[Sis-dtn] BPv7/LTP binding issues

[Sipos, Brian J.]

All,

I hadn't looked into the convergence layers section of the draft BPv7 blue
book [1] earlier, and understand that these comments are coming late in the
draft process.

 

The requirements in Section B2.1.4 "LTP Convergence Layer Adapter" currently
don't actually specify which LTP Client Service ID is to be used for this
CLA and because this "multiple bundles within a block" encoding scheme is
different than what is defined for Client Service code point 1, I think that
a new Client Service code point needs to be allocated for this encoding. It
would also be valuable for a decoder to understand whether this encoding
form allows only BPv7 bundles to be present or also v6 (or even a mix of the
two). These are all considerations that if left unspecified will lead to
interoperability failures.

 

Separate from the Client Service ID, the notion of a "length prefixed set of
bytes" within CBOR is actually how the byte string major type [4] operates
and this encoding seems like it would be better understood by encoders and
decoders as a byte string type. In fact, this pattern of
CBOR-within-byte-string is common enough that there is both CDDL schema for
it as well as CBOR diagnostic notation for it. This second comment is less
of an interoperability issue and more of a way to stick to existing tooling
conventions for handling bstr-embedded CBOR.

 

The CDDL for this would be something like:

bp-in-block = (+bundle-bytes) ; encoded as a CBOR sequence

bundle-bytes = bstr .cbor bundle

; where "bundle" symbol is from Appendix B of RFC 9171

 

and the diagnostic notation is to enclose items with "<<" and ">>" brackets
[5].

 

Thanks for any consideration,

Brian S.

 

[1] https://public.ccsds.org/review/CCSDS%20734.2-P-1.1/734x2p11e1.pdf

[2]
https://www.iana.org/assignments/ltp-parameters/ltp-parameters.xhtml#client-
service-ids

[3] https://sanaregistry.org/r/ltp_serviceid/

[4] https://www.rfc-editor.org/rfc/rfc8949.html#section-3.1-2.5

[5] https://www.rfc-editor.org/rfc/rfc8610#appendix-G.3

 

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