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<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;color:#1F497D">Please see my comments below.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;color:#1F497D">Best regards<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;color:#1F497D">Simon Singh<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;color:#1F497D">CCSDS SOIS Area Director<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;color:#1F497D;mso-ligatures:none">CCSDS SOIS-AP WG Chair<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;color:#1F497D;mso-ligatures:none">NASA/GSFC DTN Systems Engineer<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-family:"Calibri",sans-serif;mso-ligatures:none">From:</span></b><span style="font-family:"Calibri",sans-serif;mso-ligatures:none"> SIS-DTN <sis-dtn-bounces@mailman.ccsds.org>
<b>On Behalf Of </b>Lars Baumgaertner via SIS-DTN<br>
<b>Sent:</b> Friday, June 27, 2025 12:54 PM<br>
<b>To:</b> sis-dtn@mailman.ccsds.org<br>
<b>Subject:</b> [EXTERNAL] [BULK] [Sis-dtn] Fragmentation in BPv7 Orange Book<o:p></o:p></span></p>
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<b><span style="font-size:10.0pt;font-family:"Calibri",sans-serif;color:black;mso-ligatures:none">CAUTION:</span></b><span style="font-family:"Calibri",sans-serif;color:black;mso-ligatures:none">
</span><span style="font-size:10.0pt;font-family:"Calibri",sans-serif;color:black;mso-ligatures:none">This email originated from outside of NASA. Please take care when clicking links or opening attachments. Use the "Report Message" button to report suspicious
messages to the NASA SOC.</span><span style="font-family:"Calibri",sans-serif;color:black;mso-ligatures:none">
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<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB">While looking through the PICS tests in the latest BPv7 OB draft, I was a bit confused about the handling of fragmentation in the light of the most recent discussions.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:12.0pt;mso-ligatures:none;mso-fareast-language:EN-GB"><img width="638" height="570" style="width:6.6458in;height:5.9375in" id="Picture_x0020_1" src="cid:image001.png@01DBE76B.C802DF70"></span><span lang="EN-GB" style="font-size:12.0pt;mso-ligatures:none;mso-fareast-language:EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Fragmentation itself is OPTIONAL in #31.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">#32 is CONDITIONAL as it only makes sense if #31 is implemented.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">#34 is OPTIONAL, so BPAs can choose to do on-path ADU reassembly.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">But #33 is MANDATORY, meaning EVERY BPA must support ADU reassembly.
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">So even if we forbid fragmentation, and the feature at the source node is optional, all BPA that want to be compliant must still implement ADU reassembly logic and act upon it at the receiving end. This is quite a burden,
increases attack surface and just seems unnecessary for an optional feature and something which might be forbidden per policy in most deployments anyhow.
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-family:"Calibri",sans-serif;color:#5B9BD5">Here is my interpretation of PICS.33<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-family:"Calibri",sans-serif;color:#5B9BD5">Every implementation must support ADU
</span><span lang="EN-GB" style="color:#5B9BD5">reassembly. <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:#5B9BD5">Any node can be a destination for fragmentary bundles and the destination node of the these fragmentary (such that they have same srcID, Timestamp, Sequence Number, ADU length) is the final chance
(actually the only chance if we disregard multicasting) to recover the ADU (which the dest node must before delivering the ADU.)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:#5B9BD5">Any implementation not supporting ADU reassembly is not compliant with RFC 9171.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:#5B9BD5">“Not using fragmentation” recommendation is more like user level agreement, rather than something that is baked into the CCSDS books and we expect that to change in future.
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:#5B9BD5"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:#5B9BD5"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:#5B9BD5">wrt PICS.34<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:#5B9BD5">This actually does not make sense since the original bundle is never recovered as per RFC 9171, therefore any intermediate node that assembles ADU will not be able to forward the bundle and this
will not be compliant with RFC 9171 forwarding requirements</span><span lang="EN-GB" style="font-family:"Calibri",sans-serif;color:#5B9BD5"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Wouldn’t it make sense to make this OPTIONAL as well since consensus now seems to be not to do fragmentation at all (at least in the short to mid term)?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">One could also read the feature description as IF/WHEN doing reassembly (which itself is optional) it should then follow the rfc procedures, but then it would be CONDITIONAL, right?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Or maybe there is another way to read #33 that I missed…<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Kind regards and have a nice weekend,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Lars<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="mso-fareast-language:EN-GB">-- <o:p>
</o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="mso-fareast-language:EN-GB">Lars Baumgaertner<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="mso-fareast-language:EN-GB">Internal Research Fellow (OPS-GAE)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="mso-fareast-language:EN-GB">European Space Agency ESA/ESOC<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="mso-fareast-language:EN-GB">Robert-Bosch-Str. 5, D-64293 Darmstadt<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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