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[kitz]

A simplistic view is that a line card as an equivalent to an ethernet network card in your PC.  Line cards slot into the DSLAM or MSAN (which is the excahnge equivalent of your router).  These are simplistic views though since a typical MSAN line card will control up to 64 connections (the dslam has a switch hub)  and they obviously cost a heck of a lot more than the typical network card.

Theres photos of the equipment on the main site under How adsl works in the telephone exchange.

As to the line card causing the latency... hmmm not sure about that... all the newer type BTw DSLAMs and MSANs perform low level QoS so that even a stressed out VP doesn't show increased latency.  Even back in 2003 when we had real exchange problems on a VP, and there were  30+ of us affected and complaining via various ISPs... not one of us saw any increased latency.  Even on heavily congested DSLAMs over many years Ive never, ever  seen any recorded increased in latency because BTs DSLAMs are QoS'd to ensure this doesn't occur.

What I have seen several times though, is increased latency occurring when the VPs ATM cloud mapping seems to have gone screwy..  and its almost like the ATM cloud routes traffic up via Edinburgh then back down to Devon before hopping onto the main Colossus backhaul.  When this happens it can literally double your latency times.
I'm not sure where this occurs exactly but its something I think to do with the RAS or something controlled at the RAS.
(See BT IPStream Network).

On the occasions that Ive seen it, it has normally happened when BTw have been undertaking some form of work on the DSLAM VPs and have usually followed a change of RAS routing.  I'm not saying this is the case with you, but it does seem a possibility, far more than a line card issue.
Particularly in view of the fact that BTw are reviewing their routing as part of the 21CN upgrades.

-------------------
One other thing to note

>> 40 ms    40 ms    39 ms  213.130.147.57

The problem is occuring somewhere before at 213.130.147.57 which belongs to Netservices.  Fast dont have their own centrals and use NetServices, so this could be another place where the problems are occuring.

[dpd]

thanks very much for that kitz. i had no idea that it was as compex as that. i have read the articles that you supplies in your post which were most informative even if at times i was a bit confused and baffled to say the least. heres me thinking it was a straght forward case of broadband from my isp>bts equipment>to my exchange>to my house. 

how stupid do i look now eh ?

anyway the problem is still with bt and we are just awaiting there response. a pattern which has become clear is that between around 9am - 3pm my ping times are ridiculously varied. after which time they return to about 40ms which is still twice what they should be but appear stable. this morning i pinged bbc.co.uk and got this:

C:\Users\david>ping bbc.co.uk -t

Pinging bbc.co.uk [212.58.254.252] with 32 bytes of data:

Reply from 212.58.254.252: bytes=32 time=58ms TTL=249
Reply from 212.58.254.252: bytes=32 time=146ms TTL=249
Reply from 212.58.254.252: bytes=32 time=59ms TTL=249
Reply from 212.58.254.252: bytes=32 time=57ms TTL=249
Reply from 212.58.254.252: bytes=32 time=66ms TTL=249
Reply from 212.58.254.252: bytes=32 time=53ms TTL=249
Reply from 212.58.254.252: bytes=32 time=64ms TTL=249
Reply from 212.58.254.252: bytes=32 time=63ms TTL=249
Reply from 212.58.254.252: bytes=32 time=67ms TTL=249
Reply from 212.58.254.252: bytes=32 time=64ms TTL=249
Reply from 212.58.254.252: bytes=32 time=61ms TTL=249
Reply from 212.58.254.252: bytes=32 time=46ms TTL=249
Reply from 212.58.254.252: bytes=32 time=55ms TTL=249
Reply from 212.58.254.252: bytes=32 time=62ms TTL=249
Reply from 212.58.254.252: bytes=32 time=61ms TTL=249
Reply from 212.58.254.252: bytes=32 time=163ms TTL=249
Reply from 212.58.254.252: bytes=32 time=60ms TTL=249
Reply from 212.58.254.252: bytes=32 time=60ms TTL=249
Reply from 212.58.254.252: bytes=32 time=61ms TTL=249
Reply from 212.58.254.252: bytes=32 time=65ms TTL=249
Reply from 212.58.254.252: bytes=32 time=53ms TTL=249
Reply from 212.58.254.252: bytes=32 time=60ms TTL=249
Reply from 212.58.254.252: bytes=32 time=60ms TTL=249
Reply from 212.58.254.252: bytes=32 time=57ms TTL=249
Reply from 212.58.254.252: bytes=32 time=56ms TTL=249
Reply from 212.58.254.252: bytes=32 time=65ms TTL=249
Reply from 212.58.254.252: bytes=32 time=51ms TTL=249
Request timed out.
Reply from 212.58.254.252: bytes=32 time=58ms TTL=249
Reply from 212.58.254.252: bytes=32 time=53ms TTL=249
Reply from 212.58.254.252: bytes=32 time=59ms TTL=249

as you can see the times are all over the place so after reading the info kitz gave me i do think the explanation about re-routing to opposite ends of the country is a viable reason. also if this proves to be the case is it an easy fix which can be done quickly or is it worse case scenario?

thanks for the help and info lads.
regards david

[kitz]

>> a pattern which has become clear is that between around 9am - 3pm my ping times are ridiculously varied. after which time they return to about 40ms which is still twice what they should be but appear stable.

Have you just taken those now?  They are even higher!

latency which varies at certain times of the day is often more likely due to congestion.   
If they stabilise in the evening then this could be a result of this is often when the ISP turns on some form of management to ensure that certain types of traffic get priority.

You may also be interested in a couple of tools on this page such as pint plotter and WinMTR
http://www.kitz.co.uk/links/network_tools.htm

[dpd]

just an update. after almost 10 days im still waiting for bt to come back to us with a solution to my problem. my isp have been in touch to let me know but there is no news. how long does it normally take for bt to look at problems?

[kitz]

hmmmm not good.. and imho they are perhaps stalling :/

[dpd]

well after 2 weeks of the fault being raised with bt still nothing is happening. my provider who have been helpful and in regular contact have now said that it has been esculated further with bt to try and reach a fix. this is really not good as i too now suspect that this is now stalling tactics by bt. surely after 2 weeks something should have happened.

[silversurfer44]

When dealing with BT you need plenty of patience and tenacity see my post 'At Last' and you will see what I mean. Hopefully yours will be sorted sooner.

[dpd]

just an update.

bt have been in touch this morning and said that they have replaced the line card i was on and to retest in 24hours and i should hopefully see a difference. great news eh? well i thought i would check my router stats but it says that there has been no drop in connection since i last rebooted. i may be wrong here but if they have done as they say surely there would have to be a disconnection at some point? like i say i may be wrong but was hoping someone may be able to offer some advice on this.

[kitz]

correct - a change of line card would involve a disconnection... it often involves a short period of time without any connection at all :/
A full lift and shift to another line card/dslam can take anything from 10mins to half an hour.

[dpd]

just confirmed what i was thinking. i would really just appreciate some honesty and be given a true picture so im aware of whats going on. but even the good old value of honesty is missing in this modern tech era. i have emailed them back to let them know that no disconnection has taken place so how can they have replaced a line card. be interesting to hear what they say......

[waltergmw]

Hi dpd,

Pardon my crudity but it's called pissing against the wind ! I.e. you'll be very lucky to get anything of value back.

Kind regards,
Walter

[dpd]

yeah i thought so myself mate. whenever dealing with companies like this its always the same. kicking and screaming and pulling teeth out just to get somewhere. i appreciate that im only 1 single person and to bt they dont give 2 hoots about me but it would be so refreshing and innovative for bt to actually try to rectify faults within a specific time. no bull**** but just a timescale and a fix. but then again this is the real world so its a case of cat and mouse.

[dpd]

ok i have an update from bt. they say that the replacement line card was done 48 hours ago. which was before my last reboot. the problem i have is why wait 2 days to tell me to test in 24 hours. something smells very fishy here. is this standard practice or am i right to be suspicious?

[waltergmw]

Hi again dpd,

I think you have every right to be a little suspicious.

Upon occasion BT can be absolutely first class at isolating and fixing problems.
Upon other occasions you can be far less fortunate.

If your conditions have not changed, despite their assurances, then you need the patience of a saint, ask for an e-mail addess to send your data, and politely tell them to escalate the problem to their line manager and try again.
(BT probably don't need to see your data but if you say you have Routerstats data recorded they will realise that you have some understanding of the horrors (magic ?) of ADSL technology.)

Kind regards,
Walter

[dpd]

i have a little knowleadge about it but only through reading these forums and reading other info from the net but know enough to know when i am being led up the garden path. fortunately my isp support team are dealing with it for me and are conatantly in touch with bt and also let me know whenever they have any update. i have to say fast.co.uk support have been great. since the last post they have also sent me another update which says it looks like a card change has been done as i now have a different CBUK reference code for the circuit im on. suppose i will just have to retest tomorrow morning and i will let you guys know what happens.