Re: Request for link-layer header type (XRA)

[Guy Harris <guy () alum mit edu>]

On Dec 1, 2017, at 3:34 AM, Bruno Verstuyft <bruno.verstuyft () gmail com> wrote:

> > Type 75 is still labeled as "ODMA REQ" rather than "OFDMA REQ".  Also, it
> > says "ODMA REQ (75): as described by section 7.4.8 "REQ Messages" of the
> > DOCSIS 3.1 Physical Layer Specification. This is the "REQ message in MAC"
> > in figure 7-11 (56 bits).", but I don't see a figure numbered 7-11 in the
> > DOCSIS 3.1 Physical Layer Specification (CM-SP-PHYv3.1-I12-171026) - is
> > this from another version of that document?
>
> Apparently, the figure had number 7-11 in version I11 of the PHY spec, and
> is figure number 14 in version I12 of the spec. I updated the number to 14,
> to reflect the number in the more recent spec. I also added references to
> the DOCSIS MULPI and PHY specification version numbers, to avoid confusion
> in the future.

Figure 14 shows how it's generated, but the surrounding text doesn't say what the content is; it just says "REQ 
messages are short messages used by the CM to request transmission opportunities from the CMTS. These messages have a 
different structure than the data messages: they are always 56 bits long, they always use QPSK modulation, do not apply 
any FEC and are block interleaved."

What do the 56 bits in question contain?  Are they one of the -REQ messages described in the DOCSIS 3.1 MAC and Upper 
Layer Protocols Interface Specification, or are they something else?

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