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

[Gian.Paolo.Calzolari at esa.int]

Adrian, 
        I noticed the comments by Keith Scott and I already wrote to Greg 
to comment about which comments can be solved at once and which one should 
be converted to RIDs (author SLP WG Chair on behalf of Keith I would 
propose) for discussion within Agency Review.

For the very first comment,  it looks as they do not in conflict as there 
is guarantee within a session but not across session. It may be this 
should be highlighted somehow in section 2 too.

For sure you will get SLS position soon but I propose not delaying the CMC 
poll for this.

Regards

Gian Paolo



From:
"Hooke, Adrian J (9000)" <adrian.j.hooke at jpl.nasa.gov>
To:
CCSDS Secretariat <tomg at aiaa.org>, CESG <cesg at mailman.ccsds.org>, "Kazz, 
Greg J (313B)" <greg.j.kazz at jpl.nasa.gov>
Date:
28/02/2012 15:43
Subject:
[CESG] RE: Results of CESG poll - Proximity-1 Space Link Protocol-Data 
Link Layer
Sent by:
cesg-bounces at mailman.ccsds.org



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.
 
------
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)?
----
 
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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