Chapter 20 SONET/SDH (Synchronous Optical Network /Synchronous Digital Hierarchy)

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Chapter 20SONET/SDH(Synchronous Optical Network
/Synchronous Digital Hierarchy)
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SONET Developed by ANSI

• Set of standards to take advantage of the
  high-speed digital transmission capability of
  fiber optic
• It is a synchronous network
• (a single clock is used to handle the
  synchronization)
• Employed by telephone companies and common
  carriers.
• Its transmission speeds range from 51 Mbps to
  multiple Gigabits per second.

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SDH (Synchronous Digital Hierarchy)

• The European counterpart to SONET
• Developed by ITU-T

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Synchronous Transport Signals(STS)

• SONET specification
• Defines a hierarchy of standardized of 10
  signaling levels. (STS-1 through STS-192)
• Each signaling level supports a certain data
  rate.
• The physical link specifications are referred by
  optical carriers (OCs)

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STS OC Rate (Mbps) STM
STS-1 OC-1 51.840
STS-3 OC-3 155.520 STM-1
STS-9 OC-9 466.560 STM-3
STS-12 OC-12 622.080 STM-4
STS-18 OC-18 933.120 STM-6
STS-21 OC-24 1244.160 STM-8
STS-36 OC-36 1866.230 STM-12
STS-48 OC-48 2488.320 STM-16
STS-96 OC-96 4976.640 STM-32
STS-192 OC-192 9953.280 STM-64
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Observations

• Multiple STS-1 signals can be multiplexed to form
  STS-n signal
• The lowest rate for SDH is 155.52 Mbps.
• The lowest-rate signal to accommodate an ITU-T
  level 4 signal (139.264 Mbps)
• The difference in capacity is needed for overhead
  of the optical system.

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SONET Devices

• STS Multiplexer/Demultiplexer
• Regenerator (repeater)
• Add/Drop Multiplexer

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SONET System and Connections
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Different levels of SONET Connections (Sections,
Lines,and Path)

• Section
• An optical link connecting two neighbors
• Line
• The portion of the network between two
  multiplexers
• Path
• An end-to-end portion of the network between two
  STS Multiplexers

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SONET Layers

• SONET defines four layers
• Photonic layer
• Section layer It provides framing, scrambling,
  and error control. Also responsible for moving
  the signal across a physical section.
• Line layer Responsible for moving the signal
  across a physical line. Multiplexers provide
  these functions.
• Path layer Responsible for moving the signal
  from its optical source to its optical
  destination.

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SONET Layers
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Device-Layer Relationship
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Frame Format

• STS-1 frame is the basic building block for
  SONET.
• Frame size is 810 octets transmitted every 125
  ?sec. (51.84 Mbps)
• Logically can be viewed as a matrix of 9 rows and
  90 columns.
• Transmitted one row at a time from left to right
  and from top to bottom.
• First three columns are used for overhead.

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STS-1 Frame
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STS-1 Overhead
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Virtual Tributaries
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VT Types
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STS-n
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STS Multiplexing
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ATM in an STS-3 Envelope
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SONET Applications

• Designed to provide backbone for WANs
• Can replace T-1 and T-3 lines
• Can be a carrier for ISDN and B-ISDN
• Can be a carrier for ATM cells
• Can support bandwidth on demand