Re: RTS/CTS + CTS-to-self

On Sat, Aug 22, 2009 at 12:47:19AM +0200, Gábor Stefanik wrote:
> On Sat, Aug 22, 2009 at 12:35 AM, David Young<[email protected]> wrote:
> > On Fri, Aug 21, 2009 at 11:55:27PM +0200, Gábor Stefanik wrote:
> >> 2009/8/21 Johannes Berg <[email protected]>:
> >> > On Fri, 2009-08-21 at 17:04 +0200, Gábor Stefanik wrote:
> >> >
> >> >> I've reworked RTS/CTS since then, just haven't got to sending a new
> >> >> proposal yet. The current plan is as follows:
> >> >>
> >> >> TX_FLAGS & 0x0002: Use CTS
> >> >> TX_FLAGS & 0x0004: Use RTS
> >> >> TX_FLAGS & 0x0020: Disable RTS/CTS usage
> >> >
> >> > Seems a bit strange, wouldn't setting neither RTS nor CTS have the
> >> > effect? Seems like 0x20 should rather be "use automatic and ignore the
> >> > other bits". Anyway, not appropriate here, you should just bring a new
> >> > proposal.
> >>
> >> The point is that if all bits are 0, auto-setup is used. The problem
> >> with my original proposal (using two bits) was that an all-zero value
> >> had different effect than not including the TX flags field (and simply
> >> swapping "none" and "auto" would result in an illogicality where what
> >> would logically be "use both" would become "use neither" - just the
> >> opposite of its logical meaning). Making 0x20 mean "Auto-select
> >> RTS/CTS", interpreting all-zeros as "Use neither", would have the same
> >> problem as my proposal - all-zeros is different from a missing field.
> >> (An empty, zeroed field 15 should have no effect on the process,
> >> behaving as if field 15 was not present in the header.)
> >
> > Gábor,
> >
> > Please explain what is wrong with a two-bit (four-state) field like
> > this?
> >
> > 00: Let the hardware, firmware, or device driver decide.  (I.e., same as
> >    omitting Tx flags altogether.)
> > 01: Send RTS/CTS.
> > 10: Send CTS to self.
> > 11: Forbid CTS-to-self and RTS/CTS.
> 
> The 11 case is illogical. The logical meaning of 11 would be "use
> both", but it actually means "use neither" - just the opposite.

You may have misunderstood.  When I say to treat it as a two-bit field,
I mean to treat it as an integer that is two bits wide.  That is, I am
not talking about flags any longer.  I may as well have written the
values in decimal:

0: Let the hardware, firmware, or device driver decide.  (I.e., same as
   omitting Tx flags altogether.)
1: Send RTS/CTS.
2: Send CTS to self.
3: Forbid CTS-to-self and RTS/CTS.

I don't care too much which value maps to what function, except that 0
must mean "don't care."  I think we agree about that much?

According to my notes, somebody may already use Tx flags 0x2 and 0x4 to
indicate CTS protection and RTS/CTS handshake, respectively, so this
assignment may be most practical:

Tx Protection Field, Bits [3:2]
Values:
        0: Let the hardware, firmware, or device driver decide.  (I.e., same as
           omitting Tx flags altogether.)
        1: Send CTS to self.
        2: Send RTS/CTS.
        3: Forbid CTS-to-self and RTS/CTS.

Ok?

Dave

-- 
David Young             OJC Technologies
[email protected]      Urbana, IL * (217) 278-3933