SONET—Synchronous Optical Network

SONET equipment and software enable network providers to carry traffic from many types of customer equipment in a uniform way on backbone fiber optic cabling. The high-speed portion of carriers' networks is called the backbone or core, which is analogous to an interstate highway over which many on ramps feed traffic. Without service such as SONET, network providers would be faced with having to monitor and carry traffic in multiple formats and speeds. For example, they would have to have facilities for T-3 and ATM from multiple sources. With a SONET core, their operations, provisioning, monitoring and maintenance functions can be done uniformly and efficiently.

SONET is a standard way to multiplex (see Chapter 1 for multiplexing) high-speed traffic from multiple vendors' multiplexers onto fiber optic cabling. Multiplexing combines traffic from multiple sources onto one line. SONET is a layer 1 transport service used on fiber optic cabling. Layer 1 functions define interfaces to physical media such as copper and fiber optic cabling. SONET takes data and transports it at high speeds called OC (optical carrier) speeds. In contrast, ATM is a Layer 2 service; it performs switching, addressing and error checking. SONET links carry data from ATM switches, IP networks, T-1 and T-3 multiplexers from close to where they enter carrier networks to fiber optic core networks.