[Sls-slp] Adding provision in AOS SDLP for extending the Version 2 SCID

[Kazz, Greg (US 312B)]

Dear SLP WG,

CCSDS has been informed that missions are requesting additional Version 2 (AOS) SCIDs. However, there are no more available.
Therefore, the Spacecraft Engineering Area Director, Peter Shames has approached me with the request to extend the AOS SCID. This solution has the support of the CESG chair and several others in the CCSDS management chain.

Attached is the current version of all the changes the SLP WG has accumulated associated with the AOS SDLP including the extension of the First Header Pointer (FHP) and the update to the FHEC field. We were holding these changes in order to issue them all in the 5-year review coming up in January 2025. However, due to the urgency of providing additional Version 2 SCIDs, it seems very prudent to move forward with these changes and come to consensus on this latest update i.e., extending the current 8-bit SCID to a 10-bit SCID. We can achieve this by using the 2-bits of spare in the Signaling Field of the AOS Primary Transfer Frame Header defined in Section 4.1.2.5.4. These spares would then become the “SCID Extension” field, which would be pre-pended to the existing 8-bit SCID to create a 10-bit SCID, if needed by a given mission. If not needed, the value would remain ‘00’. Ergo, we remain backward compatible with existing implementations.

Please review the changes in the attachment I have made in the SCID field (Section 4.1.2.2.3), and also the Figure 4-2, 4.1.2.5.1.3, and 4.1.2.5.4, the new SCID Extension field and come prepared to let us know if I missed anything. I will place this draft into the CWE as well today.

On the other hand, if you have strong reservations as to why these changes should NOT be made, please let us know as well.

Best regards,
Greg Kazz
Chair SLP WG

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