[CESG] RE: Results of CESG poll - Proximity-1 Space Link Protocol-Data Link Layer

[Hooke, Adrian J (9000)]

RE: CESG-P-2012-02-002 Approval to release CCSDS 211.0-P-4.1,  Proximity-1 Space Link Protocol-Data Link Layer (Pink Book, Issue 4.1) for CCSDS Agency review Results of CESG poll beginning 13 February 2012 and ending 27 February 2012:



I note a large number of comments from Keith Scott under the category "Approve Unconditionally". Some of these - particularly the ambiguities about duplicate data that are highlighted below - seem to be fundamental technical issues  that should be resolved before inflicting the document on Agency review?

Keith, Greg - comments?



2.2.3.2

How do we reconcile 2.2.3.2:

The Sequence Controlled service ensures that data are reliably transferred across the space link and delivered in order, without gaps, errors, or duplications within a single communication session without COP-P resynchronization during the session (see 4.3.2).



with Note 2 in section 4.3.2.2:

2 The mechanisms provided in this specification will not eliminate duplicate data associated with the transition between the end of one session and the beginning of the next. Elimination of this problem is left to the controlling data system.



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2.2.3.2

I think where it says: "...without gaps, errors, or duplications wthin a single communication session *without COP-P resynchronization during the session*..."?



might be better phrased as:

"... without gaps, errors, or duplications within a single communication session *when COP-P resynchronization is not required during the session (see 4.3.2).*"



AND it seems like there may be duplicates anyway if there are other sessions (as above)?

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4.3.2.2 (and Reliable Data Transfer in general) Is the user informed of whether COP-P resynchronization has taken place during the course of a single communication session?  If not, how does the receiver know if there may be duplicate data?  Does detecting resynchronization require setting the MIB parameter Resync_Local to 'false'?  If the user is required to monitor the RESYNC variable (7.1.2) to detect resynchronization, is there any guarantee that the user will detect the change (that is, if the user reads 1/second, will they notice the resynch event?)



Note 1 in section 4.3.2.2 -- how is the delivery of duplicate data due to factors outside the scope of the Proximity-1 protocol?  It seems that duplicate data may be delivered because the

Proximity-1 protocol does not detect duplication across resynchronization events, but I suspect a more robust COP-like protocol *could*.  The point is, the duplicate data is a result of the Prox-1 reliability mechanisms not being robust across resynchronzation, not some sort of external factor.



What are the 'bounds' on duplicate data reception associated with Note 2 in section 4.3.2.2?  Are all data received with 256 frames of a communication session boundary suspect of duplication, e.g.?



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