Result: standard mapping
How many E2s are in a STM-4?
A STM-4 carries 48 E2s, per ITU-T G.707 and ITU-T G.702.
48
E2s in a STM-4
Working
STM-4 → 4 × STM-1 → 3 × E3 → 4 × E2
- 4 × STM-1 in each STM-4 ITU-T G.7074 × STM-1.
- 3 × E3 in each STM-1 ITU-T G.707Three VC-3s, each carrying an E3.
- 4 × E2 in each E3 ITU-T G.702Four E2s.
- 4 STM-1s
- 4 × 3 = 12 E3s
- 4 × 3 × 4 = 48 E2s
Leftover capacity
216.576 Mbit/s of each STM-4 line rate (622.080 Mbit/s) sits outside 48 × 8.448 Mbit/s of E2 line rate (405.504 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 73.63, which floors to 73 E2s by bit rate only. The standard mapping is 48. Use the mapping.