Does a re-synch always result in a lower IP Profile?

I still have not had any real answer on this.

DLM always seems to lower a IP profile. Can anyone explain how a higher synch is achieved ? (Without any user intervention, after recent experience I want to leave the modem & router on)

The IP profile reflects the synch speed, DLM influences the synch speed. Speeds can increase if the error rate reduces etc but this will take longer to recover than it took to drop in the first place as the systems are biased towards stability.

Your modem can only get to a higher speed by resynching under an external influence, whereas it will fall to a lower speed automatically if it can't hang onto the speed it is connected at.

In reply to a post by shalom2005:

DLM always seems to lower a IP profile. Can anyone explain how a higher synch is achieved ? (Without any user intervention, after recent experience I want to leave the modem & router on)

You've answered your own question- without user intervention, you have to wait for the DLM to do its own thing.

IME experience, if something causes a drop in sync and then goes away the DLM will eventually force a re-sync to a higher speed, but it takes its time about it- it's not impulsive, even if the noise is .

Still unclear!

"Your modem can only get to a higher speed by resynching under an external influence"

Can you please explain what 'an external influence' is?

(I'm happy to leave my modem & router connected now as I recently had a drop from 66-59Mbps. I'm unclear how a re-synch can occur if my connection is 'always on'. My line is very stable & can stay that way for 28 days or more.)

Thanks for your patience with my questions!

an external influence would be either you turning it off and on or asking it to resync via a user interface, or the cabinet DSLAM dropping the connection to force a resynch perhaps in repsonse to DLM changing parameters.

In other words your modem will not automatically seek a higher speed on its own account.

Ah thanks Billford. You typed at the same time as me

That's clearer. So, if DLM sees a really stable line, it will eventually resynch to the maximum the stable line can take. I just have to wait for it to do so.


Thanks guys.

Thanks Yarwell. So, the modem may not force a resynch, but the cab DSLAM will hopefully force a resynch in the future. Good that's what I was hoping.

Many thanks

In reply to a post by shalom2005:

I just have to wait for it to do so.

Yup, and be prepared for (potentially) quite a long wait, it can take weeks.

I'm not sure if anyone really knows how the DLM comes to its decisions (and I'd include OpenReach in that!), but it seems to depend on how large it thinks the improvement would be. If it's substantial then it can be fairly quick (days) but if it's only slight then it will take a lot longer.

Summary. While waiting for a DLM speed increase, reconnect the router each morning.

The IP profile reflects the synch speed, DLM influences the synch speed.

The sync speed is effectively controlled by DLM as part of the low level cabinet->modem connection. The IP/BRAS profile is established from the sync speed as others have said above.
However, this does not happen completely automatically, it only happens when the router establishes a new pppoe connection.

A change of sync speed always involves a new connection from cabinet->modem. Sometimes, as the connection is broken at the lower cabinet->modem level, the pppoe connection is lost at the higher (router->exchange) level. Once the lower level connection is reestablished at the new sync speed, the router makes a new pppoe connection and a new IP/BRAS profile is correctly established.

However, quite often the reconnection at the lower level happens so quickly that the higher level connection does not notice the drop. The pppoe connection is not broken and does not need to be reestablished, and the IP/BRAS profile remains at its previous level, matching the old sync speed. This can be resolved by manually disconnecting and reconnecting the router (not modem); preferably using the web interface, or alternatively by resetting or power cycling the router.

When hoping for a rise in speed, it is worth reconnecting the router each morning; DLM usually schedules sync speed increases overnight. The speed you see is effectively the lower of the sync speed and IP/BRAS profile. Where the new sync speed is faster than the old, you will be left with a lower IP profile which will artificially keep your speed down. Where the new sync speed is slower than the old, it will be the sync speed that limits you. Reconnection will lower the IP profile, but won't lower the speed you actually see.

There is never any harm disconnecting/reconnecting the router. The router reconnection is not seen by DLM; unlike power cycling the modem which can be seen as an error by DLM. As FTTC connections are often very stable for months at a time, you could suffer unnecessarily low IP profile and speeds for such periods after a DLM increase if you do not reconnect at the router level.

As also mentioned above, the DLM rise in speed can take two to three weeks; DLM is very keen on making sure of stability.

Edited by StephenTodd (Tue 12-Feb-13 09:48:17)

In reply to a post by StephenTodd:

The speed you see is effectively the lower of the sync speed and IP/BRAS profile. Where the new sync speed is faster than the old, you will be left with a lower IP profile which will artificially keep your speed down.

Not on a fibre connection- the IP profile is a fixed percentage of the sync speed (I forget the value- 96 point odd?) and takes effect immediately.

FTTC uses OpenReach's DLM, not BT Wholesale's, and it's a lot more end-user friendly.