Result: standard mapping
How many STM-1s are in an OTU3?
An OTU3 carries 256 STM-1s, 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.
256
STM-1s in an OTU3
Working
OTU3 → 1 × ODU3 → 1 × STM-256 → 256 × STM-1
- 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 ODU3
- 1 × 1 = 1 STM-256
- 1 × 1 × 256 = 256 STM-1s
Leftover capacity
3.205293559 Gbit/s of each OTU3 line rate (43.018413559 Gbit/s) sits outside 256 × 155.520 Mbit/s of STM-1 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 276.61, which floors to 276 STM-1s by bit rate only. The standard mapping is 256. Use the mapping.