Connect: 10 Day Training Period Explained

[Lazarus]

This is a direct quote taken from: AAISP broadband internet: aaisp.net broadband

Wherever possible, I have removed references to the original ISP [...] so as not to cause confusion to sky customers.

Myth and magic of Max
There is a lot of confusion about Max services, and how it works. Even within BT there is confusion over the different aspects. People are confused as to what the 10 day period is when you first get Max, and what the BRAS cap is... Hopefully this page can clear up some of these issues.

Sync
Max uses fully rate adaptive ADSL. This means that your modem or router will sync at the best speed it can. However, it is not as simple as that! The modem measures the noise that it sees on the line, and works out what frequencies to use, and how much of each frequency. This ends up giving a specific speed. The fact that multiple frequencies are used over a wide frequency band is why it is called broadband in the first place.

The sync process has some parameters. The main one is the signal margin. This is how much room the modem gives itself to work correctly. In a perfect world one could say you don't need a margin, but in practice, the noise on your line can vary so a margin is needed. Some lines change over the day due to external interference, and so need more margin to allow continued operation throughout the day. Because each line is different, the correct margin is not something you can accurately predict. We'll see how the DLM is used to control this later.

Another aspect is interleaving. This is a technique that allows some of noise to be tolerated more easily. It is combined with forward error correction (FEC). An interleaved line cannot achieve quite the same level of max sync speed as a non interleaved line (presumably because of the overhead of the FEC). Interleaving does increase the latency on the line (the time for packets to be sent/received). There are different levels of interleaving and correction which can be used, but BT only use two settings, on and off. Non interleaved mode is called fast mode.

It is important to realise that these settings affect the way the router will sync, and do not directly affect the speed it syncs to. The same parameters will get a higher speed on a less noisy (or cleaner) line. The make of modem/router and the internal wiring can have an effect on the speed you get for a specific margin setting.

DLM: Dynamic Line Management
Because the parameters needed to get the most from a line depend on the line itself, they need a little fine tuning. BT have a range of ADSL profiles they can apply, as described above. These allow interleaving on or off, along with a margin of 3dB, 6dB, 9dB, 12dB, or 15dB of noise margin. The default is 6dB without interleaving

If the line syncs at a level where it is trying to work too fast for the line conditions, the modem will give up and re-sync (trying again). Every time the line syncs at a different rate BT notice. If the line syncs a lot then Bt will change the profile.

The process can be time consuming. One of the rules is number of re-syncs in an hour, with a very fast change in profile, but others are number of resyncs in a day, and a new profile applied the next day. It can take several days for the line to eventually settle at the right rate.

BT will normally apply interleaving if there are errors on the line, but [the ISP] can over-ride this, forcing interleaving on or off, or leaving it to BT. To change this takes [the ISP] one working day.

Eventually the line should reach a level where the margin is sufficient for a reliable service. This may mean the line syncs at a higher speed initially, but is unreliable, and after a few days it syncs at a lower rate and is stable.

Because the profile set is not a specific speed, but a margin, fixing any problems with internal wiring, or getting a better modem, can mean the modem syncs at a higher speed right away. BT say that they can also spot a line is good quality now, and adjust the profile back to a lower margin, but this takes many days and the exact algorithm is not clear.

BT are also planning to monitor the corrected errors when in interleave mode. The way this works is that errors can be detected and corrected, hence making the service work in the face of some interference. However this also provides stats of how many errors were corrected, and so allows BT to see the line is now clean and interleaving is no longer necessary. They plan to have a system to remove interleaving automatically in such cases.

Important: The DLM process is continuous. It is not just for the first 10 days, or some such - it applies to the line all the time. It is also important to realise that whilst we can control interleaving, we cannot set a specific DSLAM profile via BT.

BRAS rate
The DSLAM is the equipment at the other end of the phone line and with which the modem negotiates the sync/speed when it connects. However, further within BT's network is a BRAS (broadband remote access server). BT insist that they need to rate limit the traffic from the BRAS to the DSLAM. They have not said why, but they insist that the rate must be the same or lower than the sync rate of the line.

BT have an ongoing process to notice the rate the line syncs at and update the BRAS profile. The system should react to any decrease in sync speed within 75 minutes, and react to any increase in sync speed within 3 days. However, at present, it is generally reacting to any change within 15 minutes or so, up or down. Also the 3 day rule does not apply when a line is first converted to Max - it should have the new rate set within 75 minutes, before which it is set to a default 2Mb/s rate.

There are problems which BT are working on. Sometimes the rate is not set for days, or at all. However, for most customers, this process does work.
Why does [the ISP] need to know the rate? [The ISP] set a rate limit at [their] end to match the BRAS rate. This is not to stop you getting the full performance of the line. [The ISP] default it to the full 7.15Mb/s rate for a full speed line. [The rate can be used] to balance traffic when customers have multiple lines bonded. [It can also be used] to limit traffic in the event of a denial of service attack.

Important: The BRAS rate setting process is continuous. It does not just apply for the first 10 days.

MSR: Maximum Stable Rate
BT reckon that the DLM process will always achieve a stable line rate after 10 days. With ideal lines there are no adjustments, and with even quite bad lines the line is usually stable within a couple of days. In extreme cases it could take near to 10 days to finally become stable.

Once a new line is installed, or a regrade completed, BT wait 10 days for the DLM to stablise the line, and then take a note of the BRAS rate. They use this rate as a reference for speed related faults in the future. All this means is that if the line characteristics change and you no longer achieve the same sync speed on the line, BT will only consider it a fault if below around 30% below the MSR rate that was set after the initial 10 days. They are giving themselves some margin to allow for lines that just gradually change characteristics. Interestingly, they also limit the scope of the DLM adjustments if it would try and adjust a line such that it may sync below this fault threshold rate.

So, the 10 day period you may have heard of is just a reference used to set a fault threshold for speed related faults in future. The DLM and BRAS rate setting processes are continuous.

Sync capping
A new feature BT have now introduced is a temporary sync capping in the DSLAM profile. This is specifically where there are lines syncing hundreds of times a day. Basically - lines that never actually get a reliable sync and constantly keep trying.

Such lines generate a vast number of sync events which cause problems for the DLM systems. As such, when identified, a cap is put on the speed the line will sync. This then allows the line to sync reliably at this capped speed.

This is only done as a temporary measure. [The ISP should be] notified when this is done so that [they] can get whatever fault is causing the problem to be fixed. Typically this is some makes of router on particular line characteristics, and the solution may be sorting wiring, replacing splitters or even the router.

I thought this might also add some useful info to those who appear to be stuck on faulty bRAS profiles. It also may explain why routers are being sent out after connections become live.

Taken from a post on thinkbroadband.com :: MAX DSL - Tech Info

Copy of a post by JasonJ from Nildram

We have received an update from BT which explains an issue that is affecting some users' throughput for the first 3 days after DSL Max is installed.

Essentially when your DSL Max service first goes live, BT set a BRAS profile for the circuit. This should be done within 75 minutes, and should follow the line rate, but in some cases it is remaining at the old 2Mb rate. The circuit will still work, albeit at a maximum throughput rate of 2Mbps instead of the line rate.

BT is working to resolve this problem.

This will not affect every circuit, but we have no way of knowing which circuits will be affected in advance, and we will not be able to report throughput faults to BT on circuits that are affected.

A temporary fix has been put in place whereby subsequent synchronisation events will cause a reset of the BRAS profile within 75 minutes again. Unfortunately this fix will not work if you re-synchronise at the same or very similar rate to your first one.


What can our customers do to avoid being affected by this problem?

1). If your router/modem is NOT switched on when BT do the regrade then BT systems have time to register the change to Max, and you will be unaffected by this problem. BT carry out the majority of their regrades in the early hours of the morning, so leaving your router off overnight*, or better still whenever you are not using it, will increase your chances of the change to Max being registered and the first synchronisation event being picked up correctly.

*Please note - the date Nildram give you for your activation is a day after the confirmed BT date. We do this because we can't be certain exactly when in the 24 hour period BT will complete the install. Therefore, you would need to have your router turned off on at least the morning of the 10th if we give you an install date of 11th.


2) If your router is on when the regrade happens, and you feel that your throughput does not rise (after 75 minutes) to be loosely in line with your sync rate, run a speed test either here at thinkbroadband :: The UK's largest independent Broadband / ADSL review site - Your guide to UK broadband Internet. or over on www.kbps.co.uk - Speed Test Home .

If you are still seeing throughput in line with your pre-max speed, turn your router off, and leave it off for a period of at least 30 minutes, before turning back on to re-sync. You may then get picked up by BT's temporary fix and things will right themselves in 75 minutes, but not if your router re-syncs at the same or similar rate. In that event, your profile will be stuck for 3 days, and we will not be able to progress a speed related fault on the circuit until after this time.

I hope this goes to dispel a few myths that have been floating around about the 10 day training period.

[Jockdownsouth]

Does this mean that the router should be left switched on for the first 10 days, rather than switched off with the PC? What happens if you're away for part of the time? Sorry if these are "idiot" questions!

[NewsreadeR]

Hi

If you are on Mid, this does not apply, only to people who are on Connect.