A Tale of Two Lines

We have two phonelines at this house, both broadband enabled. One sings, the other croaks ;-) I'm interested in any hints-n-tips as to (a) whether there's any reasonable reason, (b) which ISPs are good at kicking BT into taking action.

We're stuck with BT as provider for the last 3.5km or so - line-of-sight to exchange is only about 1.8km, but scenic location - other side of the Avon Gorge to the Bristol West exchange in Clifton - means copper distance is as stated. LLU available from some (Be, Orange, Sky/UKOnline), not currently signed up with any of those, so using BT Wholesale products as resold.

On the Good line, we're signed up with Nildram. Used to have Office 500 (512kb fixed) until early 2006, went MaxADSL with them and have had reliable connections at about 3.5Mb/s. Specific stats for this line go thus:

Us Rate (Kbps) 448
Ds Rate (Kbps) 3936
US Margin 18
DS Margin 4
Trained Modulation GDMT
LOS Errors 0
DS Line Attenuation 54
US Line Attenuation 31
Peak Cell Rate 1056 cells per sec
CRC Rx Fast 0
CRC Tx Fast 0
CRC Rx Interleaved 25609
CRC Tx Interleaved 101
Path Mode Interleaved

(That's for a 3-day-old session. Hardware currently on that line is an el-cheapie Safecom/Guru GART2-4115, as on sale at eBuyer for a stupidly low 15 squids all in; have had similar sync-n-stats on this line from a Zyxel 623R for most of the year.)

pauses to link posting machine up to the Other line

The Other line is currently subscribed to Virgin, who claim to be unable to ADSL-Max it. It syncs without any hassle at 512kb, and though the downstream attenuation is a horrible 10dB bigger than the Good line (65dB instead of 54dB), there's oodles of noise margin (22.5dB). Here are the stats from the Zyxel currently driving that line:

Upstream Speed: 288 kbps
Downstream Speed: 576 kbps
Node-Link Status TxPkts RxPkts Errors Tx B/s Rx B/s Up Time
1-PPPoA Up 727243 854277 0 0 0 74:26:50
relative capacity occupation: 29%
noise margin downstream: 22.5 db
output power upstream: 11.5 dbm
attenuation downstream: 65.5 db

The BT Broadband Availability propagandal reflects these disparities in d/s attenuation - the Good one says 'good for 2Mb fixed, expect maybe 3Mb on MaxADSL', while for the Bad one it says 'ADSL Max at 250kb, maybe better if you're particularly lucky, sunshine'.

So, here's the mystery: the lines come from the same exchange (albeit one having an 0117 923 prefix, the other 0117 973... but That Shouldn't Make Any Difference, right? ;-) They follow the same tortous route from exchange to property, both come in to pukka BT master sockets with front-plate splitters (so all the steam-radio/POTS gubbins is separated from the ADSL goodness at what our US cousins would call The Demarc); further POTS extensions run round the house in 'old' stylie for the Good line as well as up to the Cat5 patch panel in the loft, and only via the patch panel in the loft for the Bad line - separate Cat5 runs for the filtered and unfiltered runs - after all, if you've got the wiring, you may as well use it... No change in stats when using test-socket-only connections on these lines. I'm not (quite ;-) rude enough to BT's circuits to swap over the pairs at the old-style BT junction box where the two BT pairs go from external drop wire to internal wiring, to eliminate the few yards of internal pre-master-socket wiring as the culprit.

My suspicion is that the routing relatively close to our house - maybe the underground stretch from the bottom of the pole in the verge to the green box at the top of the hill - is rather flaky: we've had a couple of line faults of the 'crackly voice quality and dretful broadband' variety in the last couple of years, most recently on the Good line, now restored by BT. The relevant issue for me is whether there's any chance of getting BT to trace a reason for the big difference in attenuation and performance - annoyingly, Virgin's current response to my 'please MaxADSL it' request on the Bad line is 'no speed upgrade for you, sunshine'. I'm toying with the idea of going LLU to (shudder) Orange, say, on the Bad line, just as a way of getting that early pre-sales enthusiasm (?) working for me. But I'd be interested in any comments the experienced contributors here have on
- what technical reasons there could be for the large difference in performance between the two lines
- what else I can do as a mere Customer (albeit with a clue or two) to diagnose the cause
- which ISPs, whether BT Wholesale resellsers or LLU types, have a good record at enthusing BT to sort out 'but it could be so much faster' issues rather than the more prosaic 'line's gone dead' faults.

(Sorry for the length of this first post, but hopefully it's all relevant info!).

Thanks in advance - Stefek

There is obviously a physical difference bteween the 2 lines. It seems that you have proved the difference is not due to your wiring (I say seems as I didnt read all of that bit properly), so must be due to the external line, unless your router(s) are giving false readings.
There are simple reasons for this such as different cables utilisied for each line or a poorer section somewhere, but broadband is basically "best efforts" as far as BT is concerned, meaning
they are not going to improve one line just to get a faster line speed. If it were actually faulty then they would of course investigate it, and maybe in the course of fixing it (hopefully) they might improve it but you dont stand much if any chance of them pro-actively coming out.

the less good line says

relative capacity occupation: 29%
noise margin downstream: 22.5 db

so no reason that shouldn't go onto Max to get more speed with a more cooperative ISP. Should go 2-3 times as fast as now.

Reasons for potential differences apart from longer routings include thinner gauge copper, more joints, poor joints, aluminium etc.

You should get the attenuation off both with the same kit, as a cross-check.

Thanks for confirming my suspections that the less good line oughter be capable of doing better even with the high attenuation it currently has. I'll see if I can find an ISP who'd be interested in kicking BT Wholesale gently on my behalf.

I have had both modems on both lines, and they do give similar figures- will do a cross-check again just before opening negotiations with ISPs. The el-cheapie Guru makes switching lines less hassle through being able to store and recall multiple ISP profiles (username, password, and AFAIR also the black magick of VCI, VBR/CBR, and similar incantations), though it's hardly a massive effort to type 'em back in to other modems.

Thanks again, and I'll try to remember to post back here if I get a resolution (cue hollow laughter from the experienced ;-) - Stefek

In reply to:

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'll see if I can find an ISP who'd be interested in kicking BT Wholesale gently on my behalf.

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You just need one to place a regrade order, there is no kicking required.

In reply to:

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You just need one to place a regrade order, there is no kicking required.

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Straying outside the 'technical': a follow-up email to Virgin asking for this, again, emphatically and pithily, met with no response. The call to Cancellations in aid of getting a MAC code caused me to talk with someone who magically found it possible to place a regrade order after all; it's allegedly In Progress, with Max'ing due within the week. We'll see what sort of stats and rate we settle on. (I have about 6 weeks left of my initial 12 months with Virgin, and it's Mandatory MAC-Code Day in just over a month, so I'm happy to let them take the strain of the regrade before hopping over to Namesco or similar).

Thanks for your help and encouragement - Stefek

MaxADSL enabled today on the lower-quality line: ah, the magic of calling the Terminating The Account team! As foretold by resident expert here, and in line with other MaxADSL informed info, it's given a useful speedboost. Right now it's just starting its 10-day dance (and given the foul weather, the BRAS profile will include lass than flattering figures...); but I've had a sync at 2304/448 and then at 2176/448. Will let you know in 10 days' time what the settled rate appears to be, if I remember!

Once again, thanks - Stefek

Well, we've now had 10-11 days of MaxADSL running on the "poor" line - 63dB attenuation, 6dB noise margin. Virgin's initial reluctance to go to MaxADSL notwithstanding, I've synced repeatedly at line speeds within a gnat's whisker of 2.3 Mb/s, with one exception early on (around 1.8). Sessions have stayed up for 48hrs plus.

Well worth doing! Over and out - Stefek