DSL "Crosstalk"

[ThomasM]

Hi all.

Firstly, please forgive me if any portion of this post betrays my ignorance about this topic. I hope that my message will be understood regardless!

I live in a rural area where the only available internet connectivity (bar satellite) is BT IPStream. I live around 30 meters away from my local exchange (EAWWR), and I have four lines, each serviced by IPStream Connect MAX Premium.

My sync rate on each line is the full 8192, and each line can independently achieve about 6.5 megabits per second real world performance.

The problem that I have is that the lines appear to interfere with each other. With all four lines maxed out, the performance of each line degrades to around 3 megabits per second. This also appears to change depending on unknown conditions - last weekend I was able to achieve 6 on all four simultaneously, which I was elated about, but the next day the problem reasserted itself.

Unfortunately, my ISP (PlusNet) tell me that they can't do anything about it for two reasons... 1) BT Wholesale don't have procedures in place to handle this kind of complaint, and 2) BT only guarantee 512k per line.

PlusNet have told me that the exchange is nowhere near capacity, and that contention isn't the cause (though it certainly does seem contended!).

So, I have two questions:

1. Can any of you take a guess at what might be the problem? Have any of you seen such an issue before?
2. Can I hire an engineer directly to sort it out, or am I obligated to go via my ISP?

I very much appreciate any advice you guys may have to offer.

Kind regards

Tom


Edit: I anticipate that this question may come up: Yes, I am bonding the lines, but it's not relevant to this problem because the issue has been found to exist without bonding - i.e, I tested each line separately in a completely isolated fashion.

[qasdfdsaq]

Are your modems resetting and disconnecting every time you use multiple lines simultaneously? If not then the line is not what is dropping to 3Mbps.

Either way you need to look at your modem readings to see your line information. That's the crucial information which is missing here...

[ThomasM]

Originally Posted by qasdfdsaq

Are your modems resetting and disconnecting every time you use multiple lines simultaneously? If not then the line is not what is dropping to 3Mbps.

Either way you need to look at your modem readings to see your line information. That's the crucial information which is missing here...

Hi qasdfdsaq, thanks for your response.

The modems are not disconnecting. I'm not at home right now, but from previous checks into this issue, the SNR on all four appears stable and decent, and I'm seeing very low errored packets. I will post the actual numbers when I get home tomorrow evening if it would be helpful.

I'd like to ask about this:

Originally Posted by qasdfdsaq

If not then the line is not what is dropping to 3Mbps.

What else might cause the problem? PlusNet wouldn't be intentionally contending my four lines, surely.

[qasdfdsaq]

Unlikely to be deliberate as you say, any contention on the Plusnet side would likely happen at a higher level.

If it were a case of link-layer interference between the lines I would expect to see modem disconnects and resynchronisation at the lower speed, which you've said isn't happening. So that really leaves the equipment at either end I suppose.

What are you using to bond the lines, and how are you testing the throughput (both combined and invididually)?

[ThomasM]

Originally Posted by qasdfdsaq

What are you using to bond the lines, and how are you testing the throughput (both combined and invididually)?

I reproduced the issue *unbonded* to ensure it wasn't an issue with my bonding solution (which happens to be SharedBand) - so the bonding itself isn't relevant.

Here's how I tested this:

1. Obtained four laptops.
2. Connected a laptop to each router (nothing else connected to the routers)
3. Commenced a 1gb download on the first laptop. 6.5mbit download rate
4. Commenced a 1gb download on the second laptop, both downloads slowed to approx 5mbit
5. Commenced a 1gb download on the third laptop, all three slowed to approx 4 mbit each
6. Commenced a 1gb download on the fourth laptop, all four now running at around 3.5 mbit/sec.

To eliminate the source site as a possible cause, I tried downloading from several other, large, well-known hosts and I saw exactly the same behaviour.

~Tom

[progers]

It certainly sounds like a contention or capacity issue to me

[qasdfdsaq]

Possibly, but contention or capacity issues would a) Vary by time of day and b) Be very unlikely to occur on this sort of scale.