Data Communications, Kwangwoon University17-1 Chapter 17. SONET/SDH 17.1 Architecture 17.2 SONET Layers 17.3 SONET Frames 17.4 STS Multiplexing 17.5 SONET.

Data Communications, Kwangwoon University

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Chapter 17. SONET/SDH

17.1 Architecture17.2 SONET Layers17.3 SONET Frames17.4 STS Multiplexing17.5 SONET Networks17.6 Virtual Tributaries

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SONET/SDH

• Digital transmission standards for fiber-optic cable

• Independently developed in USA & Europe

– SONET(Synchronous Optical Network) by ANSI

– SDH(Synchronous Digital Hierarchy) by ITU-T

• Synchronous network using synchronous TDM multiplexing

• All clocks in the system are locked to a master clock

• It contains the standards for fiber-optic equipments

• Very flexible to carry other transmission systems (DS-0, DS-1, etc)

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SONET/SDH Architecture

• Architecture of a SONET system: signals, devices, and connections

• Signals: SONET(SDH) defines a hierarchy of electrical signaling levels called STSs(Synchronous Transport Signals, (STMs)). Corresponding optical signals are called OCs(Optical Carriers)

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SONET/SDH Architecture

• SONET devices: STS multiplexer/demultiplexer, regenerator, add/drop multiplexer, terminals

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SONET/SDH Architecture

• Connections: SONET devices are connected using sections, lines, and paths

• Section: optical link connecting two neighbor devices: mux to mux, mux to regenerator, or regenerator to regenerator

• Lines: portion of network between two multiplexers

• Paths: end-to-end portion of the network between two STS multiplexers

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SONET Layers

• SONET defines four layers: path, line, section, and photonic

• Path layer is responsible for the movement of a signal from its optical source to its optical destination

• Line layers is for the movement of a signal across a physical line

• Section layer is for the movement of a signal across a physical section, handling framing, scrambling, and error control

• Photonic layer corresponds to the physical layer of OSI model

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Device-Layer Relationship in SONET

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SONET Frames

• Each synchronous transfer signal STS-n is composed of 8000 frames. Each frame is a two-dimensional matrix of bytes with 9 rows by 90 × n columns.

• A SONET STS-n signal is transmitted at 8000 frames per second

• Each byte in a SONET frame can carry a digitized voice channel

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SONET Frames

• In SONET, the data rate of an STS-n signal is n times the data rate of an STS-1 signal

• In SONET, the duration of any frame is 125 μs

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SONET Frames: STS-1

• Section overhead () is recalculated for each SONET device

• Line overhead ()

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SONET Frames: SPE

• SPE(Synchronous Payload Envelope) contains the user data and the overhead related to the user data (path overhead)

• Path overhead is only calculated for end-to-end at STS multiplexers

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Overhead Summary

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SPE Encapsulation

• Offsetting of SPE related to frame boundary

• Use of H1 and H2 pointers to show the start of an SPE in a frame

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STS Multiplexing

• STS multiplexing/demultiplexing and byte interleaving

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An STS-3 Frame

• Byte interleaving preserves the corresponding section and line overhead

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Concatenated Signal

• The suffix c (for concatenated) means that the STS-n is not considered as n STS-1 signals. So, it cannot be demultiplexed into n STS-1 signals

• An STS-3c signal can carry 44 ATM cells as its SPE

• SPE of an STS-3c can carry 9 x 260 = 2340 which can accommodate approximately 44 ATM cells, each of 53 bytes

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Add/Drop Multiplexer

• Only remove the corresponding bytes and replace them with the new bytes including the bytes in the section and line overhead

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SONET Network

• Point-to-point network

• Multipoint network

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Automatic Protection Switching

• To create protection against failure in linear networks

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Ring Network: UPSR

• Unidirectional Path Switching Ring (UPSR)

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Ring Network: BLSR

• Bidirectional Line Switching Ring (BLSR)

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Ring Network: Combination

• Combination of UPSR and BLSR

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Mesh Network

• Ring network has the lack of scalability

• Mesh network has better performance

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Virtual Tributaries

• Partial payload that is inserted into an STS-1 frame

• Each component of subdivided SPE

• Provides backward compatibility with the current hierarchy

• Four types of VTs

– VT1.5 : For DS-1(T-1: 1.544Mbps)

– VT2: For European CEPT-1(E-1: 2.048Mbps)

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VT Types