Result: standard mapping
How many E4s are in a STM-256?
A STM-256 carries 256 E4s, per ITU-T G.707. This is a client mapping of E4 into STM-1.
256
E4s in a STM-256
Working
STM-256 → 256 × STM-1 → 1 × E4
- 256 × STM-1 in each STM-256 ITU-T G.707256 × STM-1.
- 1 × E4 in each STM-1 ITU-T G.707Client mappingAsynchronous E4 mapped into the C-4 / VC-4. This client holds 64 E1s internally; the VC-12 tributary count of an STM-1 is 63.
- 256 STM-1s
- 256 × 1 = 256 E4s
Leftover capacity
4.161536 Gbit/s of each STM-256 line rate (39.813120 Gbit/s) sits outside 256 × 139.264 Mbit/s of E4 line rate (35.651584 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 285.88, which floors to 285 E4s by bit rate only. The standard mapping is 256. Use the mapping.