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Author Topic: ADSL2+ QoS and Day Time PPP Dropouts Without Retrain.  (Read 6326 times)

j0hn

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Re: ADSL2+ QoS and Day Time PPP Dropouts Without Retrain.
« Reply #15 on: May 04, 2019, 11:09:50 PM »

The xDSL link breaking (a retrain) will result in the PPP link breaking.
The PPP link disconnecting would have no impact on the xDSL link.

In respect of the rules I am posting a link to community BT and I am also lazy.

https://community.bt.com/t5/ADSL-Copper-broadband/PPP-Dropouts-during-day-remote-station-is-not-answering-to-LCP/td-p/1940705/page/3

Page 3 is my question. Save you a read.

I'm also lazy.

I haven't read the BT thread but all I can see from the logs is that the DSL link is breaking.

Too much unrelated stuff in the logs which also show in reverse, it's difficult to tell what I'm supposed to be looking for.
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DiggerOfHoles

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Re: ADSL2+ QoS and Day Time PPP Dropouts Without Retrain.
« Reply #16 on: May 05, 2019, 07:48:35 AM »

Thanks for reply.


The PPP is more breaking thus disconnecting.


The loss of ?LCP echo packets is causing my end to bring down PPP session and retry while xDsl is still up.

The symptom is everything grinds to a halt. Ususl at congersted times but should get going again.

Mine will slow down, PPP echo's x 6? not answered, stop PPP session restart PPP with new external IP.

There are two patterns. I've had a serious line fault for 12months masking this symptom.

With fault 90% of time PPP lost then xDSL link will go down 60 to 90 seconds later. 10% PPP reestablished and carry on.

Now fault fixed, line still training, when it does it 2-3 times a week I'm generally when doing something important.

It will now 90% drop PPP reestablish PPP and carry on. 10% a retrain will occur 60-90s later.

I have two theories 1. R.E.I.N 2. 'black holeing' LCP echo requests getting dropped after xDSL link.


1. I have de rein'd my place late 2018. Everything from toaster fridge boiler ...... x rated capacitors, filters mu metal shielding the lot.

before I retired I worked in pro audio. We call it noise no rein. Spent many years finding clics, pops and hums on FST twisted pair.

I am going to dump BT hub soon and start graphing my SNR in real time. Will check for impulse noise then.


2. I personally think this is my problem. Backhaul load balancing packet filtering and Best Effort.

All of my control data and ordinary data are being tagged BE or not, if no tag they get default BE tag.

I expect also BT are intentionally dropping some control traffic, saving bandwidth for them, all the time anyway.

At times of congestion because all my data is BE it will drop enough PPP control packets to make PPP drop and reestablish.

It would appear if this takes more than 60 seconds ish BT firmware will bring down xDSL as a turn it off then turn on style fix.


I suspect my line is misconfigured , or I need a business 'product' for this configuration,or a radius server malfunctioning.

As with everything BT they talk s...e. retrain = loss of sync. training = stabilisation rate cap = we don't do caps(yet they do) etc ...

BT take the p..s most of the time. Use the 'wrong' language and you find another black hole.

Mention PPP to level 1 and they start banging on about interleaving. God forbid you mention the blue light stays on.

Blue light = get the cables out and have another hour of my time wasted. Nothing wrong with my side.


For 12 months my ADSL has had DLM off and SNR target locked to 6dB. Software fudge to 'fix' hardware(line) fault.

After fixing line fault, 40+ engineers have worked on it in 12 months, upgrade to ADSL2+ DLM on SNR floating.

But if BT, Level1 or Openreach 'reset' my line it goes DLM off SNR locked.


BT said it cold not happen but it did. They now 'say' it won't happen in the future.

I suspect 'the it won't happen again' is an assumption based default behavior and not my actual line settings.


So as BT don't care I am left to diagnose the fault my self.

Find the correct BT speak to describe it.

Then give the f...g bunch of c..s the biggest b.....g they have ever had in there lives.

In 1990's I got bt regional manager out of bed at 4am on a Sunday morning.

When he arrived in my office at 5:30am he got a right b......g for cutting off 25+ lines for no reason at all.

But I was a business customer not a retail where all BT customers are called Terry F...wit.

6 months and I'm off. Sorry for the ranting.
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j0hn

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Re: ADSL2+ QoS and Day Time PPP Dropouts Without Retrain.
« Reply #17 on: May 05, 2019, 02:28:52 PM »

Quote
With fault 90% of time PPP lost then xDSL link will go down 60 to 90 seconds later. 10% PPP reestablished and carry on.

This suggests the fault lies in the copper xDSL link, not anything backhaul related.

As mentioned above

The xDSL link breaking (a retrain) will result in the PPP link breaking.
The PPP link disconnecting would have no impact on the xDSL link.

The fact the logs mention the PPP link is disconnecting 1st is irrelevant.

Sounds like you are over thinking this also.
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DiggerOfHoles

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Re: ADSL2+ QoS and Day Time PPP Dropouts Without Retrain.
« Reply #18 on: May 05, 2019, 03:46:59 PM »

Thank for input. Line fault is now fixed.

Now fault fixed, line still training, when it does it 2-3 times a week I'm generally when doing something important  Edit: at peak times.

It will now 90% drop PPP reestablish PPP and carry on. 10% a retrain will occur 60-90s later.

I have two theories 1. R.E.I.N 2. 'black holeing' LCP echo requests getting dropped after xDSL link.

Over Thinking is my middle name!

Ta.
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DiggerOfHoles

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Re: ADSL2+ QoS and Day Time PPP Dropouts Without Retrain.
« Reply #19 on: May 06, 2019, 07:38:27 AM »

I think to answer my question I need one piece of information.


Does any one know how BT(ISP) WBC(Openreach) ADSL1(Max) and ADSL2plus establish a PPP session?


PTA mode or L2TP mode?


Is this arrangement ISP specific? ie Small ISP PTA BIG L2TP


This will hopefully ctrl alt delete my over thinking and stop me waffling.


And stop me getting a full reboot from the wife for not cutting the grass!


Unless the sound of my typing wakes the dragon. Thanks again.
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Weaver

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Re: ADSL2+ QoS and Day Time PPP Dropouts Without Retrain.
« Reply #20 on: May 06, 2019, 10:59:56 AM »

Digger, ADSLx has absolutely nothing at all to do with PPP or L2TP. PPP was in use 23 years ago in the dialup days before ADSL existed. Iirc some ISPs do not use PPP with internet access at all, rather using other protocol stacks. See http://wand.cs.waikato.ac.nz/~513/2006/readings/adsl-2.pdf

Kitz has talked about the business of setting up PPP links with internet access. If memory serves, the user initially connects to the BT ‘BRAS’ server - see Kitz’ articles on how internet access works which have a diagram of nodes and links in the access provision network. The BRAS server handles user login with something like bob@my.isp and can (optionally?) give out IP addresses too as instructed by the ISP.

It is a bit strange in protocol terms because first the user’s router is talking to the BRAS, and then the BRAS goes transparent and after that point your are talking through the BRAS to a server at the ISP. During this later phase the user is exchanging data with the ISP using PPP packets. (We are supposed to call these packets ‘frames’. I don’t care.)

L2TP is used for the link between BRAS and the LNS server at the ISP. It carries user data. L2TP can be used between your own router or your own machine and an LNS at your ISP or at your company HQ. It’s a tunnel protocol that is an insecure VPN because as it comes out of the box there’s no encryption included. Aside from the usual role in internet access with wholesale carriers, a very different example: for £10 + VAT per month you can connect your router or other machines of yours to the ISP AA.net.uk and use their services to access the internet even though you are accessing them using some other ISP or service, could be anything, some other DSL, or 4G or a wireless network in a café. L2TP takes PPP packets for example and carries them down a tunnel to l2tp.AA.net.uk. See https://www.aa.net.uk/broadband/l2tp-service

Is L2TP ISP-specific ? - in the usual wholesale L2TP is between wholesale carrier and ISP - kitz or one of our experts could answer this question. My ISP uses L2TP and I would have thought a great many do, but everyone? Some ISPs use their own network to get data from the exchange to their own core kit rather than using a wholesale carrier - LLU operators are often like this, so they could do whatever they like, but that doesn’t tell us much. Over to others who know what’s what.

Sorry I couldn’t be of much help, don’t know enough isps.
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DiggerOfHoles

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Re: ADSL2+ QoS and Day Time PPP Dropouts Without Retrain.
« Reply #21 on: May 06, 2019, 12:52:32 PM »

Weaver, Thanks for reply.

You must be a mind reader I was going ask you about AA. I'm considering Aquiss.

https://www.btplc.com/SINet/SINs/pdf/472v2p9.pdf

This is the current document on wholesale? website WBC 'product'

This is how my current adsl2plus service is curently described as being supplied.

With reference to this 'language' and it's 'proper' name.


Router remains 'synced' for three days.

Day two 10:30am no internet. 10:32am internet back with different external dynamic IP?

What mechanism or concept would you have to 'break' to observe this behavior?

Infrastructure upgrades software etc. is usually done at 4am.

I can then reverse engineer your answer into language BT/Openreach speak.

I suspect in my language that my session control traffic is getting dropped at congested times.

I expect this to happen with my data but not to dump my current session at the same time.



My router makes a 'link' to the exchange, my xDSL.

My router then makes a different link using the xDSL link to my ISP ie the internet.

What else could cause the link to fail apart from the xDSL link failing?


PPP LCP Send Termination Request (Peer not responding)

This appears in router log when this happens.

Sorry to bang on. Any Ideas?

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aesmith

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Re: ADSL2+ QoS and Day Time PPP Dropouts Without Retrain.
« Reply #22 on: May 06, 2019, 03:09:29 PM »

Probably not that helpful but I can confirm that I've also been having a fault where the PPP drops while DSL remains in sync, sometimes for hours.  PPP only comes back by initiating a DSL retrain.   I know DSL is staying in sync because the router shows this, complete with variations in SNR and incrementing counters to show it's not just frozen at the last known set of stats.  Also on A&A's portal you can get a sync status report from BT, and that also shows the line in sync.   Getting Openreach to believe is a different matter - even after getting all the facts from AA and from me they keep referring to what might be causing it to "lose sync".
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DiggerOfHoles

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Re: ADSL2+ QoS and Day Time PPP Dropouts Without Retrain.
« Reply #23 on: May 06, 2019, 03:26:32 PM »

A matter of correct language and identify the owner of kit responsible.

I suspect an over zealous/worked backhaul router. Where of who impossible to find out.

I am also expecting Openreach again tomorrow. Tea, cake and football chat then. FA will get done.

I'll keep digging.
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DiggerOfHoles

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Re: ADSL2+ QoS and Day Time PPP Dropouts Without Retrain.
« Reply #24 on: May 08, 2019, 07:59:17 PM »

I realise that I forgot to say that the link drops could be due to an echo request-response pair in the d/s-request-then-u/s-response direction which is initiated by the Firebricks at the A&A end which always do such monitoring. So if I were corrupting anything sent upstream, it could be an echo response that is being corrupted. Those remote Firebrick’s LCP link monitoring timers are iirc not user-controllable to such a fine degree; I don’t recall seeing any facility for users to enter values for timeouts. There is however a 1-bit control, "fast" ie. short or normal timeout. The clueless.aa.net.uk help file says
Quote

    LCP echoes usually stop responding if the line has gone down. Our LCP monitoring, which produces the graphs, will drop the line if there are no replies after 60 seconds. When bonding or used in a fall-back setup, having a faster timeout is useful in order to fall-back quicker.



Above from. https://forum.kitz.co.uk/index.php/topic,23382.msg396417.html#msg396417


LCP echoes usually stop responding if the line has gone down.

Is not the same as

Our LCP monitoring, which produces the graphs, will drop the line if there are no replies after 60 seconds.


LCP echoes usually stop responding if the line has gone down.
The word 'usually' is strange if the line is down, I presume they mean loss of sync by line down. It is 'normal' no sync nothing gets through. Everything breaks.

Our LCP monitoring, which produces the graphs, will drop the line if there are no replies after 60 seconds.
Ie line in sync but no LCP arriving at ISP. ISP thinks PPP link broken and can only resyncs line to fix lost session.

It appears to work in the opposite direction. Your router does not receive a reply to LCP echos x 6(normally). Bring PPP session down. It will try to reestablish PPP as in sync. If that fails router will resync to solve loss of IP connectivity not because of loss of sync as it is already in sync.

So where is all this dropping happening?

Somewhere inside WBC I am sure?
A LNS to Radius link maybe?
An ISP radius server /The ISP would fix that.

This generally happens at times of congestion in my case.

@aesmith . Have you got any more info on this. Logs etc.?

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ejs

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Re: ADSL2+ QoS and Day Time PPP Dropouts Without Retrain.
« Reply #25 on: May 08, 2019, 08:30:40 PM »

Without any monitoring of when CRC errors are occurring on the DSL link, it's not possible to know when stuff is being lost in transit over the DSL link. It's possible to have enough errors that everything, including what's keeping the PPP connection alive, will be lost, but without the DSL link retraining.
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DiggerOfHoles

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Re: ADSL2+ QoS and Day Time PPP Dropouts Without Retrain.
« Reply #26 on: May 08, 2019, 08:58:31 PM »

10 day training/stabilisation over. 6A to shed out with a Billion. Can report proper data then. Thanks.

It's possible to have enough errors that everything, including what's keeping the PPP connection alive, will be lost, but without the DSL link retraining.

Does this mean as long as SNR stays above 0dB all PPP control data can be lost causing PPP to reconnect when CRC errors reduce? 
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ejs

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Re: ADSL2+ QoS and Day Time PPP Dropouts Without Retrain.
« Reply #27 on: May 08, 2019, 09:04:40 PM »

Does this mean as long as SNR stays above 0dB all PPP control data can be lost causing PPP to reconnect when CRC errors reduce?

Yes, it's possible. Sometimes things will even stay connected with a negative SNRM.
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Weaver

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Re: ADSL2+ QoS and Day Time PPP Dropouts Without Retrain.
« Reply #28 on: May 08, 2019, 09:43:42 PM »

I have had many occasions with a number of Netgear DG834v3 modems where SNRM can momentarily go negative and they do not drop the dsl link, and PPP is completely unaffected. (The displayed text was hilarious, with integer overflow, until Netgear fixed the software to display something sensible for negative SNRM values.)
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DiggerOfHoles

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Re: ADSL2+ QoS and Day Time PPP Dropouts Without Retrain.
« Reply #29 on: May 08, 2019, 09:48:15 PM »

Yes, it's possible. Sometimes things will even stay connected with a negative SNRM.

I understand the -0dB thing I have observed it many times.

What I don't understand is how noise/interference/line fault can be so selective?

As CRC is ATM error checking and correction ......

I need to think about this one.
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