Varying speeds to same house for different lines

Hi all - I'm wondering can help explain some of the factors why I'm seeing different line speeds between two different lines into my house. Here's some details;

Our house is on the edge of broadband availability - initially (~2001-2002) we couldn't get it at all. But then with line length availability changes we just got in.

Line 1 - installed when house was built in 2000. BT availability currently checker reports 0.5Mbps. We can get no more than 0.6 on connecting to master socket. Currently getting about 0.4-0.5. We have Sky as ISP and use this for home use (8Mbps package).

Line 2 - installed for home office in approx 2002. Line was originally installed as ISDN for voice and data. This was changed to broadband when availability checker started reporting ok. BT checker reports 1Mbps. We get at least 1.4, sometimes over 2. Currently getting 1.7 on master socket. ISP is BT Business.

The question is, obviously, what are the factors that can influence this difference between the two lines? Given where we are I'm very happy with 1.5-2Mbps - but if we get that on one I'd expect the same on the other. The wires must run the same length, through the same ducting, to the same cabinet?

Any insight much appreciated, thanks.

Wires don't necessarily run the same way although they are likely to. Pretty much all cables have joints in them so it could be that there are fewer joints on one line or that they are better quality or that they haven't corroded as much.

Also, quality of the wire may be different - faster line may have a slightly higher grade cable reducing the attenuation and noise pickup.

In the end there are so many possible reasons that one is better than the other that it is impossible to guess. Because of this BT don't generally try to sort these as they could end up replacing a whole line for a small difference (or no improvement at all potentially).

You may well think they run through the same ducts etc.. but not always.

So the length of the line is one thing.. and they may well be different lengths.
Another thing is placement of the pairs in the larger BT cables.

I had similar issue as to you.. and they were routed the same but one paid was in the middle of the cable and one was on the outside and they had different characteristics.

So there are just a few things that could differ.

You could try and order a new line.. then cancel the original.. but it depends what spare pairs they have.. plus it will cost you money.. and you may end up with a worse line.

When you tested at the master socket did you remove the bottom half of the faceplate?

Even if you did, it would still be worth checking that any extensions are properly connected via the faceplate and so were not affecting your tests. I could be that something as simple as removing the bellwire would bring the 2 speeds closer together.

Edited by deleted (Fri 12-Mar-10 15:03:32)

When you tested at the master socket did you remove the bottom half of the faceplate?

I can't remember doing so, so I'll try again and see if there's any major difference.

The simple answer is 'It's just the way it is'

The two pieces of wire are two separate wires and presumably several kilometres in length. That's ample opportunity for something to affect one wire that doesn't affect the other. In actual fact the wires probably aren't that long - there are probably at least a couple of joints in that length and maybe even some splices. So even assuming they go the same nominal route doesn't mean they will have the same characteristics.

It comes down to the luck of the draw and even much shorter lines can offer differing speeds. At our office one line manages nearly 4Mb/s - the other is closer to 1Mb/s.

You could try to get your ISP to send an SFI engineer out but tbh that process can be fraught and you can end up with a bill for a couple of hundred quid - possibly without seeing any benefit.

most likely to be the " e side " cable ( exch to cab / green box )

as a rule this is most of the cable run and as a rule there are 2 or more cables feeding a cab .

You need to post the line stats (Attenuation/SNRM/Sync) for both lines when connected to the BT TEST socket behind the faceplate.

This will show your lines best achievable stats and allow others to see how things are

Remember: BT Business has more Priority than normal connections (Contention Ratios are better on a Business connection). Also, if your exchange has been unbundled then the sky line will go to a different DSLAM at the exchange. Even if it hasn't it may still. This would mean that you are being served by 2 different DSLAMS.

Are any of the lines overhead? Weather conditions can affect overhead cables AND they can go in a totally different direction than Underground cables.

Edited by chris6273 (Sat 13-Mar-10 21:20:51)

Many thanks for the replies. I've tried connecting to the test socket and have the following stats;

Line 1 (Sky ISP) - Test Socket;
Connect Speed: 384kbps up - 429kbps down
Attenuation: 64.5db up - 39.2db down
Noise: 14.4db up - 10db down

Line 1 - Extension Socket;
Connect Speed: 383kbps up - 409kbs down
Attenuation: 65db up - 39.7db down
Noise: 7.7db up - 12.0db down

After this I checked on my Sky broadband account details online. They say they 'tested' my line recently (January) and;

"Your connection has been set to a download speed of up to 0.4Mb (384Kb)"

Which seems to match the speeds I'm seeing. This seems like they're capping me to get a reliable service level. Before they tested my line, I could see varying speeds up to .8Mbps, but there were drop outs at times. This speed limit seems a little ironic when Sky themselves say that they have 'No speed caps on our network', but I understand they have to juggle reliability with speed. However, at this speed the service is hardly worth having - and I'll likely use other methods to connect (see below). I've not tried removing the ring wire because if Sky are fixing my max speed anyway, there's seems no point trying.

Fyi - the other line stats are;

Line 2 (BT Business) - Test Socket;
Connect Speed: 2144kbps up - 448kbps down
Attenuation: 55db up - 15db down
Noise: 9db up - 21db down

Line 2 - Extension Socket;
Connect Speed: 1856kbps up - 448kbs down
Attenuation: 56db up - 15.5db down
Noise: 10db up - 20db down

So, this just shows what is achievable to the house, but as I've learnt from the replies, there are many factors that apply for different lines; joints, position of cable in bundle or street ducting, E or D-side connections, exchange DSLAM connection for LLU. Comparing stats on Line 1 and 2, it's clear that Sky wouldn't be able to provide me with the same speed level anyway.

Later this week I'm getting the BT Business line upgraded to VDSL through FTTC. Hence I'm trying to find out the reasons for inconsistency while I still have the ADSL to compare it. As my new VDSL hub is 802.11n, this should allow me to get better wireless coverage across the house and utilise the much higher speeds throughout (which has been a problem using 802.11g up to now). I think I'll try running everything through the VDSL, and if it all works out drop the Sky broadband.