2 x ADSL with 2 different speeds

HI
First post for me on here, so please go easy

I have had Sky broadband unlimited now for 2-3 eyears and have always had around 3mb to 3.5mb download speeds.

About 3 months ago i added a 2nd ADSL line from BT, and have been getting speeds of around 2.5mb to 3mb speeds.

however in the past month my BT line has stayed the same speed but my Sky speed has dropped to 1mb - 1.5mb

I have contacted sky and even had an engineer out, but they cant find anything wrong?
The BT engineer suggested that the only thing they could do was maybe run a new line to the property, but there was no gaurantee that this will work?

The drop in speed happend over night and was not gradual, has anyone any ideas?

the 2nd line in my house seems to piggy back the first line can this be done, could this be an issue?

Any assistance would be great.

I was not around when the engineer came to the house so I could not ask him any questions.

Thanks

Hi,

I actually have exactly the same problem. I had two telephone lines supplied by BT and used one of them for broadband with Virgin, which I used to get a constant 2.4 Mbps. Our exchange was recently unbundled so I used the second line to go with Sky and changed to BT on the other. This gave us better usage when the kids were at home!!

Both lines were on a consistent 2.4 Mbps day and night until recently when the Sky one dropped and now fluctuates to as low as 0.6 Mbps at any time of the day, despite being connected at 2.8 Mbps. It is impossible to use the new Sky Go as it is constantly buffering. I was always able to stream easily up to this point. I now have to wait at least an hour before I can watch an Anytime plus movie whereas before it used to be about 2 minutes.

I have changed channels, swapped filters, unplugged all other equipment and still the problem exists. Could Sky have a problem at their end as it would seem I am not alone.

The piggy backing is not a problem apparently, as I did originally have problems with my one line and asked this very question, but told categorically that it isn't so.

The BT line is still absolutely constant at 2.4 Mbps with hardly any variation at any time.

What makes it worse is that when i ordered sky originally it said that i could go on their Sky Unlimited package, which i took and have been using fine.

However when i go on to Sky and run a line check to see what speed i can get it says 0.8 to 4.5 however it then says i can only get Sky Connect as i am out of the sky unlimited area?
If i run the same check on the BT line it says 2 to 5 and I am ok to use Sky Unlimited?

am i over reacting or is there something not right?

In reply to a post by actionorton:

however in the past month my BT line has stayed the same speed but my Sky speed has dropped to 1mb - 1.5mb

I have contacted sky and even had an engineer out, but they cant find anything wrong?
The BT engineer suggested that the only thing they could do was maybe run a new line to the property, but there was no gaurantee that this will work?

The drop in speed happend over night and was not gradual, has anyone any ideas?

In reply to a post by actionorton:

am i over reacting or is there something not right?

Please post the full router stats (connection speed, attenuation, noise margin, etc.) from both lines.

It could be the two lines are different (maybe one has a lot of aluminium in the cable, or takes a different route back to the exchange).
It's also possible the different speeds are the result of nothing more than different 'target margins' on the two lines.....If one is aiming for 6dB, yet another is at a higher margin, they will connect at vastly different speeds.
It could also be a line fault, or maybe there's more internal phone wiring (in your home) on the lower speed line.

It could be anything, but let's start with the router stats.

As adebov says the router stats will be useful. See http://kitz.co.uk/adsl/frogstats.php for guidance.

They may also reveal which Sky product you are really on.

Hi Adebov

here are the details for both lines.

BT Home Hub 3
ADSL Settings
VPI/VCI: 0/38
Type: PPPoA
Modulation: G.992.3 Annex A
Latency type: Interleaved
Noise margin (Down/Up): 3.5 dB / 6.0 dB
Line attenuation (Down/Up): 55.8 dB / 31.9 dB
Output power (Down/Up): 15.3 dBm / 12.6 dBm
FEC Events (Down/Up): 318171295 / 2122
CRC Events (Down/Up): 520828 / 194
Loss of Framing (Local/Remote): 0 / 0
Loss of Signal (Local/Remote): 0 / 0
Loss of Power (Local/Remote): 0 / 0
HEC Events (Down/Up): 292464 / 232
Error Seconds (Local/Remote): 99146 / 256


Sky Unlimited
Netgear Router
System Up Time 17:01:53
Port Status TxPkts RxPkts Collisions Tx B/s Rx B/s Up Time
WAN PPPoA 1575 1451 0 4 7 17:01:03
LAN 10M/100M 3894 0 0 9 0 17:01:50
WLAN 11M/54M/108M 6878 18409 0 23 13 17:01:42


ADSL Link Downstream Upstream
Connection Speed 1333 kbps 510 kbps
Line Attenuation 59.5 db 39.2 db
Noise Margin 9.3 db 10.0 db

OK; the two lines are about the same length (assuming the Sky one is using ADSL2+, which general gives a line attenuation a few dB higher than the same length line using ADSL1 or ADSL2).
The BT line is using ADSL2 (G.992.3 is ADSL2; G.992.5 is ADSL2+).
Quite often, with lines of this length (it's probably around 5km long) modems will connect at a slightly higher speed on ADSL2, rather than ADSL2+.

Reason 2 is the Sky line has a noise margin of 9dB, compared to 3dB (although the target is probably 6dB) for the BT line.
This will produce a speed difference of around 1Mbps (give or take maybe half a meg).

You haven't posted the connection speed for the BT line in the stats, but I assume it's the faster of the two.

I'd ring Sky and ask the to put you on a 6dB "target noise margin", which should go most of the way towards equalising the speeds.

Also remember the routers will connect at the fastest possible speed which produces a noise margin equalling the target, so with the same target and re-syncing at the same time should produce similar speeds.
Anything else (either different targets, or syncing one line at night and the other during daylight) will produce different connection speeds.

Edited by adebov (Sun 28-Aug-11 16:28:50)

In reply to a post by adebov:

OK; the two lines are about the same length (assuming the Sky one is using ADSL2+, which general gives a line attenuation a few dB higher than the same length line using ADSL1 or ADSL2).
The BT line is using ADSL2 (G.992.3 is ADSL2; G.992.5 is ADSL2+).
Quite often, with lines of this length (it's probably around 5km long) modems will connect at a slightly higher speed on ADSL2, rather than ADSL2+.

Reason 2 is the Sky line has a noise margin of 9dB, compared to 3dB (although the target is probably 6dB) for the BT line.
This will produce a speed difference of around 1Mbps (give or take maybe half a meg).

You haven't posted the connection speed for the BT line in the stats, but I assume it's the faster of the two.

I'd ring Sky and ask the to put you on a 6dB "target noise margin", which should go most of the way towards equalising the speeds.

Also remember the routers will connect at the fastest possible speed which produces a noise margin equalling the target, so with the same target and re-syncing at the same time should produce similar speeds.
Anything else (either different targets, or syncing one line at night and the other during daylight) will produce different connection speeds.

Generally sky will not work with 'target noise margins'

They prefer to apply a sync speed cap.

Obviously it works in the same way.

E.g. if sky see the line is performing badly and is currently synced at 5 meg...

With most ISPs the target noise margin is increased from 6db to 9db

With Sky, instead they place an artificial cap on the line at say 3.5 meg. The line cannot sync higher than this unless Sky increase the cap. Even if you 'force' the noise margin down with custom firmware it will not go higher.

Generally this means that if you sync at 7pm you get a 3.5 meg speed.

Sync at 10am, still 3.5 meg.

If you sync at 10am the noise margin might be 11db when you sync, with a 3.5 meg sync

at 7pm, you still sync at 3.5 meg, however the noise margin may only be 8db

The difference is the noise margin isn't a 'target' as such. The only thing Skys DLM is concerned with is sync speed. Same goes with customer services, they will increase the sync speed cap, but not the noise margin target generally.

EDIT: obviously lowering sync speed increases the noise margin naturally.

Edited by ukhardy07 (Sun 28-Aug-11 17:01:51)

Strange cap (1333kbps) and just a coincidence the margin has turned out at 9dB I guess.
Surely such an unusual sync speed (1333kbps) can only be a result of syncing according to a target margin?
I'd understand if the sync was 1250 or 1500, but 1333kbps???

If you logon to mysky.sky.com, the link for My Broadband will say what package you're on.

Looks like you're on Sky Unlimited but your connection is suffering with noise from the other BT broadband.

You really need to ask sky to uncap your line and put you on the gaming profile and see if they will put you on g.dmt or ADSL2 instead of ADSL2+, or see if the router will let you choose that.

In reply to a post by adebov:

Strange cap (1333kbps) and just a coincidence the margin has turned out at 9dB I guess.
Surely such an unusual sync speed (1333kbps) can only be a result of syncing according to a target margin?
I'd understand if the sync was 1250 or 1500, but 1333kbps???

My lines set to 15.0 mbps however I sync at 15562 kbps, give or take a few kbps. it never syncs dead on a speed.

Sometimes, although rarely this occurs...

DLM sets the line to a sync speed e.g. 7mbps.

If the person syncs in the morning, they can easily get 7mbps with a 6 / 7 db noise margin

However in the late evening, their noise margin drops and is 4 / 5 db at 7mbps.

If they connect at this time they will sync below 7 mbps.

This is because sky does not allow a user to connect at a speed which results in an SNR below 7db (I'm pretty sure sky use 7db noise margin instead of the standard 6db)

The point is they could not sync above 7mbps even if they tried to force their snr down to 1db with custom firmware.

HOWEVER...

In the above case, if they are syncing below the cap that DLM has set. Manually lowering the SNR will increase the speed, but only upto the physical cap.

So yep, noise margin targets are in place to some degree. However the target is never usually set above 7db, if the lines unstable a sync speed cap is applied that increases the noise margin naturally.

So people often sync with an SNR of 10db, 11db etc.

So yes. I would say it's a coinsidence.

If you ring up sky they CAN apply a higher SNR target although they are VERY reluctant to do this.

If you login to your my sky account you can see what speeds your line has been set to. Often you can sync around 0.5meg higher than the speed in mysky as it's generally a rounded figure.

EDIT: The user can ring up and ask sky to UNCAP the line. This removes any artificial speed cap that has been placed on the line

In this case the line will sync at whatever speed a 7db noise margin gives.

So this CAN occur like you suggested, however DLM does not automatically apply it.

Edited by ukhardy07 (Sun 28-Aug-11 18:18:17)

All

Thank you for you great reponses, still trying to get my head around things.

One thing i picked up on was Batboy saying that the BT line may be causing noise on my Sky line? is this a possibility?

when i first moved in to my house the line was slow until i had the bell wire removed from my line. this increased the speed dramaticly.

The whole reason i had the 2nd line put in was so i could have twice the speed i had before, but at the moment i seem to have the same if not less between the 2.

First thing, i will call sky and ask them to uncap and see what happens.

Thanks

Yes, crosstalk between the two pairs of wires. If they refuse/don't understand uncapping, ask for the Gaming profile to be applied.

If crosstalk is suspected, then can be checked for

1. Unplug one modem, wait 30 minutes or so, and restart the remaining modem and see if its sync changes for the better. If around the same then no serious cross talk issues.

2. Do the same but the with the other line this time.

Cross talk is an issue, but remember that in the 100 pair cables going to an exchange you will have around 50% of the wires carrying DSL, and that is why BT use twisted pair cable.

Cross talk will generally only impact speeds significantly when using untwisted pairs. I would go on what the others in the thread said, not batboy in this case.