SONET/SDH are point-to-point synchronous networks that use TDM multiplexing across a ring or mesh physical topology. These provide the Physical layer foundation for FDDI, SMDS, and ATM implementations.
SONET is the synchronous optical network. It was introduced by Bell Communications in 1984 and quickly accepted by American National Standards Institute (ANSI). In 1988, the Consultative Committee for International Telegraph and Telephony (CCITT) published a similar set of standards called synchronous digital hierarchy (SDH). The International Committee regionalized the standards for international differences in Europe, Japan, and North America.
SONET/SDH are true optical implementations. They take advantage of the bandwidth and high reliability of the fiber optic medium. Because they are typically WAN standards, SONET/SDH use point-to-point connection types. The point-to-point architecture makes the standards ideal for high and centralized systems or WAN backbones. In addition, they use time division multiplexing over a mesh or ring physical topology. SONET/SDH are the physical foundation for various high-end implementations, including:
Finally, SONET/SDH communications support various data rates ranging from Level One (51.84 Mb/s) to Level Twelve (622.08 Mb/s) all the way up to Level Forty-Eight (2.488 Gb/s).
SONET (Synchronous Optical Networking) and SDH (Synchronous Digital Hierarchy) are standardized protocols used to transfer multiple digital bit streams over optical fiber using lasers or light-emitting diodes (LEDs). Initially developed in the mid-1980s, these technologies were designed to replace the older digital hierarchy and to provide a universal standard for synchronous data transmission.
The primary purpose of SONET and SDH is to enable the transmission of large amounts of data over long distances with minimal signal degradation. They are both methods of multiplexing, which means they can combine multiple digital signals into a single optical signal for transmission. Upon reaching their destination, these signals are then demultiplexed, or separated back into their original forms.
While SONET and SDH are similar in purpose and function, they differ mainly in their geographical usage and framing structure. SONET is primarily used in North America and Japan, whereas SDH is more commonly used in the rest of the world. The framing structure of SONET and SDH also differs slightly in terms of hierarchy and data rates, but essentially, they achieve the same goal of high-capacity data transmission over fiber optic networks.
In modern networks, SONET and SDH are still used, particularly in the backbone of telecom networks, but they are increasingly being supplemented or replaced by newer technologies like Dense Wavelength Division Multiplexing (DWDM) and Ethernet-based systems that can offer higher capacities and more flexibility for data services.