E1 that my sources of information all seem to concur on is that E1 can provide up to 2.048Mbps.
E1 has 32 time slots if all of them are used to carry data or voice then it makes since 32 TS x 64 kbps = 2.048 Mbps
But of course TS0 is reserved not to carry data or voice as TS0 is allocated entirely to frame alignment signal pattern, a remote alarm indication bit,,,,,etc.
TS16 reserved for CAS/CCS signalling in a voice environment, not in a data environment
Means we will end up 30 B channels of bandwidth for voice and 31 B channels for data ,,,,,,,,right ?
(Voice environment) TS0 and TS16 not to be used means we end up with 30 B channels x 64 kbps = can only achieve 1920 kbps. Say we add the 64 kbps D channel to that then still we miss our target and we only achieve 1984 kbps.
(Data environment) TS0 not to be used means we end up with 31 B channels x 64 = can only achieve 1984 kbps.