Result: standard mapping
How many OC-3s are in an OTU4?
An OTU4 carries 640 OC-3s, per ITU-T G.709 and Telcordia GR-253. This path maps OC-192 into ODU2 as a client, then follows that client's tributaries.
640
OC-3s in an OTU4
Working
OTU4 → 1 × ODU4 → 10 × ODU2 → 1 × OC-192 → 64 × OC-3
- 1 × ODU4 in each OTU4 ITU-T G.709The OTU4 frame carries exactly one ODU4.
- 10 × ODU2 in each ODU4 ITU-T G.709Ten ODU2s use all 80 tributary slots, eight slots each.
- 1 × OC-192 in each ODU2 ITU-T G.709Client mappingCBR OC-192, the same client rate as STM-64, mapped into OPU2.
- 64 × OC-3 in each OC-192 Telcordia GR-25364 × OC-3. Channelized OC-192 is 192 STS-1s.
- 1 ODU4
- 1 × 10 = 10 ODU2s
- 1 × 10 × 1 = 10 OC-192s
- 1 × 10 × 1 × 64 = 640 OC-3s
Leftover capacity
12.277173568 Gbit/s of each OTU4 line rate (111.809973568 Gbit/s) sits outside 640 × 155.520 Mbit/s of OC-3 line rate (99.532800 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 718.94, which floors to 718 OC-3s by bit rate only. The standard mapping is 640. Use the mapping.