G.704
G.704 is the framing specification for G.703. A carrier can 'steal' a 64kbps time slot (TS0) from a 2.048 Mbps line and use this to provide timing. The result is that 31 time slots are left for data, which equals in a bandwidth of 1.984 Mbps.
Normally G.703 lines with G.704 framing is called Structured G.703. Carriers offer G.704 when their network is built up on a cross-connect basis, and will offer unstructured G.703 when their infrastructure is based upon multiplexers.