synchronous transport signal (STS)
Synchronous Transport Signal (STS) are hierarchy levels of Synchronous Optical Network( SONET) based on transmission rate of OC-1 with 51,840 Mbit/s.
Common values for the synchronous channel signal are 1, 3, 6, 9, 12, 18, 24, 36 and 48 for n (STS-1, STS-3 to 48, corresponding to OC-1 to OC-48) resulting in speeds of 51,84 Mbit/s (STS-1), 155.52 Mbit/s (STS-3), 466.560 Mbit/s (STS-9), 622.08 Mbit/s (STS-12), 933.120 Mbit/s (STS-18), 1.244160 Gbit/s (STS-24), 1.866240 Gbit/s (STS-36), and 2.488.32 Mbit/s (STS-48). Also referred to as Optical Carrier (OC-1 to OC-48), where STS specifies one frame, unlike OC.
There are also transmission speeds of 26.920 Mbit/s (STS-1/2) and 12.000 Mbit/s (STS-1/4).