graph explaining sonetSONET (Synchronous Optical Network) is a standard for connecting fiber-optic transmission systems allowing data streams at different rates to be multiplexed. SONET establishes Optical Carrier (OC) levels from 51.8 Mbps (OC-1) to 9.95 Gbps (OC-192).

If you are interested in deploying a SONET network, or want to know OCx availability in your area and what the different carriers charge, we invite you to speak with one of our engineers.

One of SONET's main advantages is its support for a ring topology enabling a self healing network. The working ring takes care of all the traffic while a secondary protection ring remains standby until the working ring fails. SONET will automatically detect the failure in the working ring and transfer control to the protection ring within a fraction of a second. That is why a SONET network can also be seen as a self healing network.

Not all SONET networks are "created equally" and there is a lot of difference as to how they are deployed. One very important fact to consider is the physical locations of the rings or paths; the more physically seperated the routes are, the less chance of a problem with both fiber strands at the same time, taking the network down.

Besides in a ring topology, SONET can also be deployed in a single strand, linear network architecture.

Optical Carrier specifications

Optical Carrier classifications are based on the abbreviation OC followed by a number specifying a multiple of 51.84 Mbit/s: n × 51.84 Mbit/s => OC-n. For example, an OC-3 transmission medium has 3 times the transmission capacity of OC-1.


OC-1 is a SONET line with transmission speeds of up to 51.84 Mbit/s using optical fiber.


OC-3 is a network line with transmission data rate of up to 155.52 Mbit/s using fiber optics. Depending on the system OC-3 is also known as STS-3 (electrical level) and STM-1 (SDH).

OC-3c / STM-1

OC-3c ("c" stands for "concatenated") concatenates three STS-1 (OC-1) frames into a single OC-3 look alike stream.

OC-12 / STM-4

OC-12 is a network line with transmission speeds of up to 622.08 Mbit/s,  often used by ISPs as Wide area network (WAN) connections.


OC-24 is a network line with transmission speeds of up to 1244.16 Mbit/s

OC-48 / STM-16 / 2.5G SONET

OC-48 is a network line with transmission speeds of up to 2488.32 Mbit/s


OC-192 / STM-64 / 10G SONET

OC-192 is a network line with transmission speeds of up to 9953.28 Mbit/s (payload: 9621.504 Mbit/s (9.621504 Gbit/s); overhead: 331.776 Mbit/s).

A standardized variant of 10 Gigabit Ethernet (10GbE), called WAN-PHY, is designed to inter-operate with OC-192 transport equipment while the common version of 10GbE is called LAN-PHY (which is not compatible with OC-192 transport equipment in its native form). The naming is somewhat misleading, because both variants can be used on a wide area network.

OC-768 / STM-256

OC-768 is a network line with transmission speeds of up to 39,813.12 Mbit/s

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