Result: standard mapping
How many OC-3s are in an OTU3?
An OTU3 carries 256 OC-3s, per ITU-T G.709 and Telcordia GR-253. This path maps OC-768 into ODU3 as a client, then follows that client's tributaries.
256
OC-3s in an OTU3
Working
OTU3 → 1 × ODU3 → 1 × OC-768 → 256 × OC-3
- 1 × ODU3 in each OTU3 ITU-T G.709The OTU3 frame carries exactly one ODU3.
- 1 × OC-768 in each ODU3 ITU-T G.709Client mappingCBR OC-768, the same client rate as STM-256, mapped into OPU3.
- 256 × OC-3 in each OC-768 Telcordia GR-253256 × OC-3. Channelized OC-768 is 768 STS-1s.
- 1 ODU3
- 1 × 1 = 1 OC-768
- 1 × 1 × 256 = 256 OC-3s
Leftover capacity
3.205293559 Gbit/s of each OTU3 line rate (43.018413559 Gbit/s) sits outside 256 × 155.520 Mbit/s of OC-3 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 OC-3s by bit rate only. The standard mapping is 256. Use the mapping.