<span style=" font-size:10pt;font-family:sans-serif">Hi Carlo,</span>
<br>
<br><span style=" font-size:10pt;font-family:sans-serif">I assume there
could be advantages of intermediate checkpoints in cases where the duration
of the session >> RTT (could reduce overall latency, on-board memory
could be freed).</span>
<br>
<br><span style=" font-size:10pt;font-family:sans-serif">I certainly like
the idea of a blocklifetime. It could maybe even be an optional parameter
of the Transmission.request (which might need some changes anyway because
of the removal of mixed sessions).</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:#5f5f5f;font-family:sans-serif">From:
</span><span style=" font-size:9pt;font-family:sans-serif">"Carlo
Caini" <carlo.caini@unibo.it></span>
<br><span style=" font-size:9pt;color:#5f5f5f;font-family:sans-serif">To:
</span><span style=" font-size:9pt;font-family:sans-serif">"Felix.Flentge@esa.int"
<Felix.Flentge@esa.int>, "Tomaso.deCola@dlr.de" <Tomaso.deCola@dlr.de></span>
<br><span style=" font-size:9pt;color:#5f5f5f;font-family:sans-serif">Cc:
</span><span style=" font-size:9pt;font-family:sans-serif">"sis-dtn@mailman.ccsds.org"
<sis-dtn@mailman.ccsds.org></span>
<br><span style=" font-size:9pt;color:#5f5f5f;font-family:sans-serif">Date:
</span><span style=" font-size:9pt;font-family:sans-serif">26/02/2021
09:01</span>
<br><span style=" font-size:9pt;color:#5f5f5f;font-family:sans-serif">Subject:
</span><span style=" font-size:9pt;font-family:sans-serif">RE:
[Sis-dtn] Telecon Notes 20210224</span>
<br>
<hr noshade>
<br>
<br>
<br><tt><span style=" font-size:10pt">Dear Felix,<br>
I agree with you that the text is difficult to understand,
but I would ascribe the problem to the protocol, which is maybe too complex.
In particular, 1) the possibility of inserting CP before of the final segment
of a block and 2) the possibility of sending multiple RS in response to
the same CP, make the the protocol most likely more complex than necessary,
and in turn, also difficult to describe.<br>
My interpretation of the text (I am not sue too) is that at the first Tx
attempt, the oustanding CPs are 1) the compulsory CP that flags the latest
segment; 2) any other gratuitous CP that may be inserted before the latest
segment. Each of these CP triggers one or more RS, depending on the number
of claims; these RSs, one recived, trigger data ReTx and new CPs, belonging
to the first Re-Tx cycle and so on. It is diffiucult to explain and to
implement.<br>
Now, if you remove the possibility of inserting intermediate CPs (actually,
they are never inserted by ION), things start to improve. By the way, with
a propagation delay that is dominant on the "radiation time",
in my opinion there is not any advantage in using intermediate CPs. Let
us assume that the RTT is 6 minutes and that the radiationtime is 1s. What
is the advantage of receiving an intermediate CP at, say 500ms before the
last segment flagged as CP? It would just generate an RS 500ms before the
last, thus reTx could start 500ms before, which seems of little help, considering
the 3600 s RTT.<br>
The possibility of spreading claims on multiple RS is manageable (ION does),
but it makes once again maybe more complex than necesary the algorithm,
as multiple RSs means multiple CPs (the "oustanding ones" in
my interpretation) for each Re-Tx cycle.<br>
Last comment, I agree once again with you that many conditions could suggest
the closing of an ongoing sessions. To those you mentioned I would add
the duration of a session. I mean that in my opinion a session should have
a time limit. Suppose that an RS is followed by an RAS (RS ACK), but not
by any retranmissions for whatever reason (the Tx is lazy or worse...).
On the Rx side a buffer plenty of data would be kept forever as the RS
was confirmed by the RAS...<br>
A second reson for a time limit, is that a block should have a lifetime,
as bundles. Otherwise is pefectly possible, in the presence of a scheduled
intermittent link, that a session stay frozen for hours and that during
this time the content of the block, i.e. a bundle, expires. Is a non-sense
that, at the next, contact LTP carry on a session whose content is to be
discarded as soon as passed to BP. This could be easily avoided by associating
a blocklifetime (<=bundle_lifetime) to every session.<br>
Yours,<br>
carlo <br>
<br>
<br>
<br>
________________________________________<br>
Da: SIS-DTN [sis-dtn-bounces@mailman.ccsds.org] per conto di Felix.Flentge@esa.int
[Felix.Flentge@esa.int]<br>
Inviato: venerd́ 26 febbraio 2021 08:08<br>
A: Tomaso.deCola@dlr.de<br>
Cc: sis-dtn@mailman.ccsds.org<br>
Oggetto: Re: [Sis-dtn] Telecon Notes 20210224<br>
<br>
Hi Tomaso,<br>
<br>
maybe I am just confused but I have some difficulties to understand what
this text actually means (in particular, what is meant by all outstanding
CP segments?). It also seems dependent on the sender's strategy when to
send CPs.<br>
<br>
Actually, looking at 6.13 I am wondering whether we need this at all. 6.13
allows to cancel a session with RLEXC if the number of transmission problems
exceeds an established limit. Maybe this could also cover re-transmission
cycle limits?<br>
<br>
Thinking about this, I believe we need to leave some room for implementation-specific
limits which could come in a lot of different flavours (absolute re-transmitted
amount of data, relative re-transmitted amount of data, number of queued
segments for re-transmission, ....). It just seems strange that for one
of these 'implementation-specific' limits we have a specific error code
(RXMTCYCEXC).<br>
<br>
Regards,<br>
Felix<br>
<br>
<br>
<br>
From: <Tomaso.deCola@dlr.de><br>
To: <kscott@mitre.org>, <sis-dtn@mailman.ccsds.org>,
<Felix.Flentge@esa.int><br>
Date: 25/02/2021 14:17<br>
Subject: RE: Telecon Notes 20210224<br>
________________________________<br>
<br>
<br>
<br>
Hi All,<br>
<br>
<br>
<br>
Concerning the point on the retransmission cycle limit, this is first appearing
on RFC 5326 at the end of section 6.2.2 (beginning of page 34) and copied
here below for your convenience:<br>
<br>
<br>
<br>
There may be other implementation-specific limits that may cause an<br>
<br>
LTP implementation to initiate session-cancellation procedures.
One<br>
<br>
such limit is the maximum number of retransmission-cycles seen.
A<br>
<br>
retransmission cycle at the LTP Sender comprises the two related<br>
<br>
events: the transmission of all outstanding CP segments from the<br>
<br>
sender, and the reception of all RS segments issued from the receiver<br>
<br>
in response to those CP segments. A similar definition would
apply<br>
<br>
at the LTP Receiver but relate to the reception of the CP segments<br>
<br>
and transmission of all RS segments in response. Note that
the<br>
<br>
retransmitted CP and RS segments remain part of their original<br>
<br>
retransmission-cycle. Also, a single CP segment may cause
multiple<br>
<br>
RS segments to be generated if a reception report would not fit
in a<br>
<br>
single data link-MTU-sized RS segment; all RS segments that are
part<br>
<br>
of a reception report belong to the same retransmission cycle to<br>
<br>
which the CP segment belongs. In the presence of severe channel<br>
<br>
error conditions, many retransmission cycles may elapse before
red-<br>
<br>
part transmission is deemed successful; an implementation may<br>
<br>
therefore impose a retransmission-cycle limit to shield itself
from a<br>
<br>
resource-crunch situation. If an LTP sender notices the<br>
<br>
retransmission-cycle limit being exceeded, it SHOULD initiate the<br>
<br>
Cancel Session procedure (Section 6.19<</span></tt><a href="https://tools.ietf.org/html/rfc5326#section-6.19"><tt><span style=" font-size:10pt">https://tools.ietf.org/html/rfc5326#section-6.19</span></tt></a><tt><span style=" font-size:10pt">>),
queuing a CS segment with<br>
<br>
reason-code RXMTCYCEXC and sending a transmission-session<br>
<br>
cancellation notice (Section 7.5<</span></tt><a href="https://tools.ietf.org/html/rfc5326#section-7.5"><tt><span style=" font-size:10pt">https://tools.ietf.org/html/rfc5326#section-7.5</span></tt></a><tt><span style=" font-size:10pt">>)
to the client service.<br>
<br>
<br>
<br>
@Felix.Flentge@esa.int<</span></tt><a href=mailto:Felix.Flentge@esa.int><tt><span style=" font-size:10pt">mailto:Felix.Flentge@esa.int</span></tt></a><tt><span style=" font-size:10pt">>:
which aspects did you want to make normative?<br>
Best Regards,<br>
<br>
Tomaso<br>
<br>
<br>
<br>
<br>
<br>
From: SIS-DTN <sis-dtn-bounces@mailman.ccsds.org> On Behalf Of Dr.
Keith L Scott<br>
Sent: Mittwoch, 24. Februar 2021 17:52<br>
To: sis-dtn@mailman.ccsds.org<br>
Subject: [Sis-dtn] Telecon Notes 20210224<br>
<br>
<br>
<br>
SIS-DTN Telecon<br>
<br>
<br>
<br>
LTP<br>
<br>
Took some notes in the SharePoint List here:<br>
<br>
</span></tt><a href=https://cwe.ccsds.org/fm/wiki/Lists/SISDTN%20LTP%20Update%202021/AllItems.aspx><tt><span style=" font-size:10pt">https://cwe.ccsds.org/fm/wiki/Lists/SISDTN%20LTP%20Update%202021/AllItems.aspx</span></tt></a><tt><span style=" font-size:10pt"><br>
<br>
What testing / experimentation to drive out issues?<br>
<br>
• LTP Extension Header vs. small Green Blocks to signal adaptive coding
and modulation.<br>
<br>
• ESA looking to use LTP for optical; no experimentation expected for
8-12 months<br>
<br>
ReTx cycle limit & Discretionary Checkpoints<br>
<br>
People to come up with draft clarifying language and we’ll review. Consult
the RFC5326 text to see if we want to ‘normativeize’ it. Keith
to collect text from RFC5326 to provide context.<br>
<br>
BPv7<br>
<br>
Keith to build a list of items like the LTP list for discussion at next
meeting.<br>
<br>
BPSec<br>
<br>
In Security WG processing; we need to notify them of status of BPSec doc
in IETF.<br>
<br>
<br>
<br>
People need to review current draft and we’ll work any proposed changes
to the SEA-SEC WG ASAP:<br>
<br>
</span></tt><a href="https://tools.ietf.org/html/draft-ietf-dtn-bpsec-27"><tt><span style=" font-size:10pt">https://tools.ietf.org/html/draft-ietf-dtn-bpsec-27</span></tt></a><tt><span style=" font-size:10pt"><br>
<br>
<br>
<br>
Default security context from IETF is probably not what we want in CCSDS;
we might need to define our own set.<br>
<br>
<br>
<br>
ESA to start an activity on security.<br>
<br>
NM Books<br>
<br>
Links to I-Ds<br>
<br>
NM books going through IETF, about to become WG documents, changes as a
result of reviews may be coming over the next 8-12 months.<br>
<br>
<br>
<br>
ICPA Need Dates for NM updated to 2028, we can prioritize the other
efforts above these.<br>
<br>
<br>
<br>
</span></tt>
<br>
<br>