Re: [Isis-wg] Alissa Cooper's Discuss on draft-ietf-isis-te-metric-extensions-09: (with DISCUSS and COMMENT)

[Alissa Cooper <[e-mail]>]

> On Feb 2, 2016, at 11:44 PM, Stefano Previdi (sprevidi) <[e-mail]> wrote:
>>>> 
>>>> ----------------------------------------------------------------------
>>>> DISCUSS:
>>>> ----------------------------------------------------------------------
>>>> 
>>>> (1) There seems to be some inconsistency in the way the A-bit is
>>>> described as applied to the min/max delay sub-TLV. Section 4.2 says:
>>>> 
>>>> "A-bit.  The A-bit represents the Anomalous (A) bit.  The A-bit is set
>>>> when the measured value of this parameter exceeds its configured
>>>> maximum threshold.  The A bit is cleared when the measured value
>>>> falls below its configured reuse threshold.  If the A-bit is clear,
>>>> the sub-TLV represents steady state link performance."
>>>> 
>>>> Is the A-bit meant to apply only to the min delay? Or only to the max
>>>> delay?
>>> 
>>> 
>>> As stated, is the value of max-delay that triggers the setting of the a-bit and it is used to indicate that something is going wrong with that link.
>> 
>> What do you mean “as stated”? The text does not say whether the A-bit is triggered by min delay or max delay. It says it is triggered by “this parameter,” but there are two parameters in the sub-TLV.
> 
> 
> sorry, my fault, I was looking at the wrong section.
> 
> Indeed, the A-bit is set when any of the two parameter exceeds the configured threshold.
> 
> The correct text should be:
> 
>   This field represents the Anomalous (A) bit.  The A bit is set when
>   one or more measured values exceed a configured maximum threshold.
>   The A bit is cleared when the measured value falls below its
>   configured reuse threshold.  If the A bit is clear, the sub-TLV
>   represents steady state link performance.
> 
> which is also in line with RFC7471.

Ok, this makes sense. I still think clarification is also needed in Section 5.

> 
> s.
> 
> 
>>>> Then Section 5 says:
>>>> 
>>>> "For sub-TLVs which include an A-bit (except min/max
>>>>   delay), an additional threshold SHOULD be included
>>>>   corresponding to the threshold for which the performance
>>>>   is considered anomalous (and sub-TLVs with the A-bit are
>>>>   sent)."
>>>> 
>>>> Since min/max delay is excepted from this recommendation, I don't
>>>> understand what the A-bit means in the min/max delay sub-TLV.
>>> 
>>> 
>>> if delay is higher than a configured value the a-bit is set.
>> 
>> Min delay? Or max delay? And if the min/max delay sub-TLV includes the A-bit a specified in 4.2, why is it excepted from this recommendation?