[Css-csts] RE: No MC-OCF service on AOS links?
Wolfgang.Hell at esa.int
Wolfgang.Hell at esa.int
Sun Mar 10 09:20:22 EST 2013
John,
I agree that we shall proceed as you suggest.
Best regards,
Wolfgang
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|John Pietras <john.pietras at gst.com> |
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|"Wolfgang.Hell at esa.int" <Wolfgang.Hell at esa.int> |
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|"Greenberg, Edward \(313B\)" <edward.greenberg at jpl.nasa.gov>, "Kazz, Greg J \(313B\)" <greg.j.kazz at jpl.nasa.gov>, |
|"css-csts-bounces at mailman.ccsds.org" <css-csts-bounces at mailman.ccsds.org>, "CCSDS_CSTSWG \(css-csts at mailman.ccsds.org\)" <css-csts at mailman.ccsds.org> |
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|08/03/2013 15:49 |
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|RE: [Css-csts] RE: No MC-OCF service on AOS links? |
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Wolfgang,
Greg Kazz has asked me to write a RID against the AOS SDLP specification to
request that an MC-OCF service be included. If this RID is accepted, there
will not be any need for changes to the SLE ROCF specification. So I suggest
that we not take any action on this regarding the SLE ROCF book until we see
the disposition of the RID.
Best regards,
John
-----Original Message-----
From: John Pietras
Sent: Wednesday, March 06, 2013 10:34 AM
To: 'Wolfgang.Hell at esa.int'
Cc: CCSDS_CSTSWG (css-csts at mailman.ccsds.org);
css-csts-bounces at mailman.ccsds.org; Greenberg, Edward (313B); Kazz, Greg J
(313B)
Subject: RE: [Css-csts] RE: No MC-OCF service on AOS links?
Wolfgang,
Thank you for your reply. I too favor keeping the MC option available for AOS
links, but I wanted to raise the question. I also agree that it would be nice
if the AOS SDLP book offer MC-OCF as an explicit service but that it is not
strictly necessary in order to justify the SLE ROCF delivery of those fields.
Regarding the possible need for a note - I don't have an opinion on whether
such a note is necessary, but I will point out that section 1.6.1.6 (c)
currently states the book makes use of the terms Virtual Channel or Master
Channel OCF from the AOS SDLP. That should probably be amended to delete "or
Master Channel" since MC-OCF is not to be found in the AOS SDLP book.
Best regards,
John
Ps - Martin's explanation of the undefined value for requestedGVCID makes
sense and there is no need to modify the book.
-----Original Message-----
From: Wolfgang.Hell at esa.int [mailto:Wolfgang.Hell at esa.int]
Sent: Wednesday, March 06, 2013 7:38 AM
To: John Pietras
Cc: CCSDS_CSTSWG (css-csts at mailman.ccsds.org);
css-csts-bounces at mailman.ccsds.org; Greenberg, Edward (313B); Kazz, Greg J
(313B)
Subject: Re: [Css-csts] RE: No MC-OCF service on AOS links?
John,
Your observation that ROCF permits the selection of the MC as source of the
OCFs regardless of the TFVN is correct. Given that AOS does not specify an
MC_OCF service, one could argue that ROCF should be more restrictive because
the service being 'extended' does not exist on the space link side. Looking
at the VC_OCF service specified in AOS, we see that optionally an OCF_SDU
Loss Flag may be supported which is based on checking the VC Frame Counter
being in sequence. Given that in AOS (opposite to Packet TM) there is no MC
frame counter, this mechanism for setting the OCF_SDU Loss Flag would not
work.
However, comparing the VC and MC Frame services as specified in AOS, we see
that also for the MC case a frame loss can optionally be flagged, where
however the flag is not derived from a frame counter, but rather relies on
the underlying coding sublayer flagging the loss of a frame, This mechanism
could also be used in an AOS MC_OCF service. In other words, the absence of
the MC Frame Counter is not a good reason for not having an MC_AOS service.
It is certainly correct that AOS is intended for missions with high frame
rates and that there is no need to sample the CLCW (if that is what the OCF
carries) at such high rates. On the other hand, this operational scenario
applies when the mission is in its routine phase. During LEOP the frame rate
generally is much lower and that is when COP-1 is most helpful. Missions will
not be willing to implement both AOS (for routine) and TM (for LEOP and/or
safe mode). Therefore I would favour (also for a higher degree of similarity
with TM) the addition of an MC_OCF service to AOS.
At least for now I would therefore leave ROCF as is. If deemed necessary, one
could add a note stating that for the time being an MC_OCF service over AOS
frames is not covered by a CCSDS Recommendation.
Best regards,
Wolfgang
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|John Pietras <john.pietras at gst.com>
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|"CCSDS_CSTSWG (css-csts at mailman.ccsds.org)" <css-csts at mailman.ccsds.org>
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|"Greenberg, Edward \(313B\)" <edward.greenberg at jpl.nasa.gov>, "Kazz, Greg
J \(313B\)" <greg.j.kazz at jpl.nasa.gov> |
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|05/03/2013 17:54
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|[Css-csts] RE: No MC-OCF service on AOS links?
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CSTSWG colleagues ---
I noticed yesterday that there is a disparity between the AOS and TM Space
Data Link Protocols regarding MC-OCFs – specifically, TM has an MC-OCF
service and AOS doesn’t. I asked Greg Kazz (chairman of the SLS Space Link
Protocols WG) whether this difference in behavior was intentional and if so
why, and got a response from Ed Greenberg (below).
The SLE ROCF service allows MC selection of OCFs regardless of whether the
protocol is AOS or TM.
NOTE - The Cross Support Reference Model defined separate VC-OCF and
MC-OCF services which were subsequently combined in the SLE ROCF
service, but the Reference Model didn’t exclude MC-OCFs for AOS links
either.
Is there a legitimate use case for having CLCW-bearing OCFs reporting on a TC
VC appear in every frame of a Master Channel (instead of just a single VC)?
If so, should we propose to the Space Link Protocols WG that the AOS SDLP be
changed to include an MCOCF “service” comparable to the one in the TM SDLP
stack?
If there’s not a legitimate use case, should the SLE ROCF book be modified to
restrict MC-OCF delivery to TM return links?
Best regards,
John
From: Greenberg, Edward (313B) [mailto:edward.greenberg at jpl.nasa.gov]
Sent: Monday, March 04, 2013 5:48 PM
To: Kazz, Greg J (313B); John Pietras
Subject: Re: No MC-OCF service on AOS links?
I haven't talked to Tim Ray yet about using ROCF service but I don't think
that we had envisioned MC OCF for AOS because of the nature of the channel it
was to be use on. It was for : 1)very high speed links, 2) many VCs to
service multiple independent users
3) the push was to get away from reliable frame service to reliable file
service and for high rate links COP-1 was not the best way to achieve
reliable transfer. The VC-OCF service was to support a single uplink control
channel in support of a TC uplink.
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