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[dtn] DTN BPv7 test bundles and CRCs

Brian Sipos <BSipos@rkf-eng.com> Fri, 22 March 2019 15:45 UTC

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From: Brian Sipos <BSipos@rkf-eng.com>
To: "dtn@ietf.org" <dtn@ietf.org>
Thread-Topic: DTN BPv7 test bundles and CRCs
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Date: Fri, 22 Mar 2019 15:45:14 +0000
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Subject: [dtn] DTN BPv7 test bundles and CRCs
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To anyone who has been prototyping Bundle Protocol version 7 (BPbis) agents,
I'm spending a little time on a Wireshark dissector to examine and troubleshoot bundles and the only trouble I've run into is in verifying the CRCs. The BPbis spec is not very helpful in determining exactly what CRC implementation to use only because the ITU specification itself doesn't provide CRC test vectors.

I'm doing prototyping in Python and dissecting in C language, so there is even a disparity between what CRC algorithms are available and how well they are documented. This seems like such an easy use/build decision to use COTS CRC function but I'm struggling to find implementations to match what BPbis requires.

I think there would be a lot of value to have some test/representative bundles in an appendix which include blocks with different CRC types and different block sizes. Some CRC implementations pad out octet-sequences to a multiple of the CRC size and some apparently do something else. The problem is in the CRC implementations not being very clear about their parameters but having a few encoded test bundles to work with would go a long way to ensuring compatibility of implementations.

Thanks for any advice,
Brian S.

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