High-speed fiber-optic connections are measured in Optical Carrier or "OC" transmission rates. These rates include several standardized bandwidth amounts supported by Synchronous Optical Networking (SONET) connections. They are generically referred to as OCx, where the "x" represents a multiplier of the basic OC-1 transmission rate, which is 51.84 Mbps.
The following is a list of standardized Optical Carrier (OC) data transmission rates. The "STM" numbers in parentheses are the OC equivalents defined in the Synchronous Digital Hierarchy (SDH). The STM numbers are commonly used to define the bandwidth supported by high-speed networking hardware.
- OC-1 (STM-0) - 51.84 Mbps
- OC-3 (STM-1) - 155.52 Mbps
- OC-9 (STM-3) - 466.56 Mbps
- OC-12 (STM-4) - 622.08 Mbps
- OC-18 (STM-6) - 933.12 Mbps
- OC-24 (STM-8) - 1244.16 Mbps
- OC-36 (STM-12) - 1866.24 Mbps
- OC-48 (STM-16) - 2488.32 Mbps
- OC-192 (STM-64) - 9953.28 Mbps
- OC-768 (STM-256) - 40 Gbps
- OC-3072 (STM-1024) - 160 Gbps
As you can see from the list above, the number following "OC-" servers as a multiplier of the basic OC-1 rate of 51.84 Mbps. For example, OC-3 is 51.84 Mbps x 3, or 155.52 Mbps. OC-12 is 4 times that of the OC-3 rate (155.52 Mbps x 4), which is 622.08 Mbps.
OC rates are used to measure speeds of high-speed optical networks, from local business-to-business connections, to the highest bandwidth connections used for the Internet backbone. Small and medium sized businesses that require high-speed Internet connectivity may use OC-3 or OC-12 connections. ISPs that require much larger amounts of bandwidth may use one or more OC-48 connections. Generally, OC-192 and greater connections are used for the Internet backbone, which connects the largest networks in the world together.