T1
http://en.wikipedia.org/wiki/Network_interface_device
Extending out from Demarc
Well, first off, T1/DS1 is not spec over Catagory <anything> cable. it's fine for shorter runs, but will fail with any real distance, even within the usual structured cabling limitations.
What you need is "Premises Cable" which is individually shielded pair inside a shielded jacket.
If you go to www.anixter.com and do a catalog search on premises cable, yyou'll get a list.
It is available in two pair, or more.
With Prem cable, you can run up to 655 feet from the demarc and still be in spec for T1/DS1.
Beyond that, you should probably get the demarc moved.
(what's the difference between moving the demarc and extending the demarc. you ask?
Well, the signaling to the smartjack / niu is (usually) HDSL; once it passes the smartjack / niu, it's standard DS1/T1 signaling .... HDSL can handle the extra distance, DS1/T1 cannot (beyond 655 feet).)