[Sls-slp] FW: inconsistent bit numbering for CLCWs in AOS and TM Space Data Protocol specs

[Kazz, Greg J (313B)]

Dear SLP,


A new RID for disposition at the SLP meeting in Cleveland. Please see below.

Thanks John!


Greg Kazz
Chairman CCSDS SLS-SLP WG
From: John Pietras <john.pietras at gst.com<mailto:john.pietras at gst.com>>
Date: Monday, July 30, 2012 2:46 PM
To: "Kazz, Greg J (313B)" <greg.j.kazz at jpl.nasa.gov<mailto:greg.j.kazz at jpl.nasa.gov>>
Subject: inconsistent bit numbering for CLCWs in AOS and TM Space Data Protocol specs

Greg,
There’s inconsistent usage of “first” bit in the AOS and TM Space Data Protocol specs (732.0-B-2 and 132.0-B-1, respectively).

The boilerplate section 1.6.3, Conventions, states “The first bit in the field to be transmitted (i.e., the most left justified when drawing a figure) is defined to be ‘Bit 0’ ”, and that’s also illustrated in figure 1-1.

However, in section 4.1.5 (OPERATIONAL CONTROL FIELD) the following statements appear:

4.1.5.4 The leading bit of the field, i.e., bit 0, shall contain a Type Flag with the following meanings: …
4.1.5.5 The first bit of a Type-2-Report (i.e., bit 1 of the Operational Control Field) shall indicate the use of this report as follows: …



The last sentence of NOTE 2 under 4.1.5.5 reads “This issue of the Recommendation does not define the use of Type-2-Reports; however, it reserves the possibility to do so in future issues by restricting the utilization of the first bit.”

That is, 4.1.5.4 uses the otherwise-undefined term “leading bit” to refer to bit 0, and 4.1.5.5 uses “first bit” to refer to bit 1.

To be consistent with the Conventions ion 1.6.3:

-           4.1.5.4 should read  “The first bit of the field, i.e., bit 0, shall contain a Type Flag with the following meanings: …”

-           4.1.5.5 should read “The second bit of a Type-2-Report (i.e., bit 1 of the Operational Control Field) shall indicate the use of this report as follows: …”, and

-          The last sentence of NOTE 2 under 4.1.5.5 should read “This issue of the Recommendation does not define the use of Type-2-Reports; however, it reserves the possibility to do so in future issues by restricting the utilization of the second bit.”

Something to file away in your list of errata to eventually be fixed.

Regards,
John


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