[CESG] [EXTERNAL] AW: Last Hop / First Hop service

Shames, Peter M (US 312B) peter.m.shames at jpl.nasa.gov
Wed May 31 05:22:40 UTC 2023

Hi Tomaso,

I do not think that there is anything in the LunaNet, nor in the IOAG Mars and Lunar comm architectures, that substitutes for this capability.  I think that the focus has most always been on the core functions of DTN, and CPNT, and not on any standardized way to recover from problems.  When we did the SISG report we were initially focused on how we could use this new DTN capability to service end nodes that were not DTN enabled, but also how we could provide a “reboot” capability for an ailing spacecraft from a nearby DTN node.  The capabilities includes in this package were to address that, and we also realized that there were other features that we could layer on this, like open loop recording for EDL tracking.

We associated this with SSI and DTN because the capabilities are only really needed in a DTN context.  That said, I do realize that these features can be viewed as an “application” built on top of DTN and that some group other than SIS DTN WG might be better equipped to define it.  In some ways what is needed is not unlike a specification for a ground station, instructing it to configure for a given purpose and then to radiate data of a stated form in a stated direction.  In some ways this is similar to what CSS SM does, but at a much lower level of detail.  Perhaps CSS FRM has something to contribute.

Or it may be that SOIS EDS could be used to define the formats of these data items and services.  The data themselves, and the meta-data / delivery instructions can, I believe, be sent as a simple file transfer to the “service port” using CFDP and DTN.

I think we need something that is very simple and focused.

Best regards, Peter

From: "Tomaso.deCola at dlr.de" <Tomaso.deCola at dlr.de>
Date: Tuesday, May 30, 2023 at 8:01 AM
To: Peter Shames <peter.m.shames at jpl.nasa.gov>, CESG <cesg at mailman.ccsds.org>
Subject: [EXTERNAL] AW: Last Hop / First Hop service

Hi Peter,

Thank you for providing the report from the SISG dated 2010! I was quite aware of that version but I had did not include the backup slides which also contain some relevant material.

In my opinion, the open points (=questions for CESG) are the following:

  1.  Is this ICPA requirement still meaningful or can it be superseded in favour of any new ones possibly coming from the Lunanet WG within IOAG?
  2.  If still requirement, which area shall lead the corresponding specification work ? According to what stated in the report, it would be about the definition of an delivery agent running on the higher protocol layers (e.g. in top of CFDP/SSI protocol stack) and the specification of the corresponding services

As to point 2), as already stated we see this not SIS-centric, as DTN is concerned here in terms of relaying capabilities but no more than that (at least according to the discussion had in the DTN WG). We are in any case happy to support the activity in whatever area is going to be carried out.

Best Regards,


Von: Shames, Peter M (US 312B) <peter.m.shames at jpl.nasa.gov>
Gesendet: Dienstag, 30. Mai 2023 10:05
An: de Cola, Tomaso <Tomaso.deCola at dlr.de>; CESG <cesg at mailman.ccsds.org>
Betreff: Last Hop / First Hop service

Dear Tomaso, et al,

During today’s CMC meeting the question came up of the origins of the Last Hop / First Hop service.  Regardless of which Area or WG takes this work up, I thought it worthwhile to share the document that defined this service, along with the rationale for it.

This was studied in 2010 as part of the IOAG Space Internetworking Strategy group (SISG).  It was intended as a service to “determine how the SSI will handle services for spacecraft that do not or cannot implement SSI user node functions”.  This explicitly includes SSI nodes that need to be “rebooted” using link layer / emergency commands, as well as nodes that are not DTN nodes, but that could benefit from using a higher speed DTN relay service than their own DTE/DFE link can support.

For the record, the attached document is what was published by the IOAG back in 2010.

Cheers, Peter

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