[Sis-dtn] [EXTERNAL] RE: Special use of sequence number in bundle creation time stamp

Wed Aug 9 15:49:56 UTC 2023

Hi, Jonathan.  I haven't thought through this in depth, but off the top of
my head I would cite Felix's remark that "In case 10 with different
destination endpoint IDs, the BPA has to guarantee that the same values can
only appear with different bundle creation times!"  If the spacecraft has no
accurate clock then the bundle creation time will always be zero, so this
case apparently can't be supported.  With a little imagination I suspect we
can think of other cases that will also be problematic.

The processing of bundle primary blocks is already complex.  I don't think
it's advisable to make it any more complicated than it already is.

Scott

From: Wilmot, Jonathan J. (GSFC-580.0)[VANTAGE SYSTEMS INC]
<jonathan.j.wilmot at nasa.gov> 
Sent: Wednesday, August 9, 2023 8:43 AM
To: sburleig.sb at gmail.com
Cc: Singh, Somendra {Simon} (GSFC-5820) <simon.singh at nasa.gov>; 'Felix
Flentge' <Felix.Flentge at esa.int>; 'Dr. Keith L Scott via SIS-DTN'
<sis-dtn at mailman.ccsds.org>
Subject: RE: [EXTERNAL] RE: [Sis-dtn] Special use of sequence number in
bundle creation time stamp

Scott,

   I am not seeing how it makes the original use case more difficult. The
timestamp is still time and a sequence number in context of a given source
EID. It may help the original use case for systems that are having time
issues.  

   I may be missing something, could you please add more detail on the
issue(s)?

Kind regards,

     Jonathan Wilmot

CCSDS SOIS Area Director

GSFC DTN Systems Engineer

cFS Architecture

Cell 301-751-2658

From: sburleig.sb at gmail.com <mailto:sburleig.sb at gmail.com>
<sburleig.sb at gmail.com <mailto:sburleig.sb at gmail.com> > 
Sent: Wednesday, August 9, 2023 11:31 AM
To: 'Felix Flentge' <Felix.Flentge at esa.int <mailto:Felix.Flentge at esa.int> >;
'Dr. Keith L Scott via SIS-DTN' <sis-dtn at mailman.ccsds.org
<mailto:sis-dtn at mailman.ccsds.org> >
Cc: Singh, Somendra {Simon} (GSFC-5820) <simon.singh at nasa.gov
<mailto:simon.singh at nasa.gov> >; Wilmot, Jonathan J. (GSFC-580.0)[VANTAGE
SYSTEMS INC] <jonathan.j.wilmot at nasa.gov <mailto:jonathan.j.wilmot at nasa.gov>
>
Subject: [EXTERNAL] RE: [Sis-dtn] Special use of sequence number in bundle
creation time stamp

CAUTION: This email originated from outside of NASA.  Please take care when
clicking links or opening attachments.  Use the "Report Message" button to
report suspicious messages to the NASA SOC. 

Hi, Felix.  One thing to keep in mind is that the purpose of the sequence
number in the bundle creation timestamp is to distinguish among bundles that
have the same bundle creation time.  This can occur when bundles are created
at a very high rate or when bundle creation time is zero due to the absence
of an accurate clock.

I would suggest that using bundle creation timestamp sequence numbers for
other purposes makes it more difficult to use those numbers for their
original purpose.

If sequence numbering of bundles in these various ways is important, I think
it would be better to encode those numbers (and the flags describing their
significance) in an immutable extension block, i.e., an extension block that
is one of the additional targets of a block integrity block covering the
primary block.

Scott

From: SIS-DTN <sis-dtn-bounces at mailman.ccsds.org
<mailto:sis-dtn-bounces at mailman.ccsds.org> > On Behalf Of Felix Flentge via
SIS-DTN
Sent: Wednesday, August 9, 2023 7:43 AM
To: Dr. Keith L Scott via SIS-DTN <sis-dtn at mailman.ccsds.org
<mailto:sis-dtn at mailman.ccsds.org> >
Cc: Singh, Somendra {Simon} (GSFC-5820) <simon.singh at nasa.gov
<mailto:simon.singh at nasa.gov> >; Wilmot, Jonathan J. (GSFC-580.0)[VANTAGE
SYSTEMS INC] <jonathan.j.wilmot at nasa.gov <mailto:jonathan.j.wilmot at nasa.gov>
>
Subject: [Sis-dtn] Special use of sequence number in bundle creation time
stamp

Dear All,

I think we have had some initial exchange on the use of the sequence number
in the bundle creation timestamp some time ago. Meanwhile, we had a number
of side meetings with Jonathan, Simon and others to further discuss the
topic of 'flows', compressed bundle reporting and network management.

We have arrived at a point where we think that it makes sense to allow using
the sequence number in the primary header for identifying gaps in sequences
of bundles or to even allow for in-sequence delivery.

The basic idea is that the sequence number does not get reset to zero but is
incrementing by one until a specified maximum. Further we might use
different, individual sequence numbers per source node ID or per destination
endpoint ID. Such a behaviour might be governed by policy or even indicated
in the Primary Block's Processing Control Flags, like

1.	Use two bits to specify whether the creation timestamp sequence
number is used in special way:

*	00 - single sequence number - no specific usage
*	01 - an individual sequence number is used per source node id
*	10 - an individual sequence number is used per destination endpoint
id
*	11 - reserved (until we find a good usage; maybe individual sequence
number per next hop)

In case 10 with different destination endpoint IDs, the BPA has to guarantee
that the same values can only appear with different bundle creation times!

2.	Use of two bits to indicate the maximum length of the sequence
number (00 above) or individual sequence numbers (01 and 10 above):

*	00 - sequence numbers are assigned somehow (reset to zero, randomly,
..)
*	01 - increasing sequence number up to 2^16-1
*	10 - increasing sequence number up to 2^32-1
*	11 - increasing sequence number up to 2^64-1

My main questions:

1.	Does it make sense to use flags in the primary header for this
purpose or is it sufficient to document that sequence numbers can be used in
that way and leave it up to policy to specify certain behaviours? I have a
slight preference for using the BPCF as it seems more formal and could ease
interoperability (and the sequence number is in the primary header, so why
not indicate it there).
2.	If we want to use BPCF, what is the way to specify this? Should we /
do we need to go IETF or could CCSDS be sufficient (to start with)? Ideally
we would use some of the reserved first 16 bits (e.g. Bit 7 - 10)
3.	No matter whether we want to use BCPF or not, I think something
should end up in the CCSDS BB as soon as possible. So, maybe there is a
chance for a late RID (if it does not delay the overall publication
process). We should start discussing (maybe tomorrow).

Regards,

Felix

This message is intended only for the recipient(s) named above. It may
contain proprietary information and/or protected content. Any unauthorised
disclosure, use, retention or dissemination is prohibited. If you have
received this e-mail in error, please notify the sender immediately. ESA
applies appropriate organisational measures to protect personal data, in
case of data privacy queries, please contact the ESA Data Protection Officer
(dpo at esa.int <mailto:dpo at esa.int> ). 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.ccsds.org/pipermail/sis-dtn/attachments/20230809/f920cee9/attachment-0001.htm>