ADSL MAX Sync'ing

Hi,

I have just noticed that my modem is syncing at much higher rates than I
have been used to seeing here. I have heard that when ADSL Max is enabled
on your line, BT monitor it for a period of time and then set a maximum
speed by the results of the test. Is this correct? If this is correct,
does it monitor sync speeds at the start of each connection, or does it
monitor on-going (durng a connection).

I know I would never get 8mbit here, because of the line length, but at
present I am getting a sync of 4284. Which I assume is just over 4mbit.

When I just plug in the ADSL modem and nothing else on the line, this
increases to about 4900.

So what I am asking really is how long does it take BT to assess the line
quality and arrive at a figure to set the line speed at? Assuming that is
how it works. If thats not how it works, how does it work?

Thanks
Steve

Steve wrote:
> Hi,
>
> I have just noticed that my modem is syncing at much higher rates
> than I have been used to seeing here. I have heard that when ADSL
> Max is enabled on your line, BT monitor it for a period of time and
> then set a maximum speed by the results of the test. Is this
> correct? If this is correct, does it monitor sync speeds at the
> start of each connection, or does it monitor on-going (durng a
> connection).
>
> I know I would never get 8mbit here, because of the line length,
> but at present I am getting a sync of 4284. Which I assume is just
> over 4mbit.
>
> When I just plug in the ADSL modem and nothing else on the line,
> this increases to about 4900.
>
> So what I am asking really is how long does it take BT to assess
> the line quality and arrive at a figure to set the line speed at?
> Assuming that is how it works. If thats not how it works, how does
> it work?

It detects the highest, stable synch speed you receive.

On Fri, 2 Jun 2006, Steve wrote:

> So what I am asking really is how long does it take BT to assess the line
> quality and arrive at a figure to set the line speed at?

Read http://aaisp.net.uk/maxmagic.html for a digestible explanation.

Steve wrote:

> So what I am asking really is how long does it take BT to assess the line
> quality and arrive at a figure to set the line speed at? Assuming that is
> how it works. If thats not how it works, how does it work?

the modem negotiates the best speed it can to meet a target SNR margin
set by the exchange equipment (DSLAM). It does this every time it
connects, for ever. BT never set the line speed.

The data rate that BT fire at your line is set in 0.5M steps below the
sync speed of the modem, see link posted in this thread.

Phil

"PhilT" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) oups.com...
> Steve wrote:
>
> > So what I am asking really is how long does it take BT to assess the
line
> > quality and arrive at a figure to set the line speed at? Assuming that
is
> > how it works. If thats not how it works, how does it work?
>
> the modem negotiates the best speed it can to meet a target SNR margin
> set by the exchange equipment (DSLAM). It does this every time it
> connects, for ever. BT never set the line speed.
>
> The data rate that BT fire at your line is set in 0.5M steps below the
> sync speed of the modem, see link posted in this thread.
>
> Phil

The reason I asked Phil, is because I understand we have a line fault at the
moment which is keeping the speed below what (I believe) it should be
holding. I was worried that in the meantime, BT were monitoring my line for
a period of time and would set a poor speed at the exchange, which would
then not be allowed to be exceeded even after the fault was corrected.

So basically then, each time you connect it will try for the maximum
possible (presumably up to 8mbit)? Which means that however long my fault
takes to be sorted, it wont result in some figure being locked at the
exchange today or anytime in the future?

So you are saying that it will negotiate for the best speed possible,
forever?

Thanks
Steve

"Steve" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
>
I have a question for you Phil. By how much would you expect the line sync
speed to fall by adding a single BT phone to the line? (as opposed to not
having any telephone connected to the line)?

Steve

"PhilT" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) oups.com...
> Steve wrote:

> the modem negotiates the best speed it can to meet a target SNR margin
> set by the exchange equipment (DSLAM). It does this every time it
> connects, for ever. BT never set the line speed.
>
> The data rate that BT fire at your line is set in 0.5M steps below the
> sync speed of the modem, see link posted in this thread.
>
> Phil

So the stuff thats been said in here in the past few weeks/months is a
fallacy then? You are saying BT will never ever set a figure at the
exchange as a maximum possible conection speed?

So if your line has variable conditions, ie good sometimes, poor sometimes,
each log on will negotiate for the maximum possible speed (up to the 8mb)
each and every time you connect, forever? That right Phil?

Bri

On Sat, 3 Jun 2006, Steve wrote:

> The reason I asked Phil, is because I understand we have a line
> fault at the moment which is keeping the speed below what (I
> believe) it should be holding. I was worried that in the meantime,
> BT were monitoring my line for a period of time and would set a poor
> speed at the exchange,

AIUI, it could result in the *MSR* being set low, which would make it
more difficult in future to convince BTw that your line has
deteriorated. See MSR in http://www.aaisp.net.uk/maxmagic.html
and don't confuse the MSR with the BRAS.

> which would then not be allowed to be exceeded even after the fault
> was corrected.

No. When started-up on each occasion, the actual line speed will sync
at the highest (consistent with the required SNR margin, say 7dB) that
the line can instantaneously achieve. If line conditions deteriorate,
it will then drop, and re-synch at a lower rate.

These events are detected by BT, and lead to an adjustment of the BRAS
rate, which is one of the parameters which influence your achievable
IP throughput. See BRAS at the cited URL.

> So basically then, each time you connect it will try for the maximum
> possible

Indeed. If I switch mine on at a time when the line is quiet, it will
synch at an abnormally high rate (say, ~ 6.7M) which I know from
experience it will not be able to sustain. Then, as the line gets
noisier, it fails at that speed, and tries again, at say ~ 6.3M.
Later it'll fail again, and resync at about 6.0M, which is
sustainable, and then it'll stay up for days on end.

Currently it's showing 5952k, and has been up for nearly 120 hours.

As a Plusnet customer, I can see my BRAS rate - as reported by BTw to
Plusnet - at the mis-named URL
https://portal.plus.net/my.html?action=stable_rate , and it's
currently 5500. N.B that is *not* the MSR; see that A&A writeup to
understand the difference. I don't know what my MSR is (possibly
Plusnet do, I'm not sure?). But AFAIK the MSR is only used for fault
finding purposes, it doesn't affect your day to day operations.

The long and short is: if your line improves, then next time you
restart your box it will synch at a higher rate. Keep that up for a
few days, and the BRAS should rise to fit the new rate. Manual
restarts at least once a day in such a situation are said to speed up
the BRAS adaption, although I suppose the procedures are still being
tuned and refined as they get experience with this.

And in general I'd recommend reading the previous discussions, before
asking essentially the same questions all over again. It's not as if
this hasn't been extensively discussed in recent weeks, and those
helpful A&A URLs cited over and over.

"Alan J. Flavell" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed). gla.ac.uk...
> On Sat, 3 Jun 2006, Steve wrote:
>
> These events are detected by BT, and lead to an adjustment of the BRAS

And I thought Bras were for tits ! : )

Big Brian wrote:
> "PhilT" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed) oups.com...
>> Steve wrote:
>
>> the modem negotiates the best speed it can to meet a target SNR
>> margin set by the exchange equipment (DSLAM). It does this every
>> time it connects, for ever. BT never set the line speed.
>>
>> The data rate that BT fire at your line is set in 0.5M steps below
>> the sync speed of the modem, see link posted in this thread.
>>
>> Phil
>
> So the stuff thats been said in here in the past few weeks/months
> is a fallacy then? You are saying BT will never ever set a figure
> at the exchange as a maximum possible conection speed?
>
> So if your line has variable conditions, ie good sometimes, poor
> sometimes, each log on will negotiate for the maximum possible
> speed (up to the 8mb) each and every time you connect, forever?
> That right Phil?
>
> Bri

If the synch speed drops it will drop your speed in a matter of hours
& it would take 3 days of a better synch results to get it adjusted
upwards...