Re: How do you negotiate a numerical range?

[Paul Koning <ni1d@arrl.net>]

Excerpt of message (sent 17 July 2002) by Bill Studenmund:
> I think I know the answer, but wanted to double check as AFAICT all the
> numbers we have in the spec are either MIN or MAX; I suspect not much code
> is using numerical ranges at the moment. Also, the spec doesn't say
> anything about negotiating ranges AFAICT. :-)
> 
> Question 1:
> 
> Since all of the numbers we have are MIN or MAX, my understanding is that
> you just take the min or max of the range, and use that for negotiation.
> 
> The initially-non-intuitive thing is that you can readily get a negotiated
> value outside of the offered range. :-)
> 
> Consider an offer of "MaxConnections=3~10" to a device that wants
> MaxConnections=2. Since MaxConnections is a MIN number, the correct
> response (I believe) is "MaxConnections=2". I suspect however this might
> seem counter-intuitive for new implementers.

No, you are misreading the spec.

Only the marker interval parameters (OFMarkInt, IFMarkInt) permit
ranges.  It is not permitted for any other parameters (see section
4.2).

For range proposals, the responder must choose a value from within the
range, or Reject.  A response value outside the range is a protocol
error, the same way that picking a value not in the list for a list
type proposal is a protocol error.

MIN and MAX apply to parameters for which a single value is offered,
and the responder is allowed to negotiate down, or up, respectively.


> Question 2:
> 
> Say you have a number that is not a MIN or MAX number (right now this'd be
> a vendor-specific one), and you are offered a range (say "Foo=3~12"), and
> had you made the offer you would have offered a different range (say
> "Foo=10~16"). Do we want to say anything now about how to handle this
> negotiation, or do we want to wait until we actually have a non-MIN/MAX
> number in the spec?

The rule for ranges is already specified (section 4.2.2): one side
proposes a range, the other side chooses from that range.  If someone
adds an X-foo parameter which is a range, that rule would apply.

	  paul