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<p class="MsoNormal">EAWG colleagues ---<o:p></o:p></p>
<p class="MsoNormal">At today’s SAWG RASDS telecon, I took the action to upload to the SEA-SA Background Materials folder a copy of the CCSDS
<i>Standard Terminology, Conventions, and Methodology (TCM) for Defining Data Services</i> Green Book. It can be found at:<o:p></o:p></p>
<p class="MsoNormal"><a href="https://cwe.ccsds.org/sea/docs/SEA-SA/Background%20Materials/CCSDS-TCM_GreenBook.zip">https://cwe.ccsds.org/sea/docs/SEA-SA/Background%20Materials/CCSDS-TCM_GreenBook.zip</a><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Because the book is now 16 years old, I included a READ-ME that briefly explains the background, subsequent use, and current applicability of the book, which is as follows:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-left:.5in">At the inception of the Space Link Extension (SLE) transfer services in the early 1990s, there was wide confusion about the nature of the “cross support” services, when the most-publicized model for communication
services was the ISO Open System Interconnection (OSI) 7-layer model, which addresses “service” as the thing that one layer of a communication protocol stack provides to the layer above it. What was needed for SLE was a “service language” that addressed the
peer-to-peer relationship that exists in cross support situations among space Agencies.
<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-left:.5in">At the time, the best such model was the Abstract Service Definition Conventions (ASDC), an ISO standard (at the time) that was an abstraction and generalization of the ISO Remote Operations standards.
<i>The Standard Terminology, Conventions, and Methodology (TCM) for Defining Data Services</i> Green Book (CCSDS 910.2-G-1, November 1994) was written explain the difference between the two approaches and show how they related to each other. The Cross Support
Services Area adopted ASDC as the conceptual basis for SLE services (and, subsequently, for Cross Support Transfer Services), although the approach is generally applicable to cross support services in general. The CCSDS
<i>Cross Support Reference Model, Part 1 – Space Link Extension Services</i> Blue Book (CCSDS 910.4) – the basic architecture and set of requirements for all SLE services - adopted the applicable concepts and terminology from ASDC.<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-left:.5in">Subsequently ISO deprecated ASDC as an international standard. Because the terminology and approach were so ingrained in SLE services, subsequent versions of CCSDS 910.4 became the normative home of those terms
and concepts.<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-left:.5in">Newer sets of terminology for describing peer-to-peer service relationships have evolved in the intervening years. Nevertheless, the fundamental contrasts and comparisons between the ISO/OSI model and ASDC are still
applicable to an understanding of why the ISO/OSI model is not appropriate for framing cross support services.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Best regards,<o:p></o:p></p>
<p class="MsoNormal">John<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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