font-size:10pt;font-family:sans-serif">Cheol</span></p>
<br><span style="font-size:10pt;font-family:sans-serif"><br>
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</blockquote></div><br clear="all"><div><br></div>-- <br><div dir="ltr" class="gmail_signature"><div dir="ltr"><div>Please send any postal/overnight deliveries to:</div><div>Vint Cerf</div><div>1435 Woodhurst Blvd </div><div>McLean, VA 22102</div><div>703-448-0965</div><div><br></div><div>until further notice</div><div><br></div><div><br></div><div><br></div></div></div>
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