T1 is an old style dedicated leased cable line connection.
Its ~1.5Mbit synchronus (same up as down).
It is also 1:1 contention and comes with guarantied uptimes and stuff usually.
Costs an arm and both legs. and has very limited avaliability in this country. Especially since its been replaced by T3 (3x the speed) but again thats rediculous pricing for anything but medium -> large businesses.
Personally my halls connection last year was excellent but that aint gonna happen retail. I'd like high speed sdsl but cost is the main thing. We've just downgraded to 1mbit adsl from 2mbit because it was just two expensive between the 3 of us (there was 4 before)
K
Edit - this site gives lots and lots about the original t1 standard, needless to say its 1.544mbit,
http://www.dcbnet.com/notes/9611t1.html
Oh btw i'd really like an oc connection, oc3 would do, oc48 would be nice and oc192 i wouldnt know what to do with it.
Most OC connections are limited to isp's and internet backbone stuff. It would be cheaper for move to central london than the installation charge by far !