Result: standard mapping
How many DS1s are in a STM-256?
A STM-256 carries 21,504 DS1s, per ITU-T G.707.
21,504
DS1s in a STM-256
Working
STM-256 → 256 × STM-1 → 84 × DS1
- 256 × STM-1 in each STM-256 ITU-T G.707256 × STM-1.
- 84 × DS1 in each STM-1 ITU-T G.70784 VC-11 tributaries: 3 TUG-3 × 7 TUG-2 × 4 TU-11.
- 256 STM-1s
- 256 × 84 = 21,504 DS1s
Leftover capacity
6.610944 Gbit/s of each STM-256 line rate (39.813120 Gbit/s) sits outside 21,504 × 1.544 Mbit/s of DS1 line rate (33.202176 Gbit/s). That remainder is overhead, fixed stuff or justification. It is not another whole tributary.
By bit rate only
Dividing the line rates gives 25,785.69, which floors to 25,785 DS1s by bit rate only. The standard mapping is 21,504. Use the mapping.