VDSL2 broadband provider switch - A few questions

I've NEVER switched broadband providers before - I had always been a Virgin customer until I moved to a building that had 100/100 FTTP included in the rent - When I moved from there I signed up for VDSL2 with TalkTalk. Since I've had a string of issues with their customer service I am going to "JumpJump" ship to another provider!

1) Does anyone know how long broadband is down for whilst switching to a new provider? The letter states "upto" 24 hours but when I ordered I was told by the person on the phone it would be down 30 minutes and an hour at the very most

2) Do I get any sort of warning? - Like will I get a message from my new provider saying "We will start the switch in 10 minutes, if you are doing anything important online, wrap it up now" or will the only warning I get be "No Network Connection"

3) Will I have to go through the DSLAM process again of it starting me off slow? When I joined TT I started out with about 50Mb and I was madly interleaved (40ms+ ping) - Will DSLAM remember my current profile? My router currently syncs at 80/20

Downtime depends on when the gaining/new ISP enable their part mainly.

OpenReach will flick a switch (Not literally, it's just a routing change) which will change your current DSLAM port routing from Talktalk to the new ISP.

At this point you need to change the ISP supplied hardware at your end or configure your router for the new ISP.

There will be a loss of sync, usually with a DLM reset.

If the new ISP has their end setup then the swap will be under an hour.
Some ISP's don't have their end enabled till later in the day.

No warning is given.

The DLM resets to Interleaving in most cases, adding 8ms latency and lowering the sync speed.

If you're on a Huawei cabinet this added latency should disappear after a few days as G.INP is enabled.

Edited by j0hn83 (Sun 06-Oct-19 17:38:18)

As has been suggested it can depend on which ISP you are moving to. We might be able to be more specific if you tell us which it is.

Some seem to have your account active from the start of the changeover day so if you have left your modem/router set up it just "happens". At least one waits to get a notification from Openreach that the switch has been made, but they only ask Openreach for the latest list now and then. Which is where the hour or so can come from.