Result: standard mapping
How many E1s are in a STM-1?
A STM-1 carries 63 E1s, per ITU-T G.707.
63
E1s in a STM-1
Working
STM-1 → 63 × E1
- 63 × E1 in each STM-1 ITU-T G.70763 VC-12 tributaries: 3 TUG-3 × 7 TUG-2 × 3 TU-12.
- 63 E1s
Leftover capacity
26.496 Mbit/s of each STM-1 line rate (155.520 Mbit/s) sits outside 63 × 2.048 Mbit/s of E1 line rate (129.024 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 75.93, which floors to 75 E1s by bit rate only. The standard mapping is 63. Use the mapping.