Hi all,
Just refreshing this email:
- We refer to RFC6551. This defines more than just HopCount = 3. e.g.implementation, if they worked out the Cost and LoopFree functions, might
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
be able to.
I would suggest that we dont mark those numbers as unallocated in our
AODVv2 draft. Perhaps at a minimum do it like this:
MetricType Type
------------------ ----
Unassigned 0
Currently Unsupported 1 - 2
Hop Count 3
Currently Unsupported 4 - 8
Unallocated 9 - 254
Reserved 255
What do you think?
Any comments?
Interestingly there are fields mentioned in RFC 6551 which signal that
the metric is additive, maximum, minimum or multiplicative. For future
discussion perhaps.
- "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
Covered in last Hangout, see next comment.
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?
Covered in last Hangout.
- 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:
An AODVv2 implementation MAY be configured to use a limited set of the
supported metric types. In the processing described in [Section on
messages], a known MetricType can be
interpreted as a configured MetricType. If a message is received using an
unknown or non-configured
MetricType it will be ignored. If the message is not regenerated, other
routers which do support the
MetricType will not be able to route through a router which does not
support the MetricType.
Any comments?
- We havent decided on whether to make default metric type 0 forLotte previously said:
simplification.
Well, RFC 6551 says that hopcount is type 3, so it would be bad to also
have it be type 0.
- Henning confirmed to me what he wrote on the list[1]: When using
extension types, If we set DEFAULT_METRIC_TYPE to 0, this will save us 1
byte as opposed to leaving DEFAULT_METRIC_TYPE at 3, because: the
*variable* tlv-type-ext is *always* set, and it is set to 0 by default.
If the <tlv-type-ext> *flag* is set, too, tlv-type-ext will have the
value that <tlv-type-ext> has. So the exttype 0 is always set, and we
just need to make use of it.
RFC 5444 says:
tlv-type-ext is a variable, defined to equal <tlv-type-ext>, if present, or
0 otherwise.
I might not completely understand, but this is what I was thinking:
If our configuration says DEFAULT_METRIC_TYPE is 3 (HopCount) and we
dont include a MetricType when we are talking about DEFAULT_METRIC_TYPE,
isn't the lack of a value in RFC5444 kind of the same as including a value
of zero? What does the receiving node see - either metricType 0, or no
MetricType included. Either way, wont it interpret this as
DEFAULT_METRIC_TYPE, i.e., 3?
I think this is a good solution.
Me too.
