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

[Kazz, Greg (US 312B)]

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.
[cid348906*image003.png at 01D86530.39956FC0]

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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