SONET / SDH
Nirmala Shenoy
Information Technology Department
Rochester Institute Technology
updated 1/2002
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SONET / SDH
• Scope
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What is SONET/SDH – features
Signal hierarchy
Topologies
SONET components
Layers
Frames
Virtual tributaries
updated 1/2002
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SONET / SDH
• What is SONET / SDH?
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Synchronous Optical Network – ANSI (US)
Synchronous Digital Hierarchy –ITU-T Europe
Similar and compatible
A standard to be used for fibre optics
Recommendation for FOTS equipment
• Fibre Optic Transmission Systems
– Can carry incompatible DS-0, DS1 (Asyn)
updated 1/2002
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SONET / SDH
• What is SONET / SDH?
– Single reference clock
• synchronize transmissions
– Predictability
– Powerful frame – Transmission envelope
• Multiplex channels
– Multiplexed transport mechanism
• Optical based Carrier System
updated 1/2002
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SONET / SDH
• What is SONET / SDH?
– Self healing ring topology
– Consolidate and segregate traffic from different
end-points
– Extensive integrated OAM&P
– Backward compatibility
updated 1/2002
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SONET / SDH
• Signal Hierarchy
– STS – Synchronous Transport Signals
• support a certain base data rate- 51.84Mbps
• STS 1 – STS 192 – different hierarchies
– Corresponding carrier System
• Optical Carrier – OC-1, OC-3, OC-12, OC-48
– SDH – STM – Synchronous Transport Module
• STM 1 = STS 3
updated 1/2002
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SONET / SDH
• Sonet/SDH rates
STS 1
STS-3
STS-9
STS-12
STS-18
STS-24
STS-36
STS-48
STS-96
STS-192
OC-1
OC-3
OC-9
OC-12
OC-18
OC-24
OC-36
OC-48
OC-96
OC-192
51.840
155.520
466.560
622.080
933.120
1244.160
1866.230
2488.320
4976.640
9953.280
updated 1/2002
STM-1
STM-3
STM-4
STM-6
STM-8
STM-12
STM-16
STM-32
STM-64
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SONET / SDH
• Configuration
Add/drop mux
STS MUX
STS MUX
regenerator
regenerator
section
section
line
path
updated 1/2002
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SONET / SDH
• SONET topology
ADM
SMD
Oc-n
SMD
SA
ADM
Oc-n
DS1
Oc-n
ADM
ADM – add drop
multiplexer
SMD- sts mu/demux
DCS – digital cross
connect switch
SA – service adapter
SMD
Oc-n
DCS
Oc-n
SA
ADM
802.5
Oc-n
SMD
ADM
SMD
updated 1/2002
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SONET / SDH
• Multiplexing
DS1, CEPT1
etc
DS3
MAN, ATM,
SMDS, others
Service
Adapters
Service
Adapters
Service
Adapters
Maps into virtual
tributaries
STS-n
STS-1
MUX/DMUX
E/O
STS-n
updated 1/2002
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SONET / SDH
• SONET Devices
• STS Multiplexer
– Multiplexes and de-multiplexes signals from
multiple sources
– Path terminating equipment
– Maps user payload into standard frame
– Header goes end-to-end as part of Synchronous
Payload Envelope - SPE
updated 1/2002
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SONET / SDH
• SONET Devices
• Add /Drop Multiplexer
– Adds signals from different sources/removes
– Uses header address information to identify
stream and remove
– Line terminating Equipment
– Performs multiplexing, synchronization, APS
updated 1/2002
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SONET / SDH
• SONET Devices
• Regenerator
– Repeater – improves signal quality
– Operations – include layer 2
• Frame alignment, scrambling, error monitoring
– Section terminating equipment
updated 1/2002
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SONET / SDH
• Section
– Connects two neighboring devices
• Line
– Connects two multiplexers (STS , Add/Drop)
• Path
– Connects two STS Mux/demux
• Layers – likewise – path, line, section
updated 1/2002
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SONET / SDH
• SONET layers
PATH layer
LINE layer
Data link
SECTION layer
photonic layer
Physical
updated 1/2002
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SONET / SDH
• Photonic layers – phy
– Specs for optical fiber channel
– NRZ encoding used
• Power level
• Wavelength
• Pulse shape
updated 1/2002
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SONET / SDH
• Section layer
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Frames – identifies beginning of frame
Scrambling – introducing 1’s to derive clock
error monitoring – section level
Adds 9 bytes to header – frame size 810 bytes
Provided at all devices
updated 1/2002
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SONET / SDH
• Line layer
– Locates partial payload – virtual tributaries
– Provides frequency justification, bit stuffing
• To adjust to clocking from different systems
– Does APS
– Adds 18 bytes to header
– Provided at the STS Mux and Add/Drop Mux
updated 1/2002
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SONET / SDH
• Path layer
– Converts to optical signals and back to
electromagnetic
– Adds 9 bytes to header - is part of SPE
– Defines the payload being carried
– End-to-end path control
– Support virtual tributaries
– Provided at the STS Mux
updated 1/2002
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SONET / SDH
• SONET STS-1Frame
Frame1
Frame2
Frame8000
Frame = 810 octets * 8 = 6480bits
8000 frames/sec = 6480*8000 bits/sec = 51.84Mbps
updated 1/2002
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SONET / SDH
• SONET Frame
– Matrix of nine rows – 90 octets each
– First 3 columns (octets) – three rows
• section overhead – 9 bytes
– Next 6 rows – line overheads – 18 bytes
– Rest of the frame – Synchronous Payload
Envelope – SPE – 9 bytes of path overheads
updated 1/2002
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SONET / SDH
– first column in SPE – path overhead
Section
overhead
STS SPE
line
overhead
Path overhead
updated 1/2002
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SONET / SDH
• Section overhead
– Alignment bytes (A1 & A2)– framing and
synchronization – pattern F628hex
– Identification byte (C1)–unique id for the STS1 frame
– Parity byte (B1)
– Order-wire byte (E1)– bytes in consecutive
frames – form a communication channel
between regenerators
updated 1/2002
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SONET / SDH
• Section overhead
– User’s byte (F1)– bytes in consecutive frames
form a channel for user needs at the section
level
– Management bytes (D1, D2 and D3)- 3 bytes
per frame in consecutive frames = 192 kbps for
OAM
updated 1/2002
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SONET / SDH
• Line Overhead
– Pointer bytes (H1, H2, H3)– 3 bytes – identify
location of the payload
– Line Parity byte (B2)
– Automatic Protection Switching bytes 2 bytes
(K1, K2) – consecutive frames- 128 kbps
channel to detect problems in multiplexers
updated 1/2002
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SONET / SDH
• Line Overhead
– Data communication channel bytes (D4-D12) –
consecutive frames – 576 kbps OAM at the line
– Growth bytes (Z1, Z2) – future use
– Orderwire byte (E2) – line level
updated 1/2002
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SONET / SDH
• Path Overhead
– Path trace byte (J1) – bytes in consecutive
frames – path tracking – verify connection
– Path parity byte (B3)
– Path signal label byte (C2) – path id – gives the
construction details of the SPE
– Path Status byte (G1) –receiver communicates
its status
updated 1/2002
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SONET / SDH
• Path Overhead
– Path user channel byte (F2) user needs at path
level
– Virtual tributary indicator (H4) –multi-frame
indicator – payload not fitting into a frame
– Growth byte (Z3, Z4, Z5) – reserved
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updated 1/2002
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SONET / SDH
• Virtual Tributaries
– Partial payload share a frame
– The SPE has a number of tributaries
– VT1.5 = 8000 frames * 3 columns * 9 rows * 8
bits = 1.728 Mbps DS-1 service
– VT2 = 8000 frames*4 columns*9 rows * 8 bits
= 2.304 Mbps CEPT-1
updated 1/2002
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SONET / SDH
• Virtual Tributaries
– VT3 = 8000 frames * 6 columns * 9 rows * 8
bits = 3.456 Mbps DS-1C
– VT6 = 8000 frames*12 columns*9 rows * 8
bits = 6.912 Mbps DS-2
updated 1/2002
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SONET / SDH
• Summary
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A carrier system – optical carriers
Synchronous transmission - faster
Time Division multiplexing
High speed backbone
Support for high bit rate applications?
Add/Drop multiplexers
Self healing rings
updated 1/2002
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