Re: [Gen-art] Gen-ART Telechat review of draft-ietf-manet-olsrv2-metrics-rationale-03.txt

[Suresh Krishnan <[e-mail]>]

Hi Christopher,
  Thanks for your quick response. Trimming the stuff we agree on

On 04/24/2013 05:18 AM, Dearlove, Christopher (UK) wrote:
> Thank you for this, some comments below, marked CD> (Generally, where I haven't commented, I think the point is good.)
> 
>> -> Describe a short algorithm for converting a metric value into a
>> compressed metric. i.e. Given a metric value x, how to obtain a and b
>> from it. e.g.
>>
>> b=log2(x+256)-9
> CD> Such an algorithm is already in the OLSRv2 draft, it does not
> seem necessary to repeat it. It could of course be referred to.

Sounds good. Please add the reference to the OLSRv2 spec Section 6.2 for
the conversion.

>> * To achieve interoperability and to avoid loops, the values of e
>> and m need to be the same across the network. The following sentence
>> seems to allow for other values of e and m ("An appropriate
>> pair..."). Suggest
>>
>> OLD:
>> The required 24 bit limit can be achieved if 2^e+m = 24. An
>> appropriate pair of values to achieve this is e = 4, m = 8.
>>
>> NEW:
>> The required 24 bit limit can be achieved if 2^e+m = 24. Since
>> e+m=12, solving for e and m will lead to e = 4, m = 8.
> CD> The NEW text is incorrect, because it assumes e+m = 12 was an
> input to the process. Rather those possible pairs that satisfied
> 2^e+m = 24 were considered, and the preferred (e.m) pair selected,
> which conveniently gave e+m=12. (I remember when first doing this,
> and the satisfaction that it gave 12, which left the 4 bits we
> wanted, but up to that point were doing differently, was great -
> sometimes things do work out well.) So while the point that this is
> fixed is good (but clearly in OLSv2 a single choice is used)
> different alternative wording would be needed.

Not sure what you mean here. The OLSRv2 link metric is 12 bits long
according to the OLSRv2 draft. So e+m need to add up to 12, right?. In
any case, go for any wording that works for you as long as it ensures
that all the routers in the system will use the same value for e and m
and the metric will fit in the OLSRv2 LINK_METRIC TLV.

Thanks
Suresh