[Sls-slp] Extending the 1st Header Pointer in AOS to 16 bits to cover max Transfer Frame length

[Marco.Rovatti at esa.int]

Good morning SLP-WG, 

Being the AOS Frame length a managed parameter and therefore mission 
dependent, its extension to max 65536 octets does not make existing assets 
incompatible. In fact, new missions wishing to re-use recurrent HW/SW, may 
still decide to keep on using 2048 octets long AOS Frames. 
If max AOS Frame length gets extended, I'd rather go for expanding the 1st 
header pointer to 16 bit if CCSDS Space Packet Protocol than constraining 
the max packet length. 
In fact, I would discourage restricting max CCSDS packet length as this 
may introduce a severe and unnecessary protocol overhead in systems using 
e.g. CFDP over AOS.

I hope this helps

Best regards

Marco Rovatti
Data Handling and Avionics Engineer

 
P:      +31 71 5655641
A:      Keplerlaan 1, 2201AG, Noordwijk, NL
W:      www.esa.int








From:   "Kazz, Greg\(US 312B\) via SLS-SLP" <sls-slp at mailman.ccsds.org>
To:     "Kazz, Greg (US 312B) via SLS-SLP" <sls-slp at mailman.ccsds.org>
Cc:     "Andrea.Modenini at esa.int" <Andrea.Modenini at esa.int>, "Sank, Victor 
J.\(GSFC-567.0\)\[SCIENCE SYSTEMS AND APPLICATIONS INC\]" 
<victor.j.sank at nasa.gov>, "Rodriguez, Shannon\(GSFC-5670\)" 
<shannon.rodriguez-1 at nasa.gov>
Date:   11/05/2022 19:39
Subject:        [Sls-slp] Extending the 1st Header Pointer in AOS to 16 
bits to cover max Transfer Frame length
Sent by:        "SLS-SLP" <sls-slp-bounces at mailman.ccsds.org>



Dear SLP WG,
 
I’ve been asked by Andrea Modenini, the chair of the C&S WG, to poll you 
concerning their proposal below to utilize the 5 reserve bits in the M_PDU 
header of the AOS Transfer Frame in order to extend the 1st Header Pointer 
from 11 bits (2048 octet Maximum AOS Transfer Frame Size) to 16 bits 
(65536 octet maximum AOS transfer frame). Note: USLP transfer frame 
maximum is also 65536 octets.
 
Please provide me with your opinion by end of day May 17. 
 
Here is the proposal from Victor Sank and Shannon Rodriguez at NASA/GSFC:
 
We agree that First Header Pointer must be able to point to first packet 
header that is in the Packet Zone of the transfer frame.  Even through the 
packets can be very long,  limited to a length of 65536 octets, and may 
cover several transfer frames, the problem is where in the frame the next 
packet starts.  The 11 bit first header pointer is the limitation since it 
would not be able to point far into the frame.  But there are 5 bits of 
reserved that can be used with the 11 bit, giving 16 total and covering 
what we need. 
              We would have to couple the extension of transfer frame 
lengths with making use of the reserved 5 bit in the M_PDU Header.  There 
is also an option that can be used.  If there is objection to extending 
the first header pointer to 16 bits, we could still allow longer transfer 
frames with the restriction that the packets used with these transfer 
frames are (temporarily) limited to 2048 octets.  In the future if/when 
CCSDS agrees to the 16 bit first header pointer, the restriction would be 
removed. 
 
CCSDS732.0-B-3 shows an M_PDU Header with the first header pointer as 11 
bits but also shows 5 bits of reserved.  If we use the 5 bit we have 16 
and can point to 65536. 

 
Best regards,
Chair SLP WG
 
Greg Kazz
Principal Engineer
Technical Group Supervisor,
312B Project Protection, Project Software, and End to End Information 
System Engineering
Jet Propulsion Laboratory
4800 Oak Grove Dr., M/S 301-490
Pasadena, CA 91109
1+(818)393 6529(voice)
1+(818)393 6871(fax)
email: greg.j.kazz at jpl.nasa.gov 
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