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Author Topic: bRAS profile - my experience  (Read 5006 times)

kitz

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bRAS profile - my experience
« on: January 01, 2007, 10:11:54 PM »

Thought I'd share a personal experience of bRAS profiling that seems to go against all that BT say should happen.
Bear in mind this is a 7dB att connection which has always sync'd at 8128 with an SNR Margin of around 14dB

---------------

On Sat evening I lost all my downstairs lighting - so trying to be efficient I replaced the fuse in the fuse box.  Duly armed with re-wired fuse I plugged it back in and BANG..  I temporarily lost power in the whole house.

Reset the master switch and everything came back up again aside from the lighting....  and my router.
Whilst waiting for someone to come to my rescue.. I tried to see what could be done about getting my router to resync to the exchange.
After about an hour it did...  but with disastrous results...  synced at 8000, lost sync.. sync at 7800, loose sync..  and downwards.. it went until by the time it got to around 4000 I gave up and unplugged it.

Anyhow chris came round - fixed the faulty light switch and turns attention to the router.. which is still having problems trying to sync.
Still the downward trend to 4000 ish with only 6dB Margin.
Was about to get the SAR out, when a final router reset managed to at last get a stable resync of 8128.

Do a BT performance test - IP profile set at 5000. :/
So me thinks thats me buggered for the next 3 days and interleaving.

However..  next day checks my IP profile and back up at 7150..  so what happened here seems to go against all the so called rules laid down by BT as to bRAS profiling.

~ It didnt take long for the lower IP profile to kick in.
~ Blip logic wouldn't have been applicable in this case because sync was down more than once and for more than a couple of hours in all.
~ Blip logic didnt kick in anyhow or I wouldn't have been lower profiled in the first place
~ IP profile set at 5000 despite me syncing at speeds that should in theory have profiled me at 3500
~ It didnt take 3 full days to see the increase back up to full sync speed (possibly 12 hours?)
... and thankfully I'm on FAST and don't have to play ISP <--> BT ticket tennis trying to get interleaving turned back off.
« Last Edit: January 01, 2007, 10:14:53 PM by kitz »
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roseway

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Re: bRAS profile - my experience
« Reply #1 on: January 02, 2007, 07:41:19 AM »

That's certainly a weird series of events. You do hear occasional reports of IP profiles going back up almost immediately instead of waiting for three days (in fact it happened to me once) but the 5000 profile after syncing at 4000 is really quite odd.
Also odd is the behaviour of the router after the mains problems. Routers do seem to be very sensitive to mains glitches (cheap and nasty power supplies I presume) but I have no idea why they sometimes take so long to recover. I can't imagine what the 'healing' process is.

Eric
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kitz

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Re: bRAS profile - my experience
« Reply #2 on: January 02, 2007, 03:45:04 PM »

>> You do hear occasional reports of IP profiles going back up almost immediately instead of waiting for three days (in fact it happened to me once)

Yes Ive seen this too... in fact I am beginning to wonder if its a "first offence" then the going back up could happen a lot quicker than for repeat offences...  All unproven - but something doesnt seem to be happening quite by the rules set out by BT.
I also synced in the 4000 region on at least 2 separate occasions with at least an hour in between, but it didnt seem to pick up on those.

Something for sure upset my router -despite it being plugged in to a power surge protected socket.
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kitz

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Re: bRAS profile - my experience
« Reply #3 on: January 02, 2007, 03:48:09 PM »

BTW whilst on weirdness things occuring totally unrelated but several weeks ago I had a weird event occur with my latency.
I'd been doing a fair bit of testing which involved several reboots of my router... when all of a sudden my latency increased drastically.
My normal bbc pings of 16ms increased to nearer 40ms.

For 3 days solid latency I had an additional and rock solid additional 24ms added - no matter where I pinged. 
The problem only seemed to affect me and no-one else from my ISP.. although my router still reported me on FAST mode.

You can see the sudden increase and decrease on these l8nc graphs
(ignore the blue on the increase as I was downloading something at the time), but you can still clearly see the underlying yellow increase.
BT works in mysterious ways - perhaps it was a routing issue and for 3 days my connection went up via aberdeen and then down to devon before going on to london.  :-\


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roseway

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Re: bRAS profile - my experience
« Reply #4 on: January 02, 2007, 06:51:07 PM »

That increase in latency does rather suggest that you had been interleaved temporarily, despite what the router reported. In theory that would have limited you to 7150kbps sync, but several people have reported full-speed sync after interleaving, so that rule isn't inviolate either. But you could also be right about routing of course. :-\

Eric
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mr_chris

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Re: bRAS profile - my experience
« Reply #5 on: January 03, 2007, 04:14:15 AM »

Just to correct you on a small technicality, the alleged limit when interleaved is 7616kbps, not 7150kbps (7150 is actually the IP profile speed for an 8128kbps sync speed, which is probably where you've got it from).

And yes, I am living (altho i can't sleep, so dont feel very alive at the mo) proof of having been interleaved and synced at 8128kbps.... occasionally!
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roseway

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Re: bRAS profile - my experience
« Reply #6 on: January 03, 2007, 07:53:32 AM »

Just to correct you on a small technicality...

Ah yes, I've fallen prey to the old adage "Post in haste, repent at leisure". :-[

Eric
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browolf

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Re: bRAS profile - my experience
« Reply #7 on: January 05, 2007, 12:51:17 PM »

my router has reported a sync of 7904 and 8128 on interleaved. is it lying?

ive noticed when i've had sync problems that the sync can be all over the place and doesnt seem to follow any obvious pattern
like a period of 30mins once when it went from
576 > 0 > 4876 > 1760 > 3296 > 2144 > 0 > 2244 > 0 > 5408

the zeros are loss of signal
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roseway

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Re: bRAS profile - my experience
« Reply #8 on: January 05, 2007, 04:51:10 PM »

No, I don't think your router is lying. It's not supposed to sync above 7616 when it's interleaved, according to BT, but reports that it does happen are not uncommon.
When your sync is all over the place like that it suggests a significant problem with your line, and if the problem is only temporary it's quite likely to be weather-related (rain or wind). If the ADSL is affected by using the phone it could be a filter problem or a high resistance fault on the line.

Eric
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browolf

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Re: bRAS profile - my experience
« Reply #9 on: January 06, 2007, 05:56:48 PM »

yes but even with a problematic line you'd think sync mechanisms would try and follow some sort of pattern. of course i could be missing vital information only picking it up every 60 seconds. i supoose you'd need more real time monitoring to discern a pattern. it even possible the router isnt checking often enough either...

its like trying to reverse engineer the software at the exchange by how our non-scientific-instrument routers behave lol




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kitz

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Re: bRAS profile - my experience
« Reply #10 on: January 08, 2007, 10:50:31 AM »

This is pure speculation and not anything proven, but I sometimes wonder if things like this may have something to do with the kit at your particular exchange.

Now Im not sure if this will apply to max - but the theory is still there.
But "back in the old days" of fixed adsl when speeds were a lot more static and you could spot certain things easier, but there were definately some exchanges which seemed to allow "a bit extra" to cover atm overheads, and this affected your max throughput speed.

Chris noticed this when he moved to a neighbouring exchange and it affected the maximum throughput speed no matter how he tweaked etc with the same kit and router. When we were both on the same exchange despite being on different ISPs at one point - the maximum throughput speed was always the same within 1 or 2kbps

Something else I noticed when on 2Mb during summer 2005 and running up to max there were times when I could very often get speeds of up to 1900 on the AG speedtester with 1700kbps being quite common.
These speeds were supposed to be impossible for a 2272 sync but it happened way too often for it to be a fluke.  I also used to see other people on different exchanges reporting the same thing - and there was definitely a period when quite a few users were reporting  more than the theoretical max throuput of 1920 kbps that should be possible on a 2272 sync.

It would therefore seem, that no matter what the rules should be..  there sometimes is some exceptions to these so called BT rules.... or I could be talking just pure rubbish.

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Edited to add

Despite what BTw "say" it is possible to attain a sync of more than 7616 kbps on an interleaved line.
This is dependant on both the DSLAM and your router being able to support S=1/2 mode which effectively combines two RS code words into a larger logical code word of 510 bytes (ANSI T1.413), and there being sufficient spare SNRM.
« Last Edit: October 14, 2008, 11:03:43 PM by kitz »
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