Result: standard mapping
How many STM-4s are in an OTU3?
An OTU3 carries 64 STM-4s, per ITU-T G.709 and ITU-T G.707. This path maps STM-256 into ODU3 as a client, then follows that client's tributaries.
64
STM-4s in an OTU3
Working
OTU3 → 1 × ODU3 → 1 × STM-256 → 64 × STM-4
- 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.
- 64 × STM-4 in each STM-256 ITU-T G.70764 × STM-4.
- 1 ODU3
- 1 × 1 = 1 STM-256
- 1 × 1 × 64 = 64 STM-4s
Leftover capacity
3.205293559 Gbit/s of each OTU3 line rate (43.018413559 Gbit/s) sits outside 64 × 622.080 Mbit/s of STM-4 line rate (39.813120 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 69.15, which floors to 69 STM-4s by bit rate only. The standard mapping is 64. Use the mapping.