what's channellized E1?

Yes, an E1 has 32 * 64k timeslots, one is reserved for timing (thus
leaving 31 real channels), and if your running ISDN on it, one gets
reserved for signalling (ts16)

(Or you can run an E1 in untimed mode and get a point to point 2048k circuit)

Many Euro telcos will provide a bunch of various size circuits adding
up to 31*64k delivered as an E1 at the ISP , the router then is told
which leased line is on which timeslots, and they then look like a bunch
of seperate interfaces. Very good for port density !