high attenuation

Hi all, I currently pay �35 for my Broadband service to a terrific company - excellent customer service, fast speeds if line allows. . But unfortunately my line quality does not merit me paying such a premium. I am about 6km from my exchange, and its old aluminium cable laid from exchange to cabinet so I am stuffed.

I used to sync at 1.5MBps or so and I settled for that but my line degraded to around a 1.0Mbps sync ( they are building loads of new houses all around me and I wonder if somehow the line has "lengthened". Even that 1,0Mbps sync occasionally ( every couple of weeks or so ) collapses to 250kbps or so and takes a couple of days to recover.

BT have sent engineers out twice but are no longer playing ball..they insist the line is ok, its simply distance from the exchange and are now even claiming that my line can't sustain BB Max at all and I should go back to 512 fixed.

Given I can't justify �35 a month for such a slow speed, I am thinking about Sky ( �5 for Mid ) . What happens if my line won't even sustain that , will Sky allow me to end my 12 month contract ? Do they even offer a 512 fixed service if I have to revert to that , if so what download limit ( looking for 40Gb ) ? Can someone advise with my line attenuation of 63.5dB what speed I may expect on Sky LLU Sorry, so many questions :-)

Bandwidth (Up/Down) [kbps/kbps]: 448 / 1,056
Data Transferred (Sent/Received) [MB/MB]: 14.73 / 280.73
Output Power (Up/Down) [dBm]: 12.0 / 15.0
Line Attenuation (Up/Down) [dB]: 31.5 / 63.5
SN Margin (Up/Down) [dB]: 14.0 / 12.0
Loss of Framing (Local/Remote): 0 / 0
Loss of Signal (Local/Remote): 0 / 0
Loss of Power (Local/Remote): 0 / 0

Looking at those line stats, I would suggest a half meg fixed rate connection be your only sensible option. Anything rate adaptive, as you rightly suggest, is going to flap like a pig and it would appear you have a choice of stable and slow or flakey and possibly slightly faster (assuming your BRAS profile doesn't get shoved down to 160k for a flakey line).

If you have many new properties being built, it is likely cross-talk from their (presumably shorter) lines would be the cause of your loss of margin, not that your line has lengthened, although it is possible I guess.

My experience has been that Sky has given better results on my line than any other provider. Don't forget that you have a 10 day period in which you can cancel and be no worse off. With Sky LLU you don't have line profiles, so if your line is continually up and down, you get the best of what's currently on offer.

Hi,
I've had problems with my line since moving to my current house 3 months ago. I live quite a distance from the exchange, and my speeds fluctuated between 2 and 3mbit for the first month.

Then Sky DLM'd me, and for 3 weeks I had a speed between 180k and 384k! After that finished, I rang up support and got the speed upped. After several calls to try different values, seems I am settled on 1440k.

Not quite the same as the 20mbit I used to have on Virgin, but is sustainable - tried downloading large files and watching the speed during transfer - constant 1.4Mbit.

My stats are
Attenuation: 60 / 31.5
Noise Margin: 15.8 / 13

Sky Support are very helpful, and will do what they can to help improve things. However I believe the first 10 days is when your line is on some stability testing (someone else here may be able to clarify / coorect this), so not sure if they will alter your connection speed during that time.

Not exactly an yes or no answer, but might help you make a decision.

Ok basically if you move on to the sky mid package if it is available in your area to check this go to www.samknows.com and go to availibility tracker and put in your phone number and it will tell you all the providers that are available in your area.

layout of sky packages:

sky connect:
(up to 8mbps can be fixed to 512kbps if needed and a 40 gig download cap a month. This package will cost �17 pound per month if sky equipment is not in the exchange but if sky equipment is in the exchange but full it will cost �5 per month)

There is no sky llu equipment in your exchange so you will have be connected to bt equipment and they will manage the connection and you will have a bras profile and a 10 day training period were the speeds will vary.

sky base:
(up to 2mbps can also be fixed to 512kbps if needed and a 2 gig download cap a month. This package is free if you have sky tv and you can also get free sky talk)

There is sky llu equipment in the exchange so you will be connected to sky equipment and sky will manage it and there is no bras profile or training period.

sky mid:
(up to 8mbps can also be fixed at 512kbps if needed and a 40 gig download cap a month. This package is �5 per month)

There is sky llu equipment in the exchange so you will be connected to sky equipment and sky will manage it and there is no bras profile or training period.

sky max:
(up to 16mbps can also be fixed at 512kbps if needed and unlimited download. This package is �10 per month)

There is sky llu equipment in the exchange so you will be connected to sky equipment and sky will manage it and there is no bras profile or training period.

I hope that helped you with the questions that you were asking.

Thanks all for the replies. I checked Samknows and Sky LLU is indeed available on my exchange. Given I now know I have the fall back of 512 fixed if I find ADSL max unusable then I will move to Sky mid at �5 per month. This gives me the download useage I require. I currently pay �35 p/m for this on fast.co.uk.

Given my high line attenuation , 63.5 db, aluminium line and distance from the exchange, I currently get a ( mildly flakey 750kbps down, on a sync speed of 1056 or thereabouts -sync collapses every couple of weeks but recovers in a day or two ).

Do you think I would get faster with Sky LLU given no BRAS ?

yeh i think you would be better on skys llu package it is cheaper,the line can be readjusted if it needs to be there and then none of this regrade [censored] and also the throughput would be better as what you sync at is what you get unlike the bras profile were the sync speed is different from the throughput.

Since there's no line profiles on Sky (BRAS), you get what you're currently sync'd at, so if you have a line with varying line noise, and you don't mind restarting your router occasionally, you could benefit.

So there is not ATM overhead on the Sky LLU service too?

Sky use interleaving and they can also reduce your max delays which would make the whole process quicker again.

And back to the question, does the IP throughput match the sync speed, or does 10% to 13% still need to be allowed for due to the overheads of IP carried over ATM?

I know what interleaving is, but when you say 'reduce your max delays' what do you mean?

Methinks Jonny is proving the old proverb "A little knowledge is a dangerous thing"

Of course, when I said that on Sky "you get what you sync at", I didn't mention overheads, because these are inherent in any system.

Edited by deleted (Sun 27-Jul-08 10:35:29)

FYi on sky BB 8mb LLU Mid - i sync at 8188 and dl at 860-900 kb/s around 7.2-7.6 mb

Sky cover these overheads by giving there users a bit of extra speed so they are not losing out on anything they are getting what they pay for so what exactly is your point.
And another thing when i said sky can lower your max delays what this basically does is improves latency so there is really no need for the extra sync speed if you have got very low ping times.
lower ping times=faster browsing,online gaming,etc,etc

Edited by jonny1310 (Tue 29-Jul-08 04:45:10)

Okay so what you are saying is that Sky can control the depth of interleaving on its LLU products.

As for Sky giving extra speed, you are still losing me. I think what you mean is something like this.
If a line is sold as 2Mbps, it will sync at 2272Kbps (which BT Wholesale do too btw).

Otherwise on the rate adaptive lines if it syncs at 10Mbps, then max IP throughput will be around 9Mbps.

Assuming gaming traffic is low, e.g. 128kbps or less, then sync speed makes no difference, so the comment about no need for extra sync speed is hogwash in terms of lowering latency.

if I a line synchs at 4530kbit on sky you will get that speed, on a ipstream isp you will lose 530kbit as you on a 4000kbit ip profile, I assume this is what he meant by extra speed.

So Sky is not using ATM for the ADSL link, but IP then? So now 10% overhead due to the 48 bytes of IP payload in each 53 byte ATM cell.

On IPStream 10-13% of 4530Kbps is around 453Kbps - you need a sync of 4544 to get the 4Meg profile.

So I still don't really know if Sky are managing to get around the ATM overheads. Given its a fairly standard Netgear router I don't believe they are.

4530kbit on ipstream = 4000kbit - atm overheads - tcp overheads.
4530kbit on sky llu = 4530kbit - atm overheads - tcp overheads.

the atm overheads are still there but the IP profile overheads are not.

Indeed BRAS profiles are not a cure for ATM overheads, simply a way of vastly reducing the bandwith they might otherwise need if taken over the 5 million or so subscribers on MAX (if I was being cynical)

Both IPStream Max and Sky's LLU implementation suffer slightly from ATM overheads, the difference is BT also add a rather unnecessary 'penalty' with their BRAS profile implementation.

The bottom line is I download a lot quicker with the same ATM sync speed on Sky than I did with BT, and it's not down to congestion at the exchange or ISP, it's simply down to the profiles implemented by BT.

I'm not sure what Andrew is finding difficult to understand here?

On IPStream .....you need a sync of 4544 to get the 4Meg profile

True, but when have you ever known the actual usable data (that which is available as pure downloaded data for programs, browsing, download managers, etc.) on a 4Mbps IP profile (on IPstream) to actually be 4Mbps?
3.7Mbps might be a closer value.

I think what these people are saying, is not that with LLU (Sky, BE, etc.) you get more bang for your bucks, it's just your "bucks" don't need to increase by 0.5Mbps to get more "bang" (oh wait, then you do get more bang for your bucks ).
I'm pretty sure the Sky LLU throughput (that which is coming out of a download manager, for example, rather than that which is going back & forth between the router & DSLAM) for a 4544kbps sync will be pretty close to the 3.7Mbps you'd get from IPstream.
Sky (and the other LLU companies) are faster for most, because not too many people sync at smack on the IP profile threshold, so they get a higher speed than they'd be getting from IPstream.
That's, of course, not even taking into account the 5 day stupidity (if your sync goes up, on Sky/BE/etc., you don't have to hope if holds up for five days before getting an increase in throughput).

So, except in a few cases (where people sync exactly at a particular IP profile threshold level), LLU is faster than a BTw IPstream product, and LLU will also be faster (up to 1Mbps faster) than a BT WBC ADSL2+ product).

Edited by adebov (Fri 01-Aug-08 22:08:34)

Hmmm, isn't interleaving bad for on line gamers ? Good for batch downloads but not for sessions with lots of interactions surely ?

Yes it is but getting max_delay turned down from 32ms to 8ms means that your added time overheads are minimised my pings are higher than when I was with Bulldog and Pipex but certainly not to the point of unplayable. Currently the servers I play on, both in Germany, I get a very steady 45-50ms.

Interesting, thanks

To do it correctly:

4530kbit on ipstream = 4000kbit - tcp overheads and computer setup etc
4530kbit on sky llu = 4530kbit - atm overheads - tcp overheads and computer setup etc

The ATM overheads are catered for in the IP Profile setting, it would be an ATM profile if it did not

I am well aware that LLU will waste less of the sync speed due to no IP Profile, but am trying to make sure people not are fooled into thinking that on LLU their sync speed should be their maximum IP throughput.

I was actually wrong in my initial post.

If we use your algorithm it would actually be this. Since 4544 gives the 4000 I made a mistake.

4530kbit on ipstream = 3500kbit - tcp overheads and computer setup etc
4530kbit on sky llu = 4530kbit - atm overheads - tcp overheads and computer setup etc

4530kbit on ipstream = 3500kbit - tcp overheads and computer setup etc

So, as near as makes no difference, 3.2Mbps.

4530kbit on sky llu = 4530kbit - atm overheads - tcp overheads and computer setup etc

So 3.7Mbps (around 32kbps less than an IPstream connection syncing at 4544kbps).


In this extreme example, LLU will be almost 0.5Mbps faster than an IPstream product with the same line speed.

Take it one step further (into the not to distant future of ADSL2+ WBC - provided by BTw), and an LLU connection could have a usable data throughput almost 1Mbps faster than available from a BT WBC product with the same line speed!

Whatever happens, if the background infrastructure is there to support it, an LLU connection will never have a maximum throughput lower than a BTw product, and will have a maximum throughput up to 0.5Mbps (1Mbps for WBC/ADSL2+) faster than a BTw product (for the same line speed), but the extra speed has little to do with overheads (IP or ATM) and everything to do with BT's profiling system.

and the example assumes the profile isnt stuck

it may be stuck lower eg. 1mbit

Edited by Chrysalis (Wed 06-Aug-08 03:21:43)