Result: standard mapping
How many DS3s are in a STM-4?
A STM-4 carries 12 DS3s, per ITU-T G.707.
12
DS3s in a STM-4
Working
STM-4 → 4 × STM-1 → 3 × DS3
- 4 × STM-1 in each STM-4 ITU-T G.7074 × STM-1.
- 3 × DS3 in each STM-1 ITU-T G.707Three VC-3s, each able to carry a DS3.
- 4 STM-1s
- 4 × 3 = 12 DS3s
Leftover capacity
85.248 Mbit/s of each STM-4 line rate (622.080 Mbit/s) sits outside 12 × 44.736 Mbit/s of DS3 line rate (536.832 Mbit/s). That remainder is overhead, fixed stuff or justification. It is not another whole tributary.
By bit rate only
Dividing the line rates gives 13.9, which floors to 13 DS3s by bit rate only. The standard mapping is 12. Use the mapping.