Re: [Lsr] Doubt regarding A bit set/clear

["Les Ginsberg (ginsberg)" <[e-mail]>]

Gurusiddesh -

From: Gurusiddesh Nidasesi <[e-mail]>
Sent: Friday, April 23, 2021 5:58 AM
To: Les Ginsberg (ginsberg) <[e-mail]>
Cc: Acee Lindem (acee) <[e-mail]>; [e-mail]; [e-mail]; [e-mail]; Dona Maria John <[e-mail]>; Vikram Agrawal <[e-mail]>; Mahalakshmi Kumar <[e-mail]>
Subject: Re: [Lsr] Doubt regarding A bit set/clear

Hi Les,

Thank you very much for your response.
On top of your response, I have a few more queries. Please find them below.

1. For Min/Max Unidirectional Link Delay Sub-TLV, there is only one A-bit.



     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    |   Type        |     Length    |

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    |A| RESERVED    |                   Min Delay                   |

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    |   RESERVED    |                   Max Delay                   |

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



Does this mean A-bit is applicable only for Min-delay?

[Les:] The RFC states in Section 4.2 (emphasis added):



“A bit:  This field represents the Anomalous (A) bit.  The A bit is

      set when one or more measured values exceed a configured maximum

      threshold…”



I think the rest you can figure out for yourself.



   Les







IF not, then should we maintain 2 different maximum threshold and reuse thresholds?

And if both min-delay and max-delay values fall below reuse threshold we have clear A-bit.



Will below example follow the RFC?
min-delay reuse threshold : 50 usec
min-delay maximum threshold : 100 usec

max-delay reuse threshold : 200 usec
max-delay maximum threshold : 300 usec



1st measured value:

min-delay: 110 usec

max-delay: 190 usec

conclusion: Set A bit. (As min-delay value has exceeded max-threshold value?)

2nd measured value :

min-delay: 40 usec

max-delay: 320 usec



conclusion : Do nothing (Maintain pervious state of A bit as max-delay value has exceeded max-threshold value?)

3rd measured value :

min-delay: 40 usec

max-delay: 150 usec

conclusion : Clear A bit (As both min-delay and max-delay values are falling below resue threshold?)



Thanks & Regards,

Gurusiddesh V N


On Fri, Apr 23, 2021 at 4:51 PM Les Ginsberg (ginsberg) <[e-mail]<mailto:[e-mail]>> wrote:
Gurusiddesh –

The short answer to all your questions is “yes”.
More inline.

From: Gurusiddesh Nidasesi <[e-mail]<mailto:[e-mail]>>
Sent: Thursday, April 22, 2021 10:33 PM
To: Acee Lindem (acee) <[e-mail]<mailto:[e-mail]>>
Cc: [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>; Les Ginsberg (ginsberg) <[e-mail]<mailto:[e-mail]>>; Dona Maria John <[e-mail]<mailto:[e-mail]>>; Vikram Agrawal <[e-mail]<mailto:[e-mail]>>; Mahalakshmi Kumar <[e-mail]<mailto:[e-mail]>>
Subject: Re: [Lsr] Doubt regarding A bit set/clear

Hi All.

Gentle Reminder!

Regards,
Gurusiddesh V N

On Mon, Apr 19, 2021 at 6:54 PM Acee Lindem (acee) <[e-mail]<mailto:[e-mail]>> wrote:
Gurusiddesh,

I’ll defer to the RFC authors on your question. However, please refrain from referring to bits as being “unset”. They are set or clear.

Thanks,
Acee

From: Lsr <[e-mail]<mailto:[e-mail]>> on behalf of Gurusiddesh Nidasesi <[e-mail]<mailto:[e-mail]>>
Date: Monday, April 19, 2021 at 6:13 AM
To: "[e-mail]<mailto:[e-mail]>" <[e-mail]<mailto:[e-mail]>>
Cc: Spencer Giacalone <[e-mail]<mailto:[e-mail]>>, Stefano Previdi <[e-mail]<mailto:[e-mail]>>, "Les Ginsberg (ginsberg)" <[e-mail]<mailto:[e-mail]>>, Dona Maria John <[e-mail]<mailto:[e-mail]>>, Vikram Agrawal <[e-mail]<mailto:[e-mail]>>, Mahalakshmi Kumar <[e-mail]<mailto:[e-mail]>>
Subject: [Lsr] Doubt regarding A bit set/unset

Hi All,

I had a query regarding setting/unsetting A bit.

https://tools.ietf.org/html/rfc8570#section-4.1 states that

A bit:  This field 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 cleared, the sub-TLV represents steady-state link

      performance.



So does it mean we have to have two configurations one for reuse and another for maximum threshold?

[Les:] Yes. The goal is to prevent altering the advertisement due to small oscillations of the advertisement. If you had a single value then if the measured value bounced between (for example) +1/-1 of the threshold) the advertisement of the A-bit would change rapidly – this is undesirable.

So the max threshold triggers setting of the A-bit and the reuse threshold triggers clearing of the bit. The reuse threshold provides some confidence that the measurement has stabilized below the maximum anomalous threshold.





Will below example follow the RFC?

reuse threshold : 50 usec

maximum threshold : 100 usec

1st measured value : 110 usec

conclusion: Set A bit.



2nd measured value : 75 usec

conclusion : Do nothing (Maintain pervious state of A bit as the value is less than reuse or greater than threshold)



3rd measurement value : 30 usec

conclusion: Unset A bit.



[Les:] Yes this conforms to specified behavior.



 If we have to have two configuration for threshold to set/unset A bit, will they be different from the threshold that we use for advertisements?

[Les:] Yes .  This is clearly stated in Section 5:



“4.  For sub-TLVs that include an A bit, 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)…”
   Les



Regards,
Gurusiddesh V N

.


--
Thanks,
Gurusiddesh V N

.


--
Thanks,
Gurusiddesh V N

.