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Author Topic: Constipated Networks  (Read 2567 times)

hake

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Constipated Networks
« on: September 29, 2009, 08:33:46 AM »

Mornin' all.  After a few months of iffy health, I am back in the fray.  Thanks to all who gave their time and thoughts to help me resolve the line problems that I had put up with for over three years since MaxADSL arrived.

Eventually, replacement of a faulty filtered faceplate seemed to effect the crucial improvement.  It was a pyrrhic victory.  Although disconnects are now unknown and I see a synch speed of 5240kbps, the networks my traffic passes through are seemingly constipated.  I am guessing that router congestion is a very real issue at certain times.  There may also be an issue with contention on the other side of the telephone exchange.  Web sites no doubt suffer from constipation with servers struggling against lengthening queues as demand outstrips supply.

At times, the real downstream speed reaches 4000kbps but it can be as low as 2000kbps at certain times on certain days (using www.speedtester.bt.com).  I enquired at PlusNet, my ISP about this and received advice that I should connect through the test socket ???.  Clearly, whoever answered my enquiry had either not understood it or had not read it properly.

I have done what I can to optimise my TCP/IP settings.  MTU is 1430, RWIN is 111200, window scaling, time stamping, selective acks, path MTU discovery and black hole detection are all enabled, max duplicate acks is 2, TTL is 128, my router's MTU is also 1430 and it is permitted to respond to pings.

There must be something I am failing to take account of but I cannot help thinking that the UK internet infrastructure is analogous to our congested motorway network and congested motorway junctions are analogous to congested routers.
« Last Edit: September 29, 2009, 08:36:01 AM by hake »
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roseway

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Re: Constipated Networks
« Reply #1 on: September 29, 2009, 10:05:58 AM »

No simple answers, I'm afraid. Some exchanges are congested, some aren't. Some users are subject to ISP traffic management measures, some aren't. Some servers have capacity limitations, some don't. But the BT speedtester shouldn't be subject to the last two issues, so I guess it's either exchange congestion or your personal configuration (and the latter sounds quite unlikely from what you say). You can check the status of your local exchange with the PlusNet exchange status checker.
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hake

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Re: Constipated Networks
« Reply #2 on: September 29, 2009, 10:37:42 AM »

Thanks Mr Roseway.  Do heavy users, such as iPlayer users, cause exchange congestion and so penalise those who make 'fair' use?

My internet traffic is bursty because I browse and email and only do the occasional software download.

I have a notion that I am subsidising the BBC and others because I pay a price for others to indulge in 'unfair' use to my disadvantage.  I understand the phenomena of router congestion and consider that a packet switched network is not the place for huge amounts of streaming video and video downloads.  If the BBC and others wish to distribute their products over the internet, the cost of providing an adequate infrastructure must be met by the users of that particular traffic.  That does not include me.  I will continue to watch scheduled TV programmes and buy music CDs: Mahler sounds far better on CD than MP3 and better still on vinyl.

There will always be people who spoil things for everyone else.
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roseway

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Re: Constipated Networks
« Reply #3 on: September 29, 2009, 11:17:06 AM »

I've got some sympathy with your view there because we're all sharing a limited resource and some make much more use of it than others. But it's probably not right to describe heavy use as unfair. People buy internet access according to the terms and conditions offered, and if they operate within those conditions then they can't really be criticised for making use of what they've paid for.

I personally agree with you about the BBC and other broadcasters who are responsible for a great deal of bandwidth usage, when there are already perfectly good wireless distribution systems for TV and radio. But that particular genie is out of the bottle and it's not going to go back in, so we have to live with it. There's an argument for PAYG charging so that heavy users pay more than light users, but as I type that I can already hear the outrage from people who would pay a lot more under such a system. :)
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  Eric

hake

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Re: Constipated Networks
« Reply #4 on: September 29, 2009, 01:07:29 PM »

All the outrage in the world won't make a packet switched network suitable as a broadcast medium.  The whole principle of the thing means that failure to ration use by price will, sooner or later, make it unusable.  I refuse to fund the profligacy of others.  You can add lanes to motorways but that doesn't lessen junction (router) congestion.  In fact, more lanes produce worse junction congestion.

The internet will thrash itself to a standstill as overwhelmed routers drop packets by the squillion and speed rapidly backs off to zero.  I imagine that there is some twist with the law of diminishing returns when applied to network routers, no matter how numerous and powerful they are.

We are too used to getting what we want.  The laws of nature are supreme.  Having a tantrum will make no difference.  Perhaps power cuts a few years hence will mitigate router congestion.

The impossible can happen as the Romans found when the barbarians arrived.  Let us not kid ourselves that the internet will always be serviceable.  eBay users already know better.  It's one of those mechanisms that is liable to fall off a cliff when it glues up.
« Last Edit: September 29, 2009, 01:10:34 PM by hake »
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kitz

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Re: Constipated Networks
« Reply #5 on: September 30, 2009, 03:22:44 PM »

Hake...  just out of interest which account are you on with plusnet.

This is a longshot...  and I may be speaking out of turn... but I strongly suspect that the old BroadbandPlus account doesnt perhaps get as much priority as some of the more recent accounts.
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hake

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Re: Constipated Networks
« Reply #6 on: September 30, 2009, 07:33:55 PM »

Thank you Kitz.  I'm on PlusNet Unlimited Broadband.  I was on a Premier account until a few months ago.  The picture has been made less clear because I resolved connection problems during this interval.

I have just tried the speed test available through the PlusNet portal ( http://www.mybroadbandspeed.co.uk ) at 1930hours and was measured as downstream 4050kbps and upstream 367kbps.  I can't complain too much about that.
« Last Edit: September 30, 2009, 07:49:09 PM by hake »
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kitz

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Re: Constipated Networks
« Reply #7 on: September 30, 2009, 11:05:14 PM »

>> I'm on PlusNet Unlimited Broadband.

OK good stuff...  was just checking and ruling out all possibilities.   Premier should have been ok anyhow.

Glad that it seems to have cleared tonight for you.  Was the status at your exchange ok?
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hake

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Re: Constipated Networks
« Reply #8 on: October 01, 2009, 07:35:43 PM »

Yes, it was, thanks.   :o
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Chrysalis

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Re: Constipated Networks
« Reply #9 on: October 10, 2009, 07:15:11 AM »

I know I am replying to an old post, but of the list of settings you have turned on I would suggest turning off black hole detection.

normal mtu discovery will start with your configured mtu (in your case 1430) and if it detects a lower mtu router then your mtu will drop otherwise it will use 1430.
blackhole discovery method defaults to a 576 mtu and works its way up until it sees retransmits, it has a performance hit because of the ramp up time and sometimes can result in triangular speed graphs as it often resets to 576 during data transfer.
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hake

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Re: Constipated Networks
« Reply #10 on: October 10, 2009, 11:21:45 AM »

Thanks Chrysalis.  I wasn't aware of that.
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