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NGB SAYS UPLOaD WILL BE 512KBS BUT CAN THIS BE SET AT LESS BY EIRCOM??
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11-08-2010 12:50pm#1
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Ok – I said I would do this so here goes.
To make for simple explanations – I have used some poetic license – so the techies out there will see some simplistic explanations of complicated items. By default this will mean that I have left bits out or explained in very simplistic terms…which is not always “technically correct”.
For the purposes of this entire explanation – I am going to use the analogy of a marble and a piece of card.
The marble is the data you want to send or get from/to (A to
the internet and the piece of card is your phone line.
The objective is to roll the marble from one side of the card to the other in a straight line – if you do this and can keep it going then you transfer data really quickly to and from the internet really well – if the marble falls off or does not go down the middle – then your success rate is lower or you fail completely. The more marbles you get through, the faster your throughput (speed).
There are loads of terms used in DSL so again I am going to focus on the ones that impact speed and the maximum speeds that a line can achieve.
Interleaving
In DSL there are 3 main settings for DSL (there can be more)
Low/off
Medium/normal
High/maximum
Interleaving takes big chunks of data and splits it into smaller chunks for transmission – this means that there is a higher chance that at least some of the chunks will arrive at the other side. The downside is that this increases the time taken for all chunks to arrive, as they arrive at different times and need to be reassembled. It also means that some chunks may not make it and need to be resent.
In DSL this extra time is known as latency. So the more interleaving that is done, the higher the latency. For gamers, this means higher ping times (a ping is really a measure of latency, usually in milliseconds)
Interleaving can be used to overcome a number of poor quality line problems and increases line stability at the expense of increasing latency.
Going back to our marble and cardboard. If we found that the cardboard we were using was bumpy or uneven (poor quality) – there is a higher chance that if we broke our marble up into smaller marbles that at least some would reach the far side. The ones that fell off can be resent later. This is much better than the marble constantly not reaching the other side.
Path/line length
This one is fairly simple and looking at the marble and cardboard scenario it is easy to say that if you are trying to roll a marble from A to B in a straight line, the longer the path, the greater the chance of failure. Certainly it would be hard to roll more than one marble at a time this means the marble throughput is probably going to be lower and slower than if the path was shorter.
This is exactly the same in DSL. The chances of data packets successfully reaching the other side is less and throughput is lower than if the line was shorter. This means longer lines have lower speeds and usually higher latency.
Attenuation
Attenuation is simply the loss of signal strength over a distance. The further is goes, the most signal that is lost. Naturally you could think that if you put more strength into sending the signal in the first place, that the signal would go further, however so would all the bad stuff associated with more power (more on this later)
Attenuation is usually expressed in dB (decibels) but this is just a unit of measure so don’t worry about it too much.
In our marble and cardboard world – Imagine you want to send the marble from A to B. you flick the marble and it starts moving but slows down over distance as it loses momentum until it reaches the other side. If the path is too long then the marble never reaches the other side (loop length too long = no DSL).
So why not flick the marble harder (more power). This will certainly work? Well yes, this is true it probably will but what if the cardboard is uneven or very long – the chances of the marble going from A to B in a straight line are very slim and in many cases it will hit a bump and fall off, or will become derailed as it travels.
SNR/crosstalk
Signal to noise ratio.
The signal to noise ratio is simply how much wanted signal (the good stuff) is there in comparison to how much unwanted signal (the bad stuff) in general.
“Noise” in communications is a bad thing and can come from many places both self created (too much power for example) or from an external source.
Imagine our cardboard and marble world. We are happily flicking marbles from A to B but some chap directly above us is also doing the same thing. Our cardboard is nice and even but the chap above has a bad bit of cardboard and is flicking very hard trying to get his marble to B.
His marbles are falling off and landing on our cardboard, sometimes causing our marble to go off track. This means we get less marbles through…as a result of the “noise” he is creating for us.
In the phone world – cables are packed closely together in bundles of pairs and have an impact on each other. Cross talk is how this manifests itself. The more cross talk, the less the quality of broadband.
Pre Qual
Pre-qualification uses several techniques to estimate the maximum speed that your line is capable of successfully supporting.
It is an estimate and not a guarantee.
The techniques usually used for this are known as SELT (Single ended loop testing) and DELT (Double ended loop testing)
SELT is usually used as it is a “one way” test that does not need end equipment to be installed in the customers location to do the test.
On short lines SELT tends to be reasonably accurate, up to about 90% but on longer line this can vary.
This is why pre-qual results do not always reflect maximum speeds or indeed why sometimes they are over or under estimated.
It is also important when the test is done – for example if the test is done during the night there are fewer people online, usually leading to less noise. This can overstate the result of maximum speed.
Telcos usually run the tests at scheduled intervals and limit the profiles available to the line to the maximum closest result achieved in the last test. This means pre qual results vary over time and can go up and down between testing intervals.
In our analogy, if would be like looking at our cardboard, considering how long it is, how smooth it is and how many marbles are dropping on it from other sources. We would then make an educated guess at our likely success rate for sending marbles from A to B (max speed). Depending when we look at the cardboard we may assume different results. Equally over time the cardboard may become rough (poorer quality) and we may revise our estimations.
Line profiles
Line profiles are a pre defined set of download and upload limits applied to each modem based on the maximum speeds that a line can support.
This ensures that the lines remain stable and indeed that the correct power levels etc are used.
In our cardboard analogy – this would be the maximum number of marbles we would be allowed to send from A to B over a time interval.
In DSL the time interval is usually “seconds” and the number of marbles is Mbps (Megabits per second)
Sync Rates
the sync rate is the rate that the DSLAM (the hardware in the exchange) and your modem agree on after having a wee chat. This is more accurate than the pre qual result as it is based on ACTUAL performance, rather than a guess.
when you power on your modem, it has a chat with the DSLAM, runs a few checks and then the modem applies the profile based on the one assigned by the service provider.
However, the profile is the maximum rate. If there happens to be a lot of noise on the line the actual rate agreed between the modem and the DSLAM may be lower than the profile applied.
Looking at cardboard and marbles - we made a guess at the maximum rate but once we started rolling marbles it could be that the cardboard was bumpier than we expected or indeed there could be more marbles dropping from other locations. In this instance, we reduce the number of mables we try to send than the previously agreed profile rate.
EVERYTHING above can impact the maximum speeds possible on DSL.
The “tricks” used to improve stability and speed do come at a price – for example high interleaving comes at the price of latency but line stability is improved. If we did not have these may people would not get DSL at all or would have terrible quality issues.
Pre qual is a bit of educated guess work and results do alter. No one deliberately lowers line speeds (why would they – usually means less revenue!!) it’s just a function of the automated result.0 -
All profiles that can be applied to the up to 8Mbps congestion free products in the attached.
If anyone wants a very long and boring account of lines and how they link to profiles etc - let me know
Hi Crawler ... just a slight update to your post
The 7Mb and 8Mb profiles on the Up to 8Mb are actually '7168/512' and '8192/512' ... hope this helps!0 -
Hi Crawler ... just a slight update to your post
The 7Mb and 8Mb profiles on the Up to 8Mb are actually '7168/512' and '8192/512' ... hope this helps!
Then the bitstream product description is incorrect....
See pages 11/12 of the eircom product description - is there sometihng we should know?
http://www.eircomwholesale.ie/dynamic/pdf/Bitstream%20Product%20Description%20V%2028.pdf0 -
Then the bitstream product description is incorrect....
See pages 11/12 of the eircom product description - is there sometihng we should know?
http://www.eircomwholesale.ie/dynamic/pdf/Bitstream%20Product%20Description%20V%2028.pdf
Ah ... didnt spot the 8192 profile at the top your pic the first time .. it's in there alright.... I stand corrected
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Ok – I said I would do this so here goes.
To make for simple explanations – I have used some poetic license – so the techies out there will see some simplistic explanations of complicated items. By default this will mean that I have left bits out or explained in very simplistic terms…which is not always “technically correct”.
For the purposes of this entire explanation – I am going to use the analogy of a marble and a piece of card.
The marble is the data you want to send or get from/to (A to the internet and the piece of card is your phone line.
The objective is to roll the marble from one side of the card to the other in a straight line – if you do this and can keep it going then you transfer data really quickly to and from the internet really well – if the marble falls off or does not go down the middle – then your success rate is lower or you fail completely. The more marbles you get through, the faster your throughput (speed).
There are loads of terms used in DSL so again I am going to focus on the ones that impact speed and the maximum speeds that a line can achieve.
Interleaving
In DSL there are 3 main settings for DSL (there can be more)
Low/off
Medium/normal
High/maximum
Interleaving takes big chunks of data and splits it into smaller chunks for transmission – this means that there is a higher chance that at least some of the chunks will arrive at the other side. The downside is that this increases the time taken for all chunks to arrive, as they arrive at different times and need to be reassembled. It also means that some chunks may not make it and need to be resent.
In DSL this extra time is known as latency. So the more interleaving that is done, the higher the latency. For gamers, this means higher ping times (a ping is really a measure of latency, usually in milliseconds)
Interleaving can be used to overcome a number of poor quality line problems and increases line stability at the expense of increasing latency.
Going back to our marble and cardboard. If we found that the cardboard we were using was bumpy or uneven (poor quality) – there is a higher chance that if we broke our marble up into smaller marbles that at least some would reach the far side. The ones that fell off can be resent later. This is much better than the marble constantly not reaching the other side.
Path/line length
This one is fairly simple and looking at the marble and cardboard scenario it is easy to say that if you are trying to roll a marble from A to B in a straight line, the longer the path, the greater the chance of failure. Certainly it would be hard to roll more than one marble at a time this means the marble throughput is probably going to be lower and slower than if the path was shorter.
This is exactly the same in DSL. The chances of data packets successfully reaching the other side is less and throughput is lower than if the line was shorter. This means longer lines have lower speeds and usually higher latency.
Attenuation
Attenuation is simply the loss of signal strength over a distance. The further is goes, the most signal that is lost. Naturally you could think that if you put more strength into sending the signal in the first place, that the signal would go further, however so would all the bad stuff associated with more power (more on this later)
Attenuation is usually expressed in dB (decibels) but this is just a unit of measure so don’t worry about it too much.
In our marble and cardboard world – Imagine you want to send the marble from A to B. you flick the marble and it starts moving but slows down over distance as it loses momentum until it reaches the other side. If the path is too long then the marble never reaches the other side (loop length too long = no DSL).
So why not flick the marble harder (more power). This will certainly work? Well yes, this is true it probably will but what if the cardboard is uneven or very long – the chances of the marble going from A to B in a straight line are very slim and in many cases it will hit a bump and fall off, or will become derailed as it travels.
SNR/crosstalk
Signal to noise ratio.
The signal to noise ratio is simply how much wanted signal (the good stuff) is there in comparison to how much unwanted signal (the bad stuff) in general.
“Noise” in communications is a bad thing and can come from many places both self created (too much power for example) or from an external source.
Imagine our cardboard and marble world. We are happily flicking marbles from A to B but some chap directly above us is also doing the same thing. Our cardboard is nice and even but the chap above has a bad bit of cardboard and is flicking very hard trying to get his marble to B.
His marbles are falling off and landing on our cardboard, sometimes causing our marble to go off track. This means we get less marbles through…as a result of the “noise” he is creating for us.
In the phone world – cables are packed closely together in bundles of pairs and have an impact on each other. Cross talk is how this manifests itself. The more cross talk, the less the quality of broadband.
Pre Qual
Pre-qualification uses several techniques to estimate the maximum speed that your line is capable of successfully supporting.
It is an estimate and not a guarantee.
The techniques usually used for this are known as SELT (Single ended loop testing) and DELT (Double ended loop testing)
SELT is usually used as it is a “one way” test that does not need end equipment to be installed in the customers location to do the test.
On short lines SELT tends to be reasonably accurate, up to about 90% but on longer line this can vary.
This is why pre-qual results do not always reflect maximum speeds or indeed why sometimes they are over or under estimated.
It is also important when the test is done – for example if the test is done during the night there are fewer people online, usually leading to less noise. This can overstate the result of maximum speed.
Telcos usually run the tests at scheduled intervals and limit the profiles available to the line to the maximum closest result achieved in the last test. This means pre qual results vary over time and can go up and down between testing intervals.
In our analogy, if would be like looking at our cardboard, considering how long it is, how smooth it is and how many marbles are dropping on it from other sources. We would then make an educated guess at our likely success rate for sending marbles from A to B (max speed). Depending when we look at the cardboard we may assume different results. Equally over time the cardboard may become rough (poorer quality) and we may revise our estimations.
Line profiles
Line profiles are a pre defined set of download and upload limits applied to each modem based on the maximum speeds that a line can support.
This ensures that the lines remain stable and indeed that the correct power levels etc are used.
In our cardboard analogy – this would be the maximum number of marbles we would be allowed to send from A to B over a time interval.
In DSL the time interval is usually “seconds” and the number of marbles is Mbps (Megabits per second)
Sync Rates
the sync rate is the rate that the DSLAM (the hardware in the exchange) and your modem agree on after having a wee chat. This is more accurate than the pre qual result as it is based on ACTUAL performance, rather than a guess.
when you power on your modem, it has a chat with the DSLAM, runs a few checks and then the modem applies the profile based on the one assigned by the service provider.
However, the profile is the maximum rate. If there happens to be a lot of noise on the line the actual rate agreed between the modem and the DSLAM may be lower than the profile applied.
Looking at cardboard and marbles - we made a guess at the maximum rate but once we started rolling marbles it could be that the cardboard was bumpier than we expected or indeed there could be more marbles dropping from other locations. In this instance, we reduce the number of mables we try to send than the previously agreed profile rate.
EVERYTHING above can impact the maximum speeds possible on DSL.
The “tricks” used to improve stability and speed do come at a price – for example high interleaving comes at the price of latency but line stability is improved. If we did not have these may people would not get DSL at all or would have terrible quality issues.
Pre qual is a bit of educated guess work and results do alter. No one deliberately lowers line speeds (why would they – usually means less :)revenue!!) it’s just a function of the automated result.
Excellent explanation!0 -
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Hi,
It's 7168/512. The doc will be ammended
And now it is ...
http://www.eircomwholesale.ie/regulatory/reg_details.asp?id=490 -
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