What a STM-0 contains

A STM-0 carries 672 DS0s, per ITU-T G.707 and ANSI T1.107.

STM-0 → 28 × DS1 → 24 × DS0

E1 mapping: 21 E1s, which is 630 voice channels at 30 per E1. E1s in a STM-0.

Down to DS0

28 × DS1 ITU-T G.707One VC-3 holds 7 TUG-2 × 4 TU-11 (DS1).
1. 24 × DS0 ANSI T1.10724 payload timeslots. The framing bit adds 8 kbit/s and brings the line rate to 1.544 Mbit/s.
1 × E3 ITU-T G.707Client mappingOne TU-3 / VC-3 carrying an E3.
1 × DS3 ITU-T G.707Client mappingOne VC-3 carrying a DS3.
21 × E1 ITU-T G.707One VC-3 holds 7 TUG-2 × 3 TU-12 (E1).