SONET stand for Synchronous Optical NETwork

SONET ANSI A ISI It is developed By ANSI( A merican I nternational S tandard I nstitute). It is a synchronous network using TDM multiplexing. All clocks in this system are locked to a master clock.

SONET It is standardized multiplexing protocols that transfer multiple digital bit streams over optical fiber using Lasers or Light Emitting Diodes (LEDs). Synchronous Optical Networking (SONET) and Synchronous Digital Hierarchy (SDH) is same.

Architecture Signals Devices Connections

Signals STS SONET defines a hierarchy of electrically levels called Synchronous Transport Signal. Each STS level (STS-1 to STS-192) supports a certain data rate, specified in megabits per second. COS OCs Corresponding Optical Signals are called Optical Carriers (OCs). SDHST MSTM SDH specified similar system called Synchronous Transport Module (STM). See table next slide

DEVICES STS Multiplexers/ Demultiplexers STS Multiplexers/ Demultiplexers mark the begining points and endpoints of SONET link. Regenerator Regenerator extent the length of of the links. It is a repeater. Add/Drop Mltiplexer (ADM) Add/Drop Mltiplexer (ADM) allow insertion and extraction of signals. Terminals Terminals is a device that uses the services of a SONET network.For example, in the internet, a terminal can be a router that needs to send packets to another router at hte other side of a SONET networks.

CONNECTIONs Sections Sections is the optical link connecting two neighbour devices: multiplexer to multiplexer, multiplexer or regenerators, regenerators to regenerators. Lines STS Multiplexers to Add/Drop Multiplexer, two Add/Drop Multiplexer, two STS Multiplexers Lines is the portion of hte network betbeen two multiplexers: STS Multiplexers to Add/Drop Multiplexer, two Add/Drop Multiplexer, two STS Multiplexers Paths STS Multiplexers. In simlpe SONET of two STS multiplexers linkes directly to each other, the section, line and path are the same. Paths is the end-to-end portion of the network between two STS Multiplexers. In simlpe SONET of two STS multiplexers linkes directly to each other, the section, line and path are the same.

SONET Layers The SONET standard includes four functional layers: Photonic Photonic Section Section Line Line Path Path They corespond to both the physical and data link layers.

P ath Layer The path layer is responsible for the movement of a signal from its optical source to its optical destination. At the optical source, the signal is changed from an electronic form into an optical from, multiplexed with other signals, and encapsulated in a frame. At the optical destination the received frame is demultiplexed, and the individual optical signal are changed back into their electronic forms. Path layer overhead is added at this layer. STS multiplexed provide path layer functions.

Line Layer Line layer is responsible for the movement of a signal across a physical line. Line layer overhead is added to a frame at this layer. STS multiplexers and add/drop multiplexers provide line layer functions.

Section Layer Section layer is responsible for the movement of a signal across a physical line. It handles framing, scrambling, and error control. Section layer overhead is added to a frame at this layer.

Photonic Layer Photonic Layer corresponds to the physical layer of the OSI model. Its include the physical specifications for the optical fiber channel, the sensitivity of the receiver, multiplexing functions and so on. SONET uses encoding with the presence of the light representing 1 and the absence of light representing 0.

Device-Layer Relationships Following fig show the relationship between the devices used in SONET transmission and four layers of the standard. As we can see STS multiplexer is a four-layer device. An add/drop multiplexer is a three-layer device. Regenerator is a two-layer device.