SONET/SDH
Synchronous Optical Network/
Synchronous Digital Hierarchy
SONET was developed by ANSI
SDH was developed by ITU-T
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SONET/SDH Rates
STS
OC
Rate (Mbps)
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-24
OC-24
1244.160
STM-8
STS-36
OC-36
1866.23
STM-12
STS-48
OC-48
2488.320
STM-16
STS-96
OC-96
4976.640
STM-32
STS-192
OC-192
9953.28
STM-64
STS- synchronous Transport Signal
OC- optical carriers
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STM
STM – Synchronous Transport Modules
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Figure 20-1
A SONET System
STS Mux/Demux – beginning & end points
Regenerator – repeater that regenerates the optical signals
Add/drop mux – add signals into a given path or remove a desired signal
from a path
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Figure 20-2
An Example of a SONET Network
Section – optical link connecting 2 neighbor devices
Line – portion of a network between 2 muxes
Path - end to end portion of the network between 2 STS
muxes
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Figure 20-3
SONET Layers
Photonic Layer
-Specs for optical fiber channel,
sensitivity of the receiver
-NRZ – 1-presence of light
Section layer
-Responsible for the movement
of a signal across a physical
section
-Framing, scrambling, error
control
Path layer
-Responsible for the movement of
Line layer
signal from its optical source to its
- STS mux and add/drop mux
optical destination
provide line layer functions
-Transformation of signals
-STS mux provides path layer
functions
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Figure 20-4
Device-Layer Relationship in SONET
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Figure 20-5
Data Encapsulation in SONET
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Figure 20-6
STS-1 Frame
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Figure 20-7
STS-1 Frame Overhead
SPE
– Synchronous payload
envelope
- Contains user data and
details about charges (if
any)
Path overhead
- end-to-end
tracking
information
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Figure 20-8
STS-1 Frame Section Overhead
A1 & A2 – for framing & synchronization, F6 & 28 in hex
C1 – Frame id
B1 – LRC
E1 –used for communication bet. regenerators or bet. terminals & regenerators
F1 reserved for user needs
D1, D2, D3 – for operation, administration and maintenance signaling
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Figure 20-9
STS-1 Frame Line Overhead
H1, H2, H3 – identify the location of the
payload in the frame
K1, K2 – used for automatic detection of
problems in line-terminating equipment
(mux)
Z1, Z2 – reserved for future use
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Figure 20-10
Payload Pointers
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Figure 20-11
STS-1 Frame Path Overhead
J1 – used for tracking the path
C2 – path identification byte, used to identify different
protocols used at higher levels
G1- sent by the receiver to communicate its status to the
sender
F2 – reserved for user needs
H4 – multiframe indicator
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Figure 20-12
Virtual Tributaries
- Partial payload that can be inserted into STS-1 and
combined with other partial payloads to fill out the frames
SONET – backward compatible with the current digital hierarchy (DS-1 to DS
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Figure 20-13
VT Types
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Figure 20-14
Multiplexing STS Frames
STS-n
3 STS-1s = 1 STS-3
4 STS-3s = 1 STS-12
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Figure 20-15
STS Multiplexing
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Figure 20-16
ATM in an STS-3 Envelope
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Applications
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Can replace T-1 or T-3 lines
Can be the carrier for ISDN and B-ISDN
Can be the carrier for ATM cells
Can support bandwidth on demand
Can be used as the backbone or totally
replace other networking protocols such
as FDDI.
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