Synchronous Optical Networking

About

Synchronous optical network (SONET) offers cost-effective transport both in the access area and core of the network. For instance, telephone or data switches rely on SONET transport for interconnection.

Two Types of SONET Ring

There are two types of SONET ring One switches individual paths (path switched) and the other switches the entire optical line capacity (line switched). A key difference is the number of fibers used. Path switched rings use only two fibers while line switching can use either two or four fibers.

Linear Deployment vs. Ring Deployment

SONET operates in several different modes. A major distinction in operation is whether the service is deployed in a linear fashion or as one of several ring types. As shown in figure six, a linear deployment is vulnerable to interruption because the fiber cable has only a single path to the endpoints.

Sonet Hierarchy

Figure  illustrates how signals are carried in SONET. First, SONET packages a signal into containers. It then adds the section overhead so that the signal and the quality of transmission are all traceable. The containers have two names depending on size: virtual tributary (VT) or a synchronous payload envelope (SPE). The path overhead contains data to control the facility (end to end) such as for path trace, error monitoring, far-end error, or virtual container (VC) composition.

Digital Access Cross Connect Systems and Add Drop Multiplexers

SONET systems are accessed within carrier central office equipment through digital access cross connect systems (DACS) which provide the interface between the digital input signal and the backbone SONET channel. The ability to use 'add-drop' capabilities is essential to making SONET a widespread and deploy-able technology.

FDDI And DQDB

The Fiber Distributed Data Interface (FDDI) and the Distributed Queue, Dual Bus (DQDB) protocols are both intended as a Metropolitan Area Network (MAN) solution for high performance requirements. Both FDDI and DQDB use a double ring topology. Both of these approaches impose no restrictive distance limitation, no terminal limits, and no limits on the total span of the network. FDDI is an ANSI standard that operates at the lower level within the OSI IEEE 802 architecture, as does DQDB, the 802.6 standard.

Introduction

High capacity fiber optic facilities and total service consistency are becoming critical aspects of the corpo¬rate enterprise network as businesses become more reliant on high bandwidth data applications. SONET optical interface standards, combined with end-to-end architectures based on four fiber, bi-directional line switched rings, provide the highest possible level of service assurances, while guaranteeing bandwidth ranges to support the most demanding business appli¬cations. This Technology Guide examines the SONET architecture, within the context of a national tail-safe ring structure. It explores the manner in which the four fiber, bi-directional ring approach is uniquely suited to trouble free service, while enabling efficient network management and equipment interoperability.

Conclusion

Synchronous optical network (SONET) is a standard for optical telecommunications transport formulated by the Exchange Carriers Standards Association (ECSA) for the American National Standards Institute (ANSI), which sets industry standards in the U.S. for telecommunications and other industries.