Ever pretend you knew what an OC-48 was? Here's your chance to bone up.
The OC hierarchy goes as follows, starting with a T3/DS3 electrical carrier and then on to an OC-1:
DS3 (Electrical) = 44.736mbits/sec = 28 T1s/DS1s
STS1 (Electrical) = (1) DS3 @ 44.736mbits/sec with SONET (Synchronous Optical NET) overhead = 51.840mbits/sec
OC-1 (Optical) = (1) STS1 on Optical facilities
OC-3 = (3) OC-1s = 155.52mbits/sec
OC-9 = (9) OC-1s (not commonly used) = 466.56mbits/sec
OC-12 = (12) OC-1s or (4) OC-3s = 622.08mbits/sec
OC-18 = (18) OC-1s (not commonly used) = 933.12mbits/sec
OC-24 = (24) OC-1s (not commonly used) = 1.244gbits/sec
OC-36 = (36) OC-1s (not commonly used) = 1.866gbits/sec
OC-48 = (48) OC-1s or (4) OC-12s or (16) OC-3s = 2.488gbits/sec
OC-192= (192) OC-1s or (4) OC-48s or (16) OC-12s or (64) OC-3s = 9.953gbits/sec
The reason for the stair-stepping of the OC Hierarchy is due to the fact that the next available level of multiplexing ('muxing") of lower-level circuits is usually 4: (4) OC-3s = (1) OC-12, and (4) OC-48s = (1) OC-192.
This muxing scheme is usually dictated by the equipment manufacturers and is pretty much an adopted standard in the Telecom industry - hence the lack of the lesser-common bandwidth aggregations like OC-9, OC-18, etc. The only exception is the OC-3, which was needed to allow the upper-level hierarchy to work. Hope this tidbit of info helps in the future!