Result: standard mapping
How many E4s are in an OTU3?
An OTU3 carries 256 E4s, per ITU-T G.709 and ITU-T G.707. This path maps STM-256 into ODU3; E4 into STM-1 as a client, then follows that client's tributaries.
256
E4s in an OTU3
Working
OTU3 → 1 × ODU3 → 1 × STM-256 → 256 × STM-1 → 1 × E4
- 1 × ODU3 in each OTU3 ITU-T G.709The OTU3 frame carries exactly one ODU3.
- 1 × STM-256 in each ODU3 ITU-T G.709Client mappingCBR STM-256 mapped into OPU3.
- 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.
- 1 ODU3
- 1 × 1 = 1 STM-256
- 1 × 1 × 256 = 256 STM-1s
- 1 × 1 × 256 × 1 = 256 E4s
Leftover capacity
7.366829559 Gbit/s of each OTU3 line rate (43.018413559 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 308.89, which floors to 308 E4s by bit rate only. The standard mapping is 256. Use the mapping.