Hi Charlie,
Thanks for the replies on this - I'm gradually catching up.
Further comments in line...
On Thu, Apr 16, 2015 at 10:32 PM, Charlie Perkins <
charles.perkins@xxxxxxxxxxxxx> wrote:
Hello Vicky,if they worked out the Cost and LoopFree functions, might be able to.
Follow-up below...
On 4/16/2015 7:00 AM, Victoria Mercieca wrote:
This email is about metrics (Section 7 in Version 9a or Section 5 in
Version 9b):
- We refer to RFC6551. This defines more than just HopCount = 3. e.g.
node energy, link throughput, link latency, link reliability and ETX
reliability. Our IANA section doesn't list these under MetricTypes,
actually it says those numbers are unallocated. Should we change this?
The problem is that some of the metrics in RFC 6551 are not monotonically
increasing,
like the reliability metrics. In my opinion this is a problem that needs
to be fixed, but
we can't do that right now.
We dont support them, fair enough, but someone writing an implementation,
- "monotonically increasing" means increasing or remaining constantincreasing" then?
(i.e. anything but decreasing), so is it more correct to say "strictly
increasing"? For hopcount at least, Cost(L) is always 1 and route cost will
always increase with number of links. We can support any strictly
increasing metric using Cost(R) = sum of Cost(L), and our current LoopFree
function, I think. Charlie previously said link cost could be less than one
for some metrics. Since alternate metrics are out of scope anyway, I don't
know if that's relevant. They would need different Cost and LoopFree
functions. Is "strictly increasing" the same as "additive"? From some
Google searching, "additive" seems to refer to metrics themselves, whereas
"monotonically" or "strictly increasing" would refer to the route cost
function.
I think that strictly increasing is better actually.
Should I replace uses of "monotonically increasing" with "strictly
The definitions of our abstract functions should not depend on whether the
minimum positive metric is 1.
Latency is a good example of such an strictly increasing (and additive)
metric. I reckon that as soon as we
get into Last Call, we (or I) should be looking at enlarging the number of
metrics available.
Strictly increasing is not the same as additive.
So I'm still a bit confused. What's the difference?
- Should we have a configuration option for MetricTypes in use? Or
should we support all metric types we see in received messages? Or is this
what is meant by "check that the metric type is known"?
I am O.K. to describe this as a configuration option. However, it is new
text about
something that no one was complaining about. But if the text is written,
I am sure
no one would complain about that either :-)
What about this:
Lotte previously said:
- We havent decided on whether to make default metric type 0 for
simplification.
Well, RFC 6551 says that hopcount is type 3, so it would be bad to also
have it be type 0.
Charlie P.