SDH

Synchronous Digital Hierarchy, the European counterpart to SONET.

Here's a little crib sheet with the more usual link capacities (E1 to OC ratios are comparable):

OC3     100xT1 STM-1   155Mbps
OC12    401xT1 STM-4   622Mbps
OC48   1606xT1 STM-16  2.5Gbps
OC192  6424xT1 STM-64   10Gbps
OC768 25699xT1 STM-256  40Gbps

T1=24x64Kbps
E1=30x64Kbps
E3=480x64Kbps