[Sls-slp] Results of Discussion with Takahiro Yamada on Revising SPP Blue Book

[John Pietras]

All,

In an earlier email in this thread, Greg commented that he understood that many missions multiplex different "packet channels" into the same VC, but that he did not see this happening in an interoperable way. I think that Greg has hit on the important factor here - what is exposed in an interoperable, cross-supported way?



Back when we wrote the original AOS book, we had the notion that "cross support" users would be able to access individual packet channels via standard intefaces. This notion was formalized in the Cross Support Reference Model, Part 1 - Space Link Extension Services Blue Book (colloquially known as the "SLE Ref Model"), which envisioned two "flavors" of Forward Space Packet (TC and AOS) and one Return Space Packet service. Those services would have allowed multiple FSP instances to carry packete channels all destined for the same VC.



As it turned out, only the TC flavor of the Forward Space Packet service was ever realized.  Different instances of the (TC) FSP service are indeed capable of carrying different packet channels destined for the same VC. The FSP service uses MAP, so the necessary packet channel multiplexing into VCs is accomplished (indirectly) through MAP Multiplexing.



But had the AOS FSP been realized, it *would* have required the packet channel muxing that currently resides in the SPP. But since it wasn't realized, the main use case (that I know of) disappears, and perhaps packet channel multiplexing is indeed no longer needed at a cross-support interoperability level, which I agree with Greg is the important factor in considering whether to retain the specification in the SPP (or migrate it back into one or more of the SDLP books).



Best regards,

John





From: Gian.Paolo.Calzolari at esa.int [mailto:Gian.Paolo.Calzolari at esa.int]
Sent: Tuesday, January 30, 2018 8:55 AM
To: Kazz, Greg J (312B)
Cc: John Pietras; sls-slp at mailman.ccsds.org; SLS-SLP
Subject: Re: [Sls-slp] Results of Discussion with Takahiro Yamada on Revising SPP Blue Book



Greg,
        what we have to be sure it captured in our CCSDS  books is the following situation (e.g. for a TM/AOS link)

  *   There multiple sources generating packet contents and asking creation of packets
  *   Those packets are created with different APIDs depending on the source
  *   Those different APIDs shall be multiplexed to produce a single packet stream:
  *   This single packet stream is then injected in in a VC
  *

It is then correct that "The current AOS SDLP version i.e., CCSDS 732.0-B-3 Sept 2015 is agnostic about "packet channels"  and "Individual CCSDS packets from multiple sources" (implying multiple APIDs). It is really only concerned about multiplexing of packets with different PVNs onto VCs." In fact AOS would only see that single stream.

All the rest shall be done above the SDLP.

We shall check also what we lost with respect to CCSDS 103.0-B-2 (now silver) where there was a nice picture for which I attach a detail.
Another document to be checked for losses is CCSDS 203.0-B-2 and even FSP that mention APID multiplexing if I remember well.

Finally we shall verify all fits within the encapsulation service.

Ciao

Gian Paolo
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