Result: standard mapping
How many E1s are in a STM-256?
A STM-256 carries 16,128 E1s, per ITU-T G.707.
16,128
E1s in a STM-256
Working
STM-256 → 256 × STM-1 → 63 × E1
- 256 × STM-1 in each STM-256 ITU-T G.707256 × STM-1.
- 63 × E1 in each STM-1 ITU-T G.70763 VC-12 tributaries: 3 TUG-3 × 7 TUG-2 × 3 TU-12.
- 256 STM-1s
- 256 × 63 = 16,128 E1s
Leftover capacity
6.782976 Gbit/s of each STM-256 line rate (39.813120 Gbit/s) sits outside 16,128 × 2.048 Mbit/s of E1 line rate (33.030144 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 19,440, which floors to 19,440 E1s by bit rate only. The standard mapping is 16,128. Use the mapping.