I've had this problem for a year or two now, was hoping moving from the Exchange to a cabinet, or changing routers would solve this - but nothing I've done has been able to fix it so help!
Basically I get a ADSL2 line sync quickly, then with both a Vigor2710 and Netgear DG834G router I get a long wait (around 3 minutes to 15 minutes) for a PPP tunnel to go up.
The netgear shows this as a LCP link failed to come up.
The Vigor shows a bit more details and always lists 1 RX CRC Packet error on the ADSL connection before the PPP comes up.
Interestingly enough once the PPP has connected, at least with the Vigor2710, I can bring the PPP down and back up and it's nearly instant.
I'll log a ticket with Slingshot, but hoping someone would have any ideas.