[Css-csts] inaccurate references to FTCF SLE service in FSP specification

[John Pietras]

CSTSWG colleagues ---

 

The Forward Space Packet (FSP) Pink Book (soon to be Blue-2) makes
numerous statements about being carried by an underlying Forward
Telecommand Frame (FTCF) SLE service. While in a formal sense this is a
possible configuration (it is the one that is illustrated in the Cross
Support Reference Model - Part 1 - SLE Services (often simply referred
to as the SLE-RM), it is not necessary to have an underlying FTCF SLE
service and in fact it cannot be so, since we have operational FSP
services without having specified the FTCF service! This inconsistency
was brought to my attention by Peter Shames, who asked how it could be
possible to operate the FSP over a non-existent SLE service.

 

In fact, all that is necessary for the FSP SLE service to work is to
have the *production processing* associated with the FTCF service and
the FCLTU service. The only time that explicit FTCF and/or FCLTU
services are needed "beneath" the FSP service is if the FSP service is
"staged" across two or more Service Complexes, e.g., 

1.	MDOS (FSP user) -> (intermediate) Complex A (FSP provider/MAP/
TC frame generation/FOP/FTCF User) -> Complex B (FTCF provider/CLTU
generation/PLOP/RF & Mod);
2.	MDOS (FSP user) -> (intermediate) Complex C (FSP provider/ MAP/
TC frame generation/ FOP/ CLTU generation/ FCLTU User) -> Complex D
(FCLTU provider/ PLOP/RF & Mod);
3.	MDOS (FSP user) -> (intermediate) Complex E (FSP provider/MAP/
TC frame generation/FOP/FTCF User) -> (intermediate) Complex F (FTCF
provider/CLTU generation/ FCLTU User) -> 
	Complex G (FCLTU provider/ PLOP/RF & Mod)

 

Indeed, it is my understanding that at least some of the FSP
configurations are directly provided by the ground station:

     MDOS (FSP user) -> Complex X (FSP provider/MAP/TC frame
generation/FOP/CLTU generation/PLOP/RF & Mod)

 

Perhaps when the references to underlying FTCF SLE service were first
written, it was expected to have an FCTF SLE service specification
available shortly after. However, given that this is not the case, it is
currently incorrect to state that the FSP service relies on the
existence of the FTCF service. Even if and when the FTCF service *is*
specified, in would still be inaccurate to imply that the FSP service
must run in conjunction wit FTCF (and FCLTU) SLE service.

 

It is unfortunate that we didn't discover this sooner, in time at be
folded into the current Pink Book.  Is there anything that we can (and
want to) do about this in the near term? Is it worth exploring what
changes would be necessary to make the FSP book technically correct,
even if the changes cannot be folded into the upcoming Blue-2 version?

 

Best wishes for the holidays,

John

 

John Pietras

GST, Inc. 

7855 Walker Drive, Suite 200

Greenbelt, MD 20770

240-542-1155

 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mailman.ccsds.org/pipermail/css-csts/attachments/20091221/b0221fb6/attachment.html