[Sis-dtn] [EXTERNAL] AW: practical size of the TC frame

Tue Mar 21 15:17:52 UTC 2023

Thanks Tomaso.

Just to mention that CCSDS SLP WG is working at this coming Spring meeting in May 2023 in Huntsville, AL, USA, for USLP to ease the constraint of 1 TC frame per CLTU to ‘1 or more’ similar to the TC Space Data Link Protocol.

Regards,
Greg

From: "Tomaso.deCola at dlr.de" <Tomaso.deCola at dlr.de>
Date: Tuesday, March 21, 2023 at 3:38 AM
To: "Sanchez Net, Marc (US 332H)" <marc.sanchez.net at jpl.nasa.gov>, "Jim.Bardgett at L3Harris.com" <Jim.Bardgett at L3Harris.com>
Cc: "sis-dtn at mailman.ccsds.org" <sis-dtn at mailman.ccsds.org>, "Kazz, Greg (US 312B)" <greg.j.kazz at jpl.nasa.gov>
Subject: [EXTERNAL] AW: practical size of the TC frame

Hi Marc, Hi Jim,

Just a few additional bits to the discussion. The latest version of the TC C&S book (https://public.ccsds.org/Pubs/231x0b4e0.pdf) now also includes the LDPC. See also below:
[cid:image001.jpg at 01D95BCD.A1A1A950]
Moreover, with the advent of USLP (https://public.ccsds.org/Pubs/732x1b2.pdf) longer frames are now allowed, up to roughly 64kbytes in size. Moreover, the USLP green book (https://public.ccsds.org/Pubs/700x1g1.pdf) also states that:
Furthermore, although there is a maximum transfer frame length limitation due to the Frame Length field for TC in reference [9], the Telecommand Synchronization and Channel Coding specification (reference [11]) allows multiple transfer frames within a Communications Link Transmission Unit (CLTU), so in principle, there is no frame number limitation; however, USLP (reference [3]) allows only one frame.

I’m also cc’ing Greg who can provide some more details.

Hope it can help somehow

Regards,

Tomaso

Von: SIS-DTN <sis-dtn-bounces at mailman.ccsds.org> Im Auftrag von Sanchez Net, Marc (US 332H) via SIS-DTN
Gesendet: Montag, 20. März 2023 19:59
An: Jim.Bardgett at L3Harris.com; Sis-dtn at mailman.ccsds.org
Betreff: Re: [Sis-dtn] practical size of the TC frame

Hi Jim,

Some answers below in blue.

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Marc Sanchez Net (332H)
Telecommunications Engineer
Jet Propulsion Laboratory
Cell: (617) 953-7977<mailto:(617)%20953-7977> | Email: marc.sanchez.net at jpl.nasa.gov<mailto:marc.sanchez.net at jpl.nasa.gov>
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From: SIS-DTN <sis-dtn-bounces at mailman.ccsds.org<mailto:sis-dtn-bounces at mailman.ccsds.org>> On Behalf Of Jim.Bardgett--- via SIS-DTN
Sent: Monday, February 27, 2023 5:03 AM
To: Sis-dtn at mailman.ccsds.org<mailto:Sis-dtn at mailman.ccsds.org>
Subject: [EXTERNAL] [Sis-dtn] practical size of the TC frame

Hoping someone can point me in the right direction on this one. I’m assisting a colleague and we have questions about the frame size limitation:

  *   Upper TC frame size is 1019.  Is the size fixed to 1019? Can it be larger and what would the implications be?
The max size of a TC frame including header is 1024 bits. I believe this is due to the limited num. of bits in the header to encode the length of the transfer frame.
[cid:image002.jpg at 01D95BCD.A1A1A950]

  *   Lower TC Sync Ch Coding CLTU
Each TC frame must fit in one CLTU. Therefore, if using coding, you must fit the number of bits in a TC frame in an integer number of codewords at the Sync & Coding layer. For example, if using BCH (64,56) and a TC frame of 1024 bits, each CLTU will have ceil(1024/56)=19 BCH codewords, the last of which will have padding bits.

  *   Is there a size limitation for Lower TC protocol CLTU?
On the lower end, you need at least one codeword per CLTU, so depending on which code you use, the limitation will vary. For BCH (64,56), the min size of CLTU is 144 symbols, 16 for the start sequence, 64 for the BCH codeword (i.e., 1 BCH codeword), and 64 more for the tail sequence.
The upper limit on the CLTU size is given by the max TC frame size. Another factor is to ensure that the receiver maintains lock when start sequences (which act as sync markers) are increasingly further apart, which depends on SNR conditions, etc.

  *   In at least one document it says:

  *   TC transfer frame between the CLTU start/tail sequences has a max length of 1024 bytes

I’m believing these are the right references for my question. Is that in error?

Thanks and kind regards,

Jim Bardgett
Sr. Manager Cyber – Networks | Ch. Technologist Ntwk Engn
MS Digital Forensics, BSE Electrical, CISSP, CEH, JNCIS-ENT/SEC

Space and airborne systems / L3HARRIS TECHNOLOGIES
m +1 407 538 0431 / t +1 321 309 7164
L3Harris.com<mailto:L3Harris.com>  / jim.bardgett at L3Harris.com<mailto:jim.bardgett at L3Harris.com>
407 N. John Rodes Blvd / Melbourne, FL 32934 / USA
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