Ever wonder just what the heck was an "OC48"? Not surprisingly many network engineers and IT managers aren't up to speed (no pun intended) on just what OC really means...and what all is available to enahnce their company's applications within this bandwidth category.

So....here's a quick run down to set you straight.

The OC (optical carrier...fiber optic based broadband network )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 the network design decisions for your business now....and in the future!