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<p class="MsoNormal">Dear CSTS WG (and others),<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Recently I have been involved in looking at the relationships among two of the CCSDS areas, particularly SOIS, and MOIMS, and how they use the services of the other four areas. And this work that you are doing in CSS, to develop a model
of Functional Resources, touches on these areas and also, of course, SLS and SIS. In fact, we have a side discussion starting among SOIS, SIS, and CSS to talk about the relationships among the CSS FR models, the SOIS EDS/DoT component & behavior models, and
the SIS network management models. There seem to be some areas of overlap here, and at any event we will benefit from looking at these from a global, instead of local, perspective.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">It occurs to me that this discussion about Functional Resources (FR), and which aspects and variations of space links they cover, could also benefit from stepping back to gain a broader perspective. There is always a danger in doing this
of "trying to boil the ocean", but in this case I think taking a look at this is warranted.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Here are some assertions that I would like you to consider:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<ol style="margin-top:0in" start="1" type="1">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1">CCSDS Space Data Links are made to be used in space-to-ground, ground-to-space, and space-to-space contexts.<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1">Some CCSDS space data links are designed to only operate in one of these contexts, others are intended to operate in all three.<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1">SLS has defined both fixed length SDL blocks and variable length SDL frames. This notionally includes all three operational contexts.<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1">CCSDS coding and synchronization approaches are also intended to operate in all three contexts, with similar specializations.<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1">SLS has defined both fixed and variable length coding schemes, and fixed length block and "sliced" alignment and ASM schemes, but there is not yet a complete treatment of all of these.<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1">FR, as defined in CSS CSSM, were developed in the context of ground data systems for cross support.<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1">FRs define a set of abstract data communication functions that are intended to be combined in known ways, and that may be implemented in multiple different ways and associated with
different real components.<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1">FR concepts and definitions, with little modification, could equally well be adopted in the context of space communications components, not just on the ground.<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1">EDS /DoT provides mechanisms for describing those comm components, their interfaces, and behaviors.<o:p></o:p></li></ol>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I assume that you will all agree with these assertions, and I fully expect to hear from you if you do not. Assuming that there is agreement, I propose that we ensure that the definitions that we adopt for CSS FRs cover all of these possibilities
and that we not artificially adopt limiting constraints on what these FRs are or where they may be applied. This concern about constraints is especially true for USLP, which has both fixed and variable length frame structures and is explicitly intended for
deployment in all three operational contexts.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Given this approach, and with all due respect, I suggest that you not adopt Wolfgang's stated assumption:<o:p></o:p></p>
<p style="margin-left:.5in"><span style="font-size:12.0pt">My assumption is that variable length frames will be used on the forward link only and therefore we do not need to investigate which parameters are required for the return link.</span>
<o:p></o:p></p>
<p>Using similar logic, I suggest that you also not adopt this simplifying assumption:<o:p></o:p></p>
<p style="margin-left:.5in"><span style="font-size:12.0pt">My understanding is that the FR specifications deal only with the Forward Link as emitted by an ESLT, but not with inter-spacecraft communications.<o:p></o:p></span></p>
<p>If those assumptions I stated earlier are "correct", or if we can agree on some such set of assumptions, how much work would it be to do what is suggested, and to define all of the necessary FR so that these conditions can be met? If we do this I think
that these FR concepts could see much broader use.<o:p></o:p></p>
<p>Thanks for listening.<o:p></o:p></p>
<p>Peter<o:p></o:p></p>
<p><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<div style="border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal" style="margin-left:.5in"><b><span style="font-size:12.0pt;color:black">From:
</span></b><span style="font-size:12.0pt;color:black">CSS-CSTS <css-csts-bounces@mailman.ccsds.org> on behalf of "Holger.Dreihahn@esa.int" <Holger.Dreihahn@esa.int><br>
<b>Date: </b>Wednesday, July 3, 2019 at 5:13 AM<br>
<b>To: </b>CSTS-WG <css-csts@mailman.ccsds.org><br>
<b>Subject: </b>[EXTERNAL] [Css-csts] Fw: Merging of FRs dealing with variable length frames<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:10.0pt;font-family:"Arial",sans-serif">Dear CSTS WG,</span>
<br>
<span style="font-size:10.0pt;font-family:"Arial",sans-serif">Please have a look at Wolfgang's email below. Feedback is appreciated!</span>
<br>
<br>
<span style="font-size:10.0pt;font-family:"Arial",sans-serif">Regards,</span> <br>
<span style="font-size:10.0pt;font-family:"Arial",sans-serif">Holger</span> <br>
<br>
<span style="font-size:10.0pt;font-family:"Arial",sans-serif">Holger Dreihahn<br>
European Spacecraft Operations Centre | European Space Agency | S-431<br>
+49 6151 90 2233 | </span><a href="http://www.esa.int/esoc"><span style="font-size:10.0pt;font-family:"Arial",sans-serif">http://www.esa.int/esoc</span></a>
<br>
<span style="font-size:7.5pt;font-family:"Arial",sans-serif;color:purple">----- Forwarded by Holger Dreihahn/esoc/ESA on 03/07/2019 14:09 -----</span>
<br>
<br>
<span style="font-size:7.5pt;font-family:"Arial",sans-serif;color:#5F5F5F">From: </span><span style="font-size:7.5pt;font-family:"Arial",sans-serif">"Wolfgang Hell" <wo_._he@t-online.de></span>
<br>
<span style="font-size:7.5pt;font-family:"Arial",sans-serif;color:#5F5F5F">To: </span><span style="font-size:7.5pt;font-family:"Arial",sans-serif">"Holger Dreihahn" <Holger.Dreihahn@esa.int></span>
<br>
<span style="font-size:7.5pt;font-family:"Arial",sans-serif;color:#5F5F5F">Cc: </span><span style="font-size:7.5pt;font-family:"Arial",sans-serif">"John Pietras" <john.pietras@gst.com></span>
<br>
<span style="font-size:7.5pt;font-family:"Arial",sans-serif;color:#5F5F5F">Date: </span><span style="font-size:7.5pt;font-family:"Arial",sans-serif">02/07/2019 14:49</span>
<br>
<span style="font-size:7.5pt;font-family:"Arial",sans-serif;color:#5F5F5F">Subject: </span><span style="font-size:7.5pt;font-family:"Arial",sans-serif">Merging of FRs dealing with variable length frames</span>
<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><br>
<br>
<br>
<span style="font-size:12.0pt">Hi Holger,</span> <o:p></o:p></p>
<p style="margin-left:.5in"><span style="font-size:12.0pt">can you please forward this material to the CSTS-WG? I'm copying John directly, because I suspect that he may have some more or less immediate comments while the other WG members presumably will need
more time to digest this input (as for John's input for the fixed length frames). Any early feedback WG members might have will of course be helpful.</span>
<o:p></o:p></p>
<p style="margin-left:.5in"><span style="font-size:12.0pt">My assumption is that variable length frames will be used on the forward link only and therefore we do not need to investigate which parameters are required for the return link.</span>
<o:p></o:p></p>
<p style="margin-left:.5in"><span style="font-size:12.0pt">The only Sync and Coding sublayer that may be used in combination with variable length USLP frames are CCSDS 231.0-B-3 and CCSDS 211.0-B-5, where the latter addresses the proximity link. My understanding
is that the FR specifications deal only with the Forward Link as emitted by an ESLT, but not with inter-spacecraft communications. Therefore only CCSDS 231.0-B-3 needs to be taken into account in the FR specification context. That means that the Sync and Coding
layer is the same for both USLP and TC frames and no merging of separate FR types is needed in that respect. For the sake of completeness the attached spreadsheet comparing the USLP and TC cases presents also the managed parameters of the sync and coding sublayer,
i.e., of CCSDS 231.0-B-3.If deemed useful, I can add the VOP-1 managed parameters to the next issue of the spreadsheet. Again, these parameters are common for variable length USLP and for TC frames.</span>
<o:p></o:p></p>
<p style="margin-left:.5in"><span style="font-size:12.0pt">I have applied the following color coding in the spreadsheet: Those parameters that are identical or reasonably similar so that they can be used both to monitor and, if applicable, control USLP and
TC frame handling have a green background. Those parameters that apply only to one frame type have a blue background. A red background indicates that I see a problem with merging USLP and TC or where I have a problem with the specification of the managed parameters
ar generated by the space link folks.</span> <o:p></o:p></p>
<p style="margin-left:.5in"><span style="font-size:12.0pt">As the next steps I plan to crosscheck my findings and suggestions against the material generated by John and to suggest an initial mapping of the parameters to FR types. Hopefully we can reach some
related conclusions on July 9 such that we have a reasonably stable starting point for reworking some of the FR type specifications.</span>
<o:p></o:p></p>
<p style="margin-left:.5in"><span style="font-size:12.0pt">Best regards,</span> <o:p>
</o:p></p>
<p style="margin-left:.5in"><span style="font-size:12.0pt">Wolfgang</span> <o:p></o:p></p>
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