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How DSL Max works

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Maximum Speeds

Although MaxDSL is advertised as "Up to 8Mb", in reality even if you have an excellent line and manage to sync at the full 8128 kbps, the very maximum throughput speed you can receive will be nearer 7Mb due to ATM and other overheads.
It is also anticipated that speed variations will be much greater particularly during peak periods due to factors such as exchange congestion etc. In fact BTw even warn that at peak times speeds may be the similar to an equivalent 2Mb fixed rate service.

More information about the actual dslMax products themselves can be found on my maxDSL page.

maxdsl diagram Rate Adaptive Managent Box Dynamic Line Management Network Configuration & Assignment System bRAS Rate Adaptive Profile Internet ISP Home Gateway / LTS cluster ISP Central Pipes Internet Colossus IP Network ATM Cloud DSLAM adsl modem router ATM backhaul Log in Event Collector Data Collector Central Plus ISPs only

bRAS Broadband Remote Access Server   DLM Dynamic Line Management
DSLAM Digital Subscriber Line Access Multiplexer   NCAS

Network Configuration & Assignment System

RAMBO Rate Adaptive Management Box   RAP Rate Adaptive Profile

Sync Speed

Sync speed is the rate which you connect (synchronise) to the local exchange at. This speed is negotiated between your router and the DSLAM at the exchange and will be subject to line conditions such as your SNR Margin and line length.

With maxDSL it is quite possible that your sync speed may vary each time you connect. - It is not unusual to get better sync speeds during the early hours of the day/night than in the evening.
Various factors can cause more noise on the line in the evening, which may result in a lower sync speed.

When an End User logs on with maxdsl an "Event" will be sent to the DSLAM. Your modem/router will negotiate with the DSLAM what speed your line can achieve. Details of these events are monitored by the DLM. Some users may notice a slight increase in the time it takes to sync to the exchange due to this negotiation process.

To give your line the best chance at attaining higher and more stable speeds it is recommended that you follow the tips on my low SNR page.

Maximum Stable Rate. (MSR) - Training / Stabilisation Period.

During the first 10 days on MAX details of your logon/sync events are recorded in an Event Collector which every 15 minutes then sends this information to RAMBO.

RAMBO collates events from all users and analyses each users data over a 10 day period to find the Maximum Stable Rate (MSR) for their particular line. The MSR is set from the lowest achieved rate over this 10 day period rounded down to the nearest 0.5Mb. A notification after this period is sent to the RAP profile and your ISP.

During your first ever log in to maxdsl, information is sent from RAMBO over to RAP which forwards the details over to the DSLAM at the exchange in order to set your sync speed.

Sync speeds (and Data Rates) for poorer lines can and will vary over the this training period and users may experience frequent disconnects and slower speeds until their most stable rate is found.

The 10 day training period is often referred to as the "Stabilisation Period", and will only commence once a line has been in sync for 15 mins or more - not necessarily the date from when the line is maxed. There is a rolling 10 day period which allows flexibility if for some reason sync is not attained during the immediate period after the line being maxed (such as holidays and the router is switched off).

There's been a lot of talk/hype about the MSR, but in day to day use it doesn't really do much as its main purpose is to set your Fault Threshold Rate.
Your MSR will generally stay the same throughout MAXdsl, although a BTw engineer can request the MSR process can be restarted. There has also been some rumours that the MSR process can be restarted during migration but this is not the case. particularly in the when of migrating between 2 IPStream ISPs.

With Datastream products, BTw will collate the relevant information but not send it over to the bRAS since this equipment is owned by the DS provider. Instead the information is sent in a report to the DS ISPs so that they can apply the speed to their own bRAS. Once the 10 days have passed BT will also advise the DS provider the stable rate.

Fault Threshold Rate.

Once your MSR has been set, BTw use this figure to calculate your Fault Threshold Rate which is in the region of 70% of your MSR. BTw will only investigate speed related faults if your speed drops to below the Fault Threshold Level.

Data Rate
(bRAS profile)

The Data Rate is the fastest speed (throughput) that you will be able to download at and is profiled by BT at the bRAS.
A maximum throughput level is needed to stop more data than your line can physically achieve being sent down the backhaul and being dropped at the DSLAM.

For more information see bRAS / IP profile page.

The Data Rate should not be confused with the MSR.
Some ISPs allow you to check your Data Rate. PlusNet customers can view their Data Rate here.

Stuck bRAS profile.

Many customers have found themselves with the dreaded "Stuck bRAS profile". This is when despite constantly syncing at much higher speeds, your IP profile remains stuck at 1mb/2Mb. For some reason the DLM system hasn't picked up that you have been upgraded from your traditional adsl speed to your new sync speed.
Personal observations tend to show that it is generally the better lines which tend to get stuck on their old 2Mb speed, possibly because their SNR is better and they suffer from fewer fluctuations.
If your newly maxed connection constantly syncs at high speeds for more than 3 days, and you cant get speeds over 2Mb, check your IP profile on the BT Performance test. If this figure shows as 2000 for more than 3 days, then the likelyhood is that you have a stuck bRAS profile. In this case you need to contact your ISP to ask BTw to reset your IP profile.

SNR /SNR Margin

The Signal to Noise Ratio on the max product is more flexible than on traditional adsl. On the older fixed line speed products an SNR Margin of less than 6dB suggested that there was a problem with the line.

With Max a target SNR margin is set on the DSLAM and its your router and the DSLAM that agree the best way of meeting this target margin. The target margin range is between 3dB and 15dB and rises in 3dB increments - although it is normal for it to fluctuate either side during the training period. The default is 6dB without interleaving.

Dynamic Line Management (DLM) - Ongoing Process

When the user logs on they send information (line data) to the DSLAM including details of any errors on the line.
The information is collated by the Data Collector which in turn sends it to the Dynamic Line Management system. Its the job of the DLM to analyse the data from the DSLAM and RAMBO to then decide if there is a stable line. If not if any changes to the SNR should be made and/or Interleaving should be used. The constant management ensures that the circuit remains within the set threshold.

If any changes need to be made the DLM sends the information via the flow stream to NCAS.
NCAS then reports to the DSLAM which then makes the relevant changes to the individual users line card. This process will be repeated to ensure the correct changes have been made.
If necessary this process will be continually repeated changing the SNR and/or interleaving until the line is deemed stable.

The DLM process is carried out every time you are connected and not just within the first 10 days.
Configurable attributes of the DLM are SNR and Interleaving.

© April 2006
IP and bRAS profile speciific information added Oct 2007

MaxDSL products and how it differs from traditional adsl.
My personal maxdsl experience.


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