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Oscillation in the network

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Oscillation in the network

Looking at the 'broadband traffic by usage type' graph, it appears there might be oscillation in the network. The effect seems worse than some weeks ago. Have a look:



It could be just unevenness in the usage from interval to interval, but it could also be a feedback loop in the Ellacoyas. E.g. network too full so restrict, now too empty so allow, now too full etc. etc.

It could also be that the effect is all the greater since the network appears to be filling more and more, leaving just a shred of bandwidth for P2P before 11pm, and magnifying the effect of said feedback loop.

Either way, if this evening's graphs are correct, meltdown is near.
17 REPLIES
Plusnet Staff
Plusnet Staff
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Registered: 04-04-2007

Oscillation in the network

Hi,

I'm not exactly sure what you mean, looking at the graph there does appear to be a reporting error between about 4pm and 5pm which has skewed the data a little (I can see this on the internal graphs as well). Maybe I'm justing missing what you are saying, if you can clarify that would be appreciated.
Community Veteran
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Oscillation in the network

He will be referring to the spikiness of the graph. It looks like the plots are at about 5 minute intervals and go significantly up and down.

Given that P2P is supposed to use all the available capacity it is not unreasonable to expect a smooth top line at the full system capacity.
jelv (a.k.a Spoon Whittler)
   Why I have left Plusnet (warning: long post!)   
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Oscillation in the network

Yep, Elvin is right, that's what I meant.

Indeed one would expect the top line to be flat, but also interestingly even the blue HTTP line is nowhere near smooth, and from memory is much more spiky than it used to be.

Also the spikes are regular -- I would not be surprised at all if it were an oscillation caused by an undamped feedback mechanism, i.e. one as I described in the opening post rather than one which tries to prevent the effect by gradually adjusting parameters or reacting more slowly to departures from the norm.
Community Veteran
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Oscillation in the network

Actually I wouldn't expect the top to be flat as not all the gateways are dropping packets all the time. Linky

I'm assuming the graph shows the total across all Gateways, including the Tiscali LLU gateway THN-AG1. This doesn't start dropping packets until about 10 or 11 am.
jelv (a.k.a Spoon Whittler)
   Why I have left Plusnet (warning: long post!)   
Broadband: Andrews & Arnold Home::1 (FTTC 80/20)
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Oscillation in the network

OK the top not flat the whole day perhaps, but in the evening when all gateways are full you shouldn't in theory be getting the little spikes either in the top graph or the lower ones.
Plusnet Staff
Plusnet Staff
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Oscillation in the network

Ah, I see what you mean now. I think it's just a quirkiness with the graph, none of the internal graphs show the same kind of spikes. I've flagged it up though to the network guys to be on the safe side as there's definately something a little odd even if it is just the graph.
Community Veteran
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Oscillation in the network

To me, the graph shows that between noon and midnight, there is some sort of Ellanoya rule limiting p2p to a level that gives some capacity for 'other things' during that time.

SW.
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Liam
Grafter
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Registered: 04-04-2007

Oscillation in the network

I think it's more the fact that the HTTP traffic etc... is prioritised over P2P downloads - so when there is a lot of HTTP traffic on the network (between noon - midnight) then there will be less P2P (as shown on the graph.
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Oscillation in the network

obviously :roll:

Just to clarify once again, I am not talking about the large waves (of which two are visible in the window, one for each day).

I am talking about the many up and down peaks (sawteeth) visible within each hour particularly in the evening and particularly in the blue HTTP line. They smooth out at night. I'm sure they weren't there (or as prominent) a few months ago.
James
Grafter
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Registered: 04-04-2007

Oscillation in the network

I see what you're trying to see. I'll ask someone in Networks to try and get an explanation for you.
Community Veteran
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Oscillation in the network

I wonder if it's taking spot values rather than 5 minute averages (or whatever the interval is on the plots).
jelv (a.k.a Spoon Whittler)
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Oscillation in the network

That would be an explanation for what I am trying to see Smiley
Community Gaffer
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Oscillation in the network

Quote
I wonder if it's taking spot values rather than 5 minute averages (or whatever the interval is on the plots).


Yeah, kind of. the values are pulled fat intervals from the e30 switches as a counter so if 1 5 min update is missed the next will be double, which creates the spikes.

The view here is that this is an issue with the way the script is written. None of the internal e30 bundle graphs show the same issues. SNMP processes are treated as the lowest priority by the switches so even though customer traffic is not being affected, this particular SNMP request, which is very intensive is affected.

Given that I don't think the spikes are reflective of what is actually happening.

Rgds,

Bob Pullen
Plusnet Products Team
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Laugh
Grafter
Posts: 470
Registered: 07-08-2007

Oscillation in the network

Quote
Given that I don't think the spikes are reflective of what is actually happening.

Doesn't that negate the use of the graph?

Shame really! It was such a pretty graph Wink