1. Data Communications, Kwangwoon University
Chapter 17. SONET/SDH
17.1 Architecture
17.2 SONET Layers
17.3 SONET Frames
17.4 STS Multiplexing
17.5 SONET Networks
17.6 Virtual Tributaries
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2. Data Communications, Kwangwoon University
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)
Data Communications, Kwangwoon University

3. 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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4. SONET/SDH Architecture
SONET devices: STS multiplexer/demultiplexer, regenerator, add/drop multiplexer, terminals
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5. 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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6. Data Communications, Kwangwoon University
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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7. Device-Layer Relationship in SONET
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8. Data Communications, Kwangwoon University
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
Data Communications, Kwangwoon University

9. Data Communications, Kwangwoon University
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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10. Data Communications, Kwangwoon University
SONET Frames: STS-1
Section overhead () is recalculated for each SONET device
Line overhead ()
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11. Data Communications, Kwangwoon University
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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12. Data Communications, Kwangwoon University
Overhead Summary
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13. Data Communications, Kwangwoon University
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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14. Data Communications, Kwangwoon University
STS Multiplexing
STS multiplexing/demultiplexing and byte interleaving
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15. Data Communications, Kwangwoon University
An STS-3 Frame
Byte interleaving preserves the corresponding section and line overhead
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16. Data Communications, Kwangwoon University
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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17. Data Communications, Kwangwoon University
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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18. Data Communications, Kwangwoon University
SONET Network
Point-to-point network
Multipoint network
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19. Automatic Protection Switching
To create protection against failure in linear networks
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20. Data Communications, Kwangwoon University
Ring Network: UPSR
Unidirectional Path Switching Ring (UPSR)
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21. Data Communications, Kwangwoon University
Ring Network: BLSR
Bidirectional Line Switching Ring (BLSR)
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22. Ring Network: Combination
Combination of UPSR and BLSR
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23. Data Communications, Kwangwoon University
Mesh Network
Ring network has the lack of scalability
Mesh network has better performance
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24. Data Communications, Kwangwoon University
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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25. Data Communications, Kwangwoon University
VT Types
Data Communications, Kwangwoon University