[Css-csts] Propose SpaceLinkDatUnit lower bound be set to 1

[Timothy Ray]

John,

What you said makes very good sense to me.

Tim 


----- Original Message ----- 
From: "John Pietras" <john.pietras at gst.com>
To: <css-csts at mailman.ccsds.org>
Cc: "Fred Brosi" <brosi at gst.com>
Sent: Friday, May 20, 2005 2:50 PM
Subject: [Css-csts] Propose SpaceLinkDatUnit lower bound be set to 1


> Members of the CSTS WG,
> Last week I identified a discrepancy between the minimum size of the
> SpaceLinkDataUnit type definition in the CLTU Blue Book-2 and the rest
> of the Blue Books (see below).
> 
> I would like to propose that in the next revisions, the minimum size be
> set to 1. This request is the result of a practical concern that I have
> come across in trying to apply the CLTU service to our admittedly
> non-CCSDS-standard application, but I think that the current
> greater-than-one minimum size might arise as a more general problem.
> 
> As I understand it, the minimum size has been set to the smallest
> possible size of the any of the CCSDS space link data units (as defined
> in the reference model) that are moved by an SLE transfer service. When
> only the RAF and CLTU services were being developed, the minimum size
> was 7 octets, driven by the smallest possible telemetry frame. The
> minimum size is now 4 octets, because the OCF field is 4 octets. 
> 
> Clearly, data type-specific processing is not depending on SLE to
> enforce SLDU sizes, since the common SpaceLinkDataUnit allows too-small
> (by CCSDS standards) "telemetry frames" and "CLTUs", and too-large OCF
> fields (up to 64k). In all cases the legal size for any specific data
> type must be enforced by application-level processes. 
> 
> There seems to be little advantage to requiring SLE to enforce a minimum
> size that is specific to only one CCSDS SLDU (the OCF), and a potential
> disadvantage for non-standard uses that transfer smaller data units.
> Setting the minimum size to 1 would not diminish, SLE and it might allow
> more potential uses of SLE transfer services. 
> 
> Thank you in advance for considering this proposal.
> 
> Best regards,
> John
> 
> > -----Original Message-----
> > From: John Pietras
> > Sent: Thursday, May 12, 2005 4:58 PM
> > To: css-csts at mailman.ccsds.org
> > Subject: Discrepancy in SpaceLinkDatUnit lower bound
> > 
> > Members of the CSTS WG,
> > Perhaps this is something that has already been recognized, but I will
> > raise it in case it has so far otherwise escaped detection.
> > 
> > There is a discrepancy in the lower bound of the SpaceLinkDataUnit
> type
> > definition in the various sections A2.1 SLE TRANSFER SERVICE--COMMON
> > TYPES:
> > - In RAF-B-2, RCF-B-1, FSP-B-1, and ROCF-B-1, the lower bound is 4.
> > - In CLTU-B-2, it is 7 (it was also 7 in both RAF-B-1 and CLTU-B-1).
> > 
> > I assume that the value was lowered to accommodate ROCF, but that the
> > change failed to be reflected in CLTU-B-2.
> > 
> > Best regards,
> > John
> 
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