<font size=2 face="sans-serif">Dear Peter,</font>
<br><font size=2 face="sans-serif">When I talk about CFDP below, I mean
CFDP class 2. DTN would of course be the technically sound solution to
a lot of problems and we would not need to invent new services. However,
in practice the adoption of CFDP class two was apparently what was possible
for the next generation of satellites. On top of that, flight control teams
often insist on being in control of everything going up to the spacecraft,
so we invented the CSTS Return CFDP PDU service to relay CFDP PDUs (NAK
etc.) from the ESLT to the EUN, where the CFDP PDUs are merged into the
CLTUs anyway sent from the EUN to the ESLT and finally the spacecraft.
At that point SLE CLTU does the job, although it's clear that CSTS Forward
Frame is needed for high rate uplinks, or would allow closure of the CFDP
class 2 protocol loop in the ESLT.</font>
<br>
<br><font size=2 face="sans-serif">The feature of the reduced CFDP PDUs
we envisage for a more complicated scenario: Here CFDP class 2 shall be
used to transfer files from the spacecraft over several ESLTs to a central
location on ground (payload processing). No BP involved unfortunately.</font>
<br>
<br><font size=2 face="sans-serif">I hope that clarifies some aspects.</font>
<br>
<br><font size=2 face="sans-serif">Best regards,</font>
<br><font size=2 face="sans-serif">Holger</font>
<br>
<br><font size=2 face="sans-serif">Holger Dreihahn<br>
European Spacecraft Operations Centre | European Space Agency | H-293<br>
+49 6151 90 2233 | </font><a href=http://www.esa.int/esoc><font size=2 face="sans-serif">http://www.esa.int/esoc</font></a>
<br>
<br>
<br>
<br><font size=1 color=#5f5f5f face="sans-serif">From:
</font><font size=1 face="sans-serif">"Shames, Peter
M (US 312B)" <peter.m.shames@jpl.nasa.gov></font>
<br><font size=1 color=#5f5f5f face="sans-serif">To:
</font><font size=1 face="sans-serif">"Holger.Dreihahn@esa.int"
<Holger.Dreihahn@esa.int></font>
<br><font size=1 color=#5f5f5f face="sans-serif">Cc:
</font><font size=1 face="sans-serif">"Barkley, Erik
J (US 3970)" <erik.j.barkley@jpl.nasa.gov>, "Gian Paolo
Calzolari" <Gian.Paolo.Calzolari@esa.int>, "Gilles Moury"
<Gilles.Moury@cnes.fr>, "Kazz, Greg J (US 312B)" <greg.j.kazz@jpl.nasa.gov>,
"Wilmot, Jonathan J. (GSFC-5820)" <jonathan.j.wilmot@nasa.gov>,
"Klaus-Juergen Schulz" <Klaus-Juergen.Schulz@esa.int>,
"Keith Scott" <kscott@mitre.org>, "Sanchez Net, Marc
(US 332H)" <marc.sanchez.net@jpl.nasa.gov>, "Margherita.di.Giulio@esa.int"
<Margherita.di.Giulio@esa.int>, "Burleigh, Scott C (US 312B)"
<scott.c.burleigh@jpl.nasa.gov>, "SEA-SA" <sea-sa@mailman.ccsds.org></font>
<br><font size=1 color=#5f5f5f face="sans-serif">Date:
</font><font size=1 face="sans-serif">11/01/2021 23:51</font>
<br><font size=1 color=#5f5f5f face="sans-serif">Subject:
</font><font size=1 face="sans-serif">Re: [EXTERNAL]
Re: Request for a special working meeting on some key Cross Support architecture
document issues</font>
<br>
<hr noshade>
<br>
<br>
<br><font size=3 face="sans-serif">Dear Holger,</font>
<br><font size=3 face="sans-serif"> </font>
<br><font size=3 face="sans-serif">Thanks for the reply re what you are
contemplating. It helps to offer an understanding of what you have
been thinking about.</font>
<br><font size=3 face="sans-serif"> </font>
<br><font size=3 face="sans-serif">If I read this correctly we will still
need to deploy the FF-CSTS in the ESLT and to provide the necessary CFDP
agent software and associated “plumbing” to accommodate this insertion
of functionality. And then we will also need, on top of that, to
define this new “</font><font size=3 face="Arial">CSTS Return CFDP PDU
Service</font><font size=3 face="sans-serif">”, to splice this “</font><font size=3 face="Arial">reduced
CFDP File Data PDU delivery function” into the CFDP agent, and also define
how these new, specialized, “monitor” and “control” interfaces are
to work.</font>
<br><font size=3 face="Arial"> </font>
<br><font size=3 face="Arial">This still looks like several (at least three)
new protocols or adaptations of services to accomplish something that “ought
to be” simple. But then, things are seldom as simple as we would
like them to be.</font>
<br><font size=3 face="Arial"> </font>
<br><font size=3 face="Arial">As a side question, was any sort of trade
study done to evaluate the use of DTN to accomplish this instead? That
has the advantage, at least from my point of view, of being an approach
that moves us into a space internetworking future, even as it brings its
own complexities. Was this even considered?</font>
<br><font size=3 face="Arial"> </font>
<br><font size=3 face="Arial">Thanks, Peter</font>
<br><font size=3 face="sans-serif"> </font>
<br><font size=3 face="sans-serif"> </font>
<br><font size=3 face="sans-serif"><b>From: </b>"Holger.Dreihahn@esa.int"
<Holger.Dreihahn@esa.int><b><br>
Date: </b>Monday, January 11, 2021 at 1:21 AM<b><br>
To: </b>Peter Shames <peter.m.shames@jpl.nasa.gov><b><br>
Cc: </b>Erik Barkley <erik.j.barkley@jpl.nasa.gov>, Gian Paolo Calzolari
<Gian.Paolo.Calzolari@esa.int>, Gilles Moury <Gilles.Moury@cnes.fr>,
Greg Kazz <greg.j.kazz@jpl.nasa.gov>, "Wilmot, Jonathan J. (GSFC-5820)"
<jonathan.j.wilmot@nasa.gov>, Klaus-Juergen Schulz <Klaus-Juergen.Schulz@esa.int>,
Keith Scott <kscott@mitre.org>, Marc Sanchez Net <marc.sanchez.net@jpl.nasa.gov>,
"Margherita.di.Giulio@esa.int" <Margherita.di.Giulio@esa.int>,
Scott Burleigh <scott.c.burleigh@jpl.nasa.gov>, SEA-SA <sea-sa@mailman.ccsds.org><b><br>
Subject: </b>[EXTERNAL] Re: Request for a special working meeting on some
key Cross Support architecture document issues</font>
<br><font size=3 face="sans-serif"> </font>
<br><font size=3 face="Arial">Dear Peter,</font><font size=3 face="sans-serif">
</font><font size=3 face="Arial"><br>
At ESA we have looked at similar problems for a CFDP entity running in
a ground station (ESLT) and a MOC (EUN) being 'in control' of SC and potentially
some items (CFDP) in the ESLT. We have come up with some internal conclusions
and suggestions, we would be more than happy to discuss them with you:</font><font size=3 face="sans-serif">
<br>
</font><font size=3 face="Arial"><br>
- We propose a new CSTS Return CFDP PDU Service. This is currently an ESA
draft of a CSTS Services returning CFDP PDUs from an ESLT to the EUN in
a standardized way. It also offers a reduced CFDP File Data PDU delivery,
which is required to analyze the CFDP protocol in realt time at the EUN
for some reason, but the bandwidth on the spacelink is (much) higher than
from the ESLT to the EUN. In the context below it may or may not be required,</font><font size=3 face="sans-serif">
</font><font size=3 face="Arial"><br>
- to Monitor the CFDP entity in an ESLT, we foresee the CSTS Monitored
Data Service with the Functional Resource Model providing a CFDP entity
Functional resource, a CFDP entity has been part of the Functional Resource
Model review (Tier 1). That monitoring can of course be extended to what
is required in terms of 'out of band report'</font><font size=3 face="sans-serif">
</font><font size=3 face="Arial"><br>
- To control the CFDP entity in an ESLT, we envisage a CSTS Service Control,
being able to send control directives from e.g.an EUN to an ESLT. The available
control directives are again provided by the Functional Resource Model</font><font size=3 face="sans-serif">
<br>
</font><font size=3 face="Arial"><br>
Best regards,</font><font size=3 face="sans-serif"> </font><font size=3 face="Arial"><br>
Holger </font><font size=3 face="sans-serif"><br>
</font><font size=3 face="Arial"><br>
Holger Dreihahn<br>
European Spacecraft Operations Centre | European Space Agency | H-293<br>
+49 6151 90 2233 | </font><a href="https://urldefense.us/v3/__http:/www.esa.int/esoc__;!!PvBDto6Hs4WbVuu7!cJsRPsli-tBkSSqasuAM5DVQCgkvU90ZKmySQ2ydkhPH3PQLZzMEN7DE5pUhhsIb-p34mzZV$"><font size=3 color=blue face="Arial"><u>http://www.esa.int/esoc</u></font></a><font size=3 face="sans-serif">
<br>
<br>
<br>
</font><font size=3 color=#5f5f5f face="Arial"><br>
From: </font><font size=3 face="Arial">"Shames,
Peter M (US 312B)" <peter.m.shames@jpl.nasa.gov></font><font size=3 face="sans-serif">
</font><font size=3 color=#5f5f5f face="Arial"><br>
To: </font><font size=3 face="Arial">"Barkley,
Erik J (US 3970)" <erik.j.barkley@jpl.nasa.gov>, "Holger
Dreihahn/esoc/ESA" <Holger.Dreihahn@esa.int>, "Burleigh,
Scott C (US 312B)" <scott.c.burleigh@jpl.nasa.gov>, "Keith
Scott" <kscott@mitre.org>, "Sanchez Net, Marc (US 332H)"
<marc.sanchez.net@jpl.nasa.gov>, "Gian Paolo Calzolari"
<Gian.Paolo.Calzolari@esa.int>, "Gilles Moury" <Gilles.Moury@cnes.fr>,
"Kazz, Greg J (US 312B)" <greg.j.kazz@jpl.nasa.gov>, "Wilmot,
Jonathan J. (GSFC-5820)" <jonathan.j.wilmot@nasa.gov></font><font size=3 face="sans-serif">
</font><font size=3 color=#5f5f5f face="Arial"><br>
Cc: </font><font size=3 face="Arial">"SEA-SA"
<sea-sa@mailman.ccsds.org>, "Klaus-Juergen Schulz" <Klaus-Juergen.Schulz@esa.int>,
"Margherita.di.Giulio@esa.int" <Margherita.di.Giulio@esa.int></font><font size=3 face="sans-serif">
</font><font size=3 color=#5f5f5f face="Arial"><br>
Date: </font><font size=3 face="Arial">07/01/2021
20:00</font><font size=3 face="sans-serif"> </font><font size=3 color=#5f5f5f face="Arial"><br>
Subject: </font><font size=3 face="Arial">Request
for a special working meeting on some key Cross Support architecture document
issues</font><font size=3 face="sans-serif"> </font>
<div align=center>
<hr noshade></div>
<br><font size=3 face="sans-serif"><br>
<br>
<br>
Dear CCSDS colleagues, <br>
<br>
I want to start by wishing you all a very happy and prosperous New Year.
I do this in spite of the recent horrifying news that a mob of hooligans,
domestic terrorists, attacked the US Capitol yesterday. Optimist
that I am, I am sure we will put this behind us. I hope I am not
wrong in this. <br>
<br>
That diversion aside, I wish to enlist all of you in looking at a set of
issues that have just some up in the process of tackling the updates to
the Space Communication Cross Support (SCCS) Architecture documents (ARD
/ ADD), the SCCS-ARD, CCSDS 901.1-M-1. You all know that as part
of the updates to this document we have been asking for feedback on recently
published standards (since 2015) and on new standards that are in work
now and that are expected to be published in the next 3-5 years. If
you have not yet provided your inputs please do so as soon as you can.
<br>
<br>
The following is a rather long description of what has turned out to be
a somewhat complicated set of issues. This email is an attempt to
lay out the issues so that you can consider them ahead of time, but we
are aware that an actual face-to-face (virtual) discussion, and likely
some work in one or more WGs, will be called for to reach a useful conclusion.
<br>
<br>
What I wish to focus on in this discussion is a set of issues specifically
related to the following topics: </font>
<ol>
<li value=1><font size=3 face="sans-serif">A key assumption that has been
made, based on the SISG Study from 2009, and reflected in the SCCS-ADD/ARD,
is that any Earth User Node (EUN, nominally the MOC) that controls and
operates a Space User Node (SUN, colloquially known a spacecraft) or a
Space Relay Node (SRN) that offers DTN or other relay services, will want
to be able to directly command that spacecraft and get at least engineering
telemetry from that spacecraft. This EUN is said to “own” the spacelink
and have control over it. And the act of planning, scheduling, and
configuring that space link is what allows all other traffic to then flow
using the link. </font>
<li value=2><font size=3 face="sans-serif">A further key assumption is
that for any of the EUNs that operate a spacecraft that offers such relay
or network services, or that use the forward and return file service, is
that the Earth Space Link Terminal (ESLT, nominally a ground station and
associated processing equipment including SM, SLE, and CSTS) will implement
the Forward Frame CSTS (FF-CSTS) which is designed to integrate data flows
from multiple Earth User Nodes and to interface to CFDP, DTN, frame merging,
and frame creating production functions within the ESLT. This is
the fundamental architectural “production plumbing” that allows all of
this stuff to work together. There are a couple of slides from the
SCCS ARD that illustrate this plumbing, as defined. </font>
<li value=3><font size=3 face="sans-serif">Missions may use (and ESLTs
may implement) a forward and return “file service”, that uses TGFT to
transfer files from the EUN to the ESLT, along with a CFDP “agent” in
the ESLT that does the actual file delivery transfer, using CFDP, over
the space link to the Space User Node (SUN, otherwise known as the spacecraft).
</font>
<li value=4><font size=3 face="sans-serif">One of the recently recognized
considerations that this particular deployment architecture creates a need
for some sort of special, out of band, signaling of missing data reports
on the return link to the EUN from the CFDP agent in the ESLT. This
is a sort of “control report” that the EUN can deal with to control re-transmission,
which may include sending retransmission requests back to the CFDP agent
in the ESLT or requests to abandon the session and accept a partial file.
</font>
<li value=5><font size=3 face="sans-serif">This also requires some as yet
unrecognized protocol that will allow the CFDP agent in the ESLT to send
these “control reports”. </font>
<li value=6><font size=3 face="sans-serif">This scenario also requires
some as yet unrecognized control protocol, which is needed for the EUN
to somehow signal the ESLT just how it wants that file to be broken into
PDUs in the first place, and how those PDUs are to be framed into some
virtual channel and merged into the master frame stream within the ESLT.
As yet there is no protocol defined to do this. </font>
<li value=7><font size=3 face="sans-serif">There must be some clear definition
of how all of the features of this “File delivery protocol” are to be
defined so that it can use the features of the TGFT, which is just a file
transfer mechanism with none of this sort of control framework nor back
and forth signaling.</font></ol><font size=3 face="sans-serif"> <br>
This is some sort of “cross support protocol” that belongs in the CSS
Area, whether it is in the CSTS WG or the SM WG. That said, it may
also require some sort of “control report” interface to be spliced into
the CFDP protocol agent to allow the EUN to be signaled about intermediate
CFDP protocol status, along with some sort of “control interface” that
will allow the CFDP agent, in the ESLT, to be controlled from the EUN.
And there also must be some means for the EUN to tell the CFDP agent
in the ESLT just how to turn that file into CFDP PDUs, link layer PDUs,
encapsulate them, and how to merge them into the uplink traffic flow. <br>
<br>
In discussing this we also delved into how best to represent the needed
“production plumbing” in the ESLT. The nominal CFDP deployment
from the outset was understood to be an application layer CFDP Agent in
the EUN and another peer application layer CFDP agent in the SUN. This
new service breaks that paradigm and adds what is starting to look like
a significant bit of new CCSDS protocol plumbing in order to make it all
work right with this asymmetrical protocol arrangement. Of course,
we could just throw up our hands and say “do it by management”, but that
is not an interoperable approach by any normal meaning of the term. <br>
<br>
To be frank, realizing that we will now need to create this brand new set
of specialized control and signaling protocols, for this one special case,
probably ought to cause us to question whether it makes sense to define
this new service at all, as opposed to just deploying the CFDP agent in
the end nodes of the space link, as it was defined. We will not address
it further here, but it appears to be an option that must be considered
as well. <br>
<br>
In talking about this in the SAWG meeting on 6 Jan 21 the following questions
and observations came up. <br>
</font>
<ol>
<li value=1><font size=3 face="sans-serif">The returned “control report”
from the CFDP agent in the ESLT to the EUN may need to have a whole new
protocol defined, TBD. </font>
<li value=2><font size=3 face="sans-serif">The returned “control report”
from the CFDP agent in the ESLT to the EUN could potentially use an extended
SLE R-OCF service, which already does something very similar for the link
layer control field. This would not need a whole new protocol, just
an adaptation of an existing one. </font>
<li value=3><font size=3 face="sans-serif">The returned “control report”
and return “CFDP agent control” between the CFDP agent in the ESLT and
the EUN could potentially use the new SC-CSTS, which is intended for “service
control”. This would not need a whole new protocol either, but any
such “control report” and “control protocol” would need to be defined.
</font>
<li value=4><font size=3 face="sans-serif">The processing to be done on
the file that is sent to the ESLT from the EUN must either be “defined
by management”, i.e. handled by some out of band, unspecified means, or
have a protocol defined that can deal with the specifics of what the ESLT
must do to take the file, chop it up, create CFDP PDUs (with whichever
of the many CFDP options have been selected by the mission in configuring
CFDP), package it in SPP or EP, create frames of the correct type from
those encapsulated PDUs, merge those frames into the correct virtual channels,
and multiplex them into the frame stream to be encoded and radiated within
the ESLT. </font>
<li value=5><font size=3 face="sans-serif">Note that most of these kinds
of operations, starting with “take the file, chop it up” and ending with
“insert these new frames into the frame stream” are usually done in the
EUN. With this new service these operations must be done in the ESLT,
and thus the ELST must be instructed in just what must be done, in detail.
</font>
<li value=6><font size=3 face="sans-serif">Upon further consideration,
this part sounds a lot like what was defined, in the abstract, as part
of the SISG First Hop / Last Hop service. A couple of presentations
on that, dating from 2010 and 2011, are included for your consideration.
See if what was defined here for sending a file to the “Last Hop”
in a DTN chain, and for managing that process, looks a whole lot like what
you think must be defined for this “forward / return file service”. If
not identical it is surely similar in nature. </font>
<li value=7><font size=3 face="sans-serif">It is worth noting, as well,
that the new CSS Functional Resource Model (FRM) defines a set of “production
processing” building blocks that could, just as easily, be deployed in
a relay spacecraft, or in describing the behavior inside an ESLT running
FF-CSTS and a CFDP agent. This FRM may offer a clean way to define
these behaviors and to extend them as needed for this purpose. This
is to clearly define the processing that must occur within a system element
as opposed to the service interfaces and protocols that appear at the boundaries
of a system element. </font>
<li value=8><font size=3 face="sans-serif">We also briefly discussed the
SOIS Electronic Data Sheets (EDS) at the start of the meeting, and the
relationships, as we understand them, between the EDS and the FRM. This
is obviously a subject that also requires a deeper dive, but it appears
that the strength of the EDS lies in defining the <u>interfaces</u> of
components in a way where these EDS definitions can be used to drive software
development. More on this as we dig into it. The FRM defines
the <u>behavior</u> of those components and how we expect to connect them.</font></ol><font size=3 face="sans-serif">
<br>
As I think you can all see there is some real work to be done if we are
to create a Forward / Return File Service spec that it truly interoperable
and has all these special, and unusual, properties. We do not think
we can do this in the SEA SAWG, this is work that must be done in the other
Areas that “own” the respective sets of standards. At the same
time we see some potential for leveraging work in different areas and integrating
it to provide a more unified end-to-end approach, and that is our express
goal as we try to help sort this out. <br>
<br>
I’ll post a Doodle Poll to see if we can find a mutually agreeable time.
Meanwhile, I’d like to hear from any of you who have opinions, thoughts,
considerations, or cautions that you wish to share. <br>
<br>
Best regards, Peter <br>
<br>
<br>
[attachment "SISG Last Hop delivery v5.2a 25May10.ppt" deleted
by Holger Dreihahn/esoc/ESA] [attachment "SISG ADD NW Mgmt Last Hop
figures v0.2 17Oct11.ppt" deleted by Holger Dreihahn/esoc/ESA] [attachment
"Fig 6-20 Fwd File Svc ESLT & EUN.jpeg" deleted by Holger
Dreihahn/esoc/ESA] [attachment "Fig 7-2 SSI fwd end-to-end.jpeg"
deleted by Holger Dreihahn/esoc/ESA] </font>
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</PRE>