Subject: [PCN] T-maxsuppress and T-fail

From: Tom Taylor <[email-masked]>
Date: Wed, 9 Mar 2011 22:05:05 -0500

T-maxsuppress and T-fail in the edge behaviour drafts are causing me, at 
least, some difficulty because of the tie-in with the as yet undefined 
transport protocol. Given that they are application-level timers, could 
we simply recommend values based on the application requirements and 
leave it at that?

My gut feeling is that a value of 10 seconds for T-maxsuppress is 
probably a reasonable balance between reducing the volume of unnecessary 
signalling and feeling comfortable that things are working properly. It 
is also long enough to ride out temporary losses of communication that 
would be alarmed on a different level if at all.

T-fail is a more complex matter. I'd feel uncomfortable setting it 
higher than 5 seconds if report suppression is not deployed. If report 
suppression is deployed, I would consider having two regimes: a limit of 
5 seconds if the CLE in the last report received was greater than the 
reporting threshold, and a limit of 3 * T-maxsuppress if the CLE in last 
report received was not greater than the reporting threshold.

If this sounds vaguely familiar except for that last twist it's because 
that's how we used to have it. But I think that last bit of logic is a 
reasonable addition. It says that receiving timely reports is more 
critical when our latest information suggests that pre-congestion may be 
present.

Tom Taylor

---

From: "Georgios Karagiannis" <[email-masked]>
Date: Thu, 10 Mar 2011 12:24:51 +0100

Hi Tom

I think that I agree with your proposal on recommending default values for
T-maxsuppress and T-fail in combination 
with (1) the motivation of choosing these value and (2) a
guideline/method/requirements on how these values could be defined in the
future.

Best regards,
Georgios

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]] On 
> Behalf Of Tom Taylor
> Sent: donderdag 10 maart 2011 4:05
> To: pcn
> Subject: [PCN] T-maxsuppress and T-fail
> 
> T-maxsuppress and T-fail in the edge behaviour drafts are 
> causing me, at least, some difficulty because of the tie-in 
> with the as yet undefined transport protocol. Given that they 
> are application-level timers, could we simply recommend 
> values based on the application requirements and leave it at that?
> 
> My gut feeling is that a value of 10 seconds for 
> T-maxsuppress is probably a reasonable balance between 
> reducing the volume of unnecessary signalling and feeling 
> comfortable that things are working properly. It is also long 
> enough to ride out temporary losses of communication that 
> T-fail is a more complex matter. I'd feel uncomfortable 
> setting it higher than 5 seconds if report suppression is not 
> deployed. If report suppression is deployed, I would consider 
> having two regimes: a limit of
> 5 seconds if the CLE in the last report received was greater 
> than the reporting threshold, and a limit of 3 * 
> T-maxsuppress if the CLE in last report received was not 
> greater than the reporting threshold.
> 
> If this sounds vaguely familiar except for that last twist 
> it's because that's how we used to have it. But I think that 
> last bit of logic is a reasonable addition. It says that 
> receiving timely reports is more critical when our latest 
> information suggests that pre-congestion may be present.
> 
> Tom Taylor
> _______________________________________________
> PCN mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/pcn
>

---

From: Tom Taylor <[email-masked]>
Date: Thu, 10 Mar 2011 07:39:43 -0500

Just to summarize this proposal:

Timeout behaviour by the Decision Point

The Decision Point resets the timer t-fail each time it receives a 
report for a given IEA. The timer limit depends on the following logic:

a. If report suppression is not enabled, the timer limit is always T-fail.

b. If report suppression is enabled and the latest report contained a 
CLE value greater than CLE-reporting-threshold, the timer limit is T-fail.

c. If report suppression is enabled and the latest report contained a 
CLE value not greater than CLE-reporting-threshold, the timer limit is 3 
* T-maxsuppress.

If timer t-fail expires, the Decision Point SHOULD raise an alarm to 
management, etc.

Suggested default values:

T-fail: 5 seconds
T-maxsuppress: 10 seconds