[SIS-CFDPV1] revised draft specification
Felix.Flentge at esa.int
Felix.Flentge at esa.int
Wed Dec 11 08:25:52 UTC 2019
Hmmh,
I wouldn't like to introduce too much change in the draft at the current
stage.
In general, I think:
1) We could have checksum ID for private / experimental use but its use
should be discouraged.
2) Implementations may or may not support private / experimental checksums
(or be configurable). This could go to the MIB but does not have to (as
for the other checksum ID). It's an implementation matter.
3) If an implementation chooses to support private / experimental
checksums, it will try to apply a checksum which may either succeed or
fail. Which exact checksum to apply is again an implementation matter,
could be per source or generic or guessing based on some other information
...
4) If an implementation chooses not to support private / experimental
checksums, it will raise the Unsupported Checksum Type fault.
For the interoperability testing, I am not sure how much of this has to be
covered. As the private / experimental checksum is, well
'private/experimental', I don't think we have to test something for the
standard interoperability. Dealing with unsupported checksums seems also
more a 'local' entity issue and not so much required for interoperability
testing.
Regards,
Felix
From: <Jeremy.Mayer at dlr.de>
To: <chkoo at kari.re.kr>, <Felix.Flentge at esa.int>,
<sis-cfdpv1 at mailman.ccsds.org>, <sis-cfdpv1-bounces at mailman.ccsds.org>
Date: 11/12/2019 08:49
Subject: Re: [SIS-CFDPV1] revised draft specification
Hi Cheol,
Understood, and to respond to both of your emails at once: I think that
the "private/experimental" checksum ID will cover this scenario, without
requiring the allocation of the limited range of checksum ID's which are
supported by CFDP.
To use your example, if the sending entity uses a private checksum
algorithm, then they would put checksum ID private_use (whichever ID that
may be) into the metadata PDU. Upon receiving that checksum, the receiving
entity MUST search the MIB in order to determine which checksum is used
for that source CFDP entity ID, and process accordingly. If it doesn't
find a checksum, then the "Unsupported Checksum Type" error is raised.
This would still increase the complexity of the MIB and checksum
processing pipeline, but we can outline that the private_use checksum ID
MUST search the MIB to determine the actual checksum algorithm, and shall
fail if more or less than 1 checksum matches for a given CFDP source
entity ID.
Thanks,
Jeremy
From: 구철회 <chkoo at kari.re.kr>
Sent: Wednesday, December 11, 2019 8:46:23 AM
To: Mayer, Jeremy; Felix.Flentge at esa.int; sis-cfdpv1 at mailman.ccsds.org;
sis-cfdpv1-bounces at mailman.ccsds.org
Subject: RE: [SIS-CFDPV1] revised draft specification
Hi, Felix.
If we choose one ID as 'Reserved for Private and/or Experimental Use, that
means a CFDP implementation can support the ID; therefore when the ID is
applied to a filestore request, a receiving entity (who can handle the ID)
will have no problem to process the request. No fault condition can be
issued.
Jeremy’s idea can handle the situation. But a ‘prior coordination
between agencies’ should be made before entering a real testing in order
to know which one is an implemented checksum algorithm (because the
sending entity have to process a file delivery request), or a fake
algorithm (non-support algorithm). I think that could be not what we want
in this context.
Cheol
From: Jeremy.Mayer at dlr.de <Jeremy.Mayer at dlr.de>
Sent: Wednesday, December 11, 2019 4:17 PM
To: Felix.Flentge at esa.int; 구철회 <chkoo at kari.re.kr>;
sis-cfdpv1 at mailman.ccsds.org; sis-cfdpv1-bounces at mailman.ccsds.org
Subject: Re: [SIS-CFDPV1] revised draft specification
Felix,
I agree. Checksum ID's 0-15 are reserved for CFDP, so that checksum can
be added to the blue book without altering the registry. However, it may
make sense to allocate two checksum ID's for general (non-CFDP specific)
use: one for private and one for experimental.
If we did that, checksums 0-3 would be "real" checksums, 4-12 would be
reserved for CFDP, 13 & 14 would be private/experimental, and 15 would
NULL.
Thanks,
Jeremy
From: Felix.Flentge at esa.int <Felix.Flentge at esa.int>
Sent: Wednesday, December 11, 2019 8:10:41 AM
To: chkoo at kari.re.kr; sis-cfdpv1 at mailman.ccsds.org; SIS-CFDPV1; Mayer,
Jeremy
Subject: Re: [SIS-CFDPV1] revised draft specification
Dear All,
I would support that idea. We could be even more general (also to avoid
changing the current draft standard wrt to the MIB) to just have one ID
specified as 'Reserved for Private and/or Experimental Use'.
Regards,
Felix
From: <Jeremy.Mayer at dlr.de>
To: <chkoo at kari.re.kr>, <sis-cfdpv1 at mailman.ccsds.org>
Date: 11/12/2019 08:01
Subject: Re: [SIS-CFDPV1] revised draft specification
Sent by: "SIS-CFDPV1" <sis-cfdpv1-bounces at mailman.ccsds.org>
Hi Cheol,
I can answer your questions about the Checksum registry: First, I'm not
sure why the checksum ID's are non-sequential, since I'm not sure what the
SANA website is sorting by, but if you click the "ChecksumID" column
header, it should sort correctly.
I would suggest that, in the scenario which you outlined, the MIB
containing the supported checksums for a receiving entity should be
updated via TC and/or the desired checksum should be sent during a
filestore request, but that's a more impactful change. I am adverse to a
one-to-one allocation of checksum ID's to agencies, since it ultimately
negates the purpose of the checksum ID and complicates mission operations
and cross support: a single receiving CFDP entity at a ground station can
(and likely will) support multiple missions, some of which may be
performed from different agencies, each of which may have their own
checksumming capabilities and requirements. If a single checksum ID is
allocated to each agency, the receiving entity will be unable to determine
the "real" checksum in use, unless that data is conveyed via some
out-of-band mechanism.
Additionally, different files from a single mission may require different
checksums, either due to bandwidth constraints, mission phase, and/or
avionics capabilities, meaning that the receiving entity will have to be
aware of the mapping between entities, sessions, and checksum
configurations. This is further complicated by the rise of file-based
operations and advanced FDIR systems: it may be possible for the sending
entity to change checksum modes in the event of a failure, in order in
order to reduce power utilization and/or computational complexity.
What would be possible is to allocate a single checksum ID to be "MIB
defined". If that ID is in use, then it's up to the sender/receiver to
determine the checksum out-of-band, but I think that would require some
changes to the blue book.
Thanks,
Jeremy
From: SIS-CFDPV1 <sis-cfdpv1-bounces at mailman.ccsds.org> on behalf of 구철
회 <chkoo at kari.re.kr>
Sent: Wednesday, December 11, 2019 1:48:18 AM
To: sis-cfdpv1 at mailman.ccsds.org
Subject: Re: [SIS-CFDPV1] revised draft specification
Hi, Scott.
I like your idea. I am currently working on the modification of CFDP
software from my side, and I love to perform the supplementary
interoperability test when the updated ION and interoperability test plan
are available.
I don’t see many testing items are required for this supplementary
testing. However as I sent it earlier to you there is a tricky issue with
regard to handling condition code of ‘Unsupported checksum type(1011)’.
In order to make that situation, the ‘Unsupported checksum type’ is
generated, happen, a CFDP (sending) entity should be able to generate a
checksum field by a checksum algorithm that the other CFDP (receiving)
entity does not support. As there are not much choices in selection of
checksum algorithms, it can be tricky because one CFDP entity may have to
implement an unnecessary checksum algorithm that is even not consistent
with CFDP Checksum Identifiers in SANA registry (
https://sanaregistry.org/r/checksum_identifiers).
* short question : why are the number of the checksum ID in the SANA
not consistently sequential? E.g., 4,5,(6?),7,(8?),9,10,11,12,13,14,6,8
,15.
After thinking about this issue, I like to propose an idea. Why don’t we
allocate a Checksum ID to each space agencies, e.g., KARI reserve 5 as a
checksum ID for potential use. Then KARI can freely choose the checksum
algorithm for checksum ID 5, e.g., just a copy of modular, CRC32 or
whatever or in-house algorithm for sure. When KARI put the 5 at the
checksum type field in Metadata PDU, with all the interoperability testing
with space agencies, the ‘Unsupported checksum type’ condition code
should be designated at the FIN PDU from a receiving CFDP entity since all
space agencies except KARI doesn’t have any reference for the checksum ID
of 5. How do you think?
Cheol
From: SIS-CFDPV1 <sis-cfdpv1-bounces at mailman.ccsds.org> On Behalf Of
Burleigh, Scott C (US 312B) via SIS-CFDPV1
Sent: Wednesday, December 11, 2019 1:21 AM
To: sis-cfdpv1 at mailman.ccsds.org
Subject: [SIS-CFDPV1] revised draft specification
Hi, all. Following some additional discussion of the RID dispositions
proposed in the Darmstadt meeting, we now have got a final (I hope) draft
specification posted to CWE at
https://cwe.ccsds.org/sis/docs/SIS-CFDPV1/Draft%20Documents/727x0b5%20--%20Specification%20--%20Blue%20Book/727x0p42_working%204.doc?Web=1
; PDF is at
https://cwe.ccsds.org/sis/docs/SIS-CFDPV1/Draft%20Documents/727x0b5%20--%20Specification%20--%20Blue%20Book/727x0p42_working%204.pdf
.
This draft has gone to the Secretariat for final editing, but the
technical stuff won’t be changing unless we discover a problem in
interoperability testing.
Speaking of which, I hope to do that (small, supplementary)
interoperability test in January. Cheol and Chenyunjun, please take one
more look at the markups in the revised spec to make sure the final tweaks
are reflected in your code? I need to modify ION’s CFDP as well and hope
to have that done in early January. We’ve discussed a plan for this
supplementary testing, and we should try to tie off that discussion and
finalize the plan sometime in the next couple of weeks. (Holidays in the
U.S. will complicate this, but it should still be doable.)
The end is in sight, I swear.
Scott
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