Gurusiddesh -
From: Gurusiddesh Nidasesi <[email protected]>
Sent: Friday, April 23, 2021 5:58 AM
To: Les Ginsberg (ginsberg) <[email protected]>
Cc: Acee Lindem (acee) <[email protected]>; [email protected];
[email protected]; [email protected]; Dona Maria John
<[email protected]>; Vikram Agrawal <[email protected]>;
Mahalakshmi Kumar <[email protected]>
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)
<[email protected]<mailto:[email protected]>> wrote:
Gurusiddesh –
The short answer to all your questions is “yes”.
More inline.
From: Gurusiddesh Nidasesi
<[email protected]<mailto:[email protected]>>
Sent: Thursday, April 22, 2021 10:33 PM
To: Acee Lindem (acee) <[email protected]<mailto:[email protected]>>
Cc: [email protected]<mailto:[email protected]>;
[email protected]<mailto:[email protected]>;
[email protected]<mailto:[email protected]>; Les Ginsberg (ginsberg)
<[email protected]<mailto:[email protected]>>; Dona Maria John
<[email protected]<mailto:[email protected]>>; Vikram Agrawal
<[email protected]<mailto:[email protected]>>;
Mahalakshmi Kumar
<[email protected]<mailto:[email protected]>>
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)
<[email protected]<mailto:[email protected]>> 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 <[email protected]<mailto:[email protected]>> on behalf of
Gurusiddesh Nidasesi
<[email protected]<mailto:[email protected]>>
Date: Monday, April 19, 2021 at 6:13 AM
To: "[email protected]<mailto:[email protected]>" <[email protected]<mailto:[email protected]>>
Cc: Spencer Giacalone
<[email protected]<mailto:[email protected]>>, Stefano
Previdi <[email protected]<mailto:[email protected]>>, "Les Ginsberg
(ginsberg)" <[email protected]<mailto:[email protected]>>, Dona Maria John
<[email protected]<mailto:[email protected]>>, Vikram Agrawal
<[email protected]<mailto:[email protected]>>,
Mahalakshmi Kumar
<[email protected]<mailto:[email protected]>>
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
.
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