Digital transmission system hierarchy
PDH (Plesiochronous Digital Hierarchy)
SONET (North Am.)      SDH
STS-1           51.84 Mb/s
STS-3             155.52     STM-1
STS-12           622.08         STM-4
STS-48 2.488 Gb/s     STM-16
Japan
USA
Europe
J1  1.5 Mb/s T1  1.5 Mb/s     E1  2 Mb/s
J2  6  T2  6     E2  8
J3  32      T3  45     E3  34
J4  98      T4  274     E4  140