Synchronous Optical Networks
SONET
Synchronous Optical Networks
SONET
Advanced Computer Networks
Telephone Networks {Brief History}
Telephone Networks {Brief History}
Digital carrier systems– The hierarchy of digital signals that the telephone
network uses.– Trunks and access links organized in DS (digital
signal) hierarchy– Problem: rates are not multiples of each other.
In the 1980’s Bellcore developed the Synchronous Optical Network (SONET) standard.
Previous efforts include: ISDN and BISDN.
2Advanced Computer Networks SONET
North American Digital Hierarchy
PrimaryMultiplexEg. Digital
Switch30 chan PCM
4th orderMultiplex
x4
2nd orderMultiplex
x4
3rd orderMultiplex
x4
34.368 Mbps2.048 Mbps 8.448 Mbps139.264 Mbps
CEPT 1CEPT 4
European Digital Hierarchy
28
M13Multiplex
M23Multiplex
x7
PrimaryMultiplexEg. Digital
Switch24 chan PCM
M12Multiplex
x4
1
DS3 44.736 Mbps
DS1 1.544 Mbps DS2 6.312 Mbps DS3 44.736 Mbps
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4Advanced Computer Networks SONET
SONETSONETSONET:: encodes bit streams into optical
signals propagated over optical fiber. SONET defines a technology for carrying many signals of different capacities through a synchronous, flexible, optical hierarchy.
A bit-way implementation providing end-to-end transport of bit streams.
All clocks in the network are locked to a common master clock so that simple TDM can be used.
Multiplexing done by byte interleaving. SONET is backward compatible to DS-1 and
E-1 and forward compatible to ATM cells. Demultiplexing is easy.
5Advanced Computer Networks SONET
SONETSONET
Transmission links of the telephone network have been changing to SONET where rates are arranged in STS (Synchronous Transfer Signal) hierarchy.
The hierarchy is called SDH (Synchronous Digital Hierarchy) defined by CCITT.
It is an ITU standard.Advanced Computer Networks SONET 6
Advanced Computer Networks SONET 7
SONET RatesSONET Rates
Advanced Computer Networks SONET 8
Figure 2-37. SONET and SDH
Multiplex Rates
Figure 2-37. SONET and SDH
Multiplex RatesTanenbaum
Low-SpeedMappingFunction
MediumSpeed
MappingFunction
High-Speed
MappingFunction
DS3
44.736
DS1
DS2
CEPT-1
CEPT-4
139.264
ATM
150 Mbps
STS-1
STS-1
STS-1STS-1STS-1
STS-1STS-1STS-1
STS-3c
STS-3c
OC-n
Scrambler
E/O
51.84 Mbps
High-Speed
MappingFunction
MuxSTS-n
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SONET MultipexingSONET Multipexing
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STS-1 STS-1
STS-1 STS-1
STS-1 STS-1
Map
Map
Map
STS-1 STS-1
STS-1 STS-1
STS-1 STS-1
Byte
Inte
rleave
STS-3
IncomingSTS-1 Frames
Synchronized NewSTS-1 Frames
SONET Synchronous Multiplexing
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11Advanced Computer Networks SONET
SONET ArchitectureSONET Architecture
SONET topology can be a mesh, but most often it is a dual ring.
Standard component of SONET ring is an ADM (Add/Drop Multiplexer)– Drop one incoming multiplexed stream
and replace it with another stream.– Used to make up bi-directional line
switching rings.
12Advanced Computer Networks SONET
a
b
c
d
a
b
c
d
(a) Dual ring
(b) Loop-aroundin response to fault
ADM
ADM
ADM
ADM
SONET Ring
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SONET Ring
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MUX DEMUX MUX DEMUX
MUX DEMUX
(a) pre-SONET multiplexing
removetributary
inserttributary
ADM
removetributary
inserttributary
(b) SONET Add-Drop multiplexing
MUX
ADM ADM
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Inter-OfficeRings
MetroRing
RegionalRing
SONET Ring
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Gigabit ATM Over10 Gb/s SONET RingGigabit ATM Over
10 Gb/s SONET Ring
Washington U. St Louis 1995
17Advanced Computer Networks SONET
STE: Section Terminating Equipment, e.g. a repeaterLTE: Line Terminating Equipment, e.g. a STS-1 to STS-3 multiplexerPTE: Path Terminating Equipment, e.g. an STS-1 multiplexer
optical
section
optical
section
optical
section
optical
sectionline
optical
sectionline
optical
section
line
path
optical
section
line
path
(a)
(b)
STSPTE
LTESTE
STS-1 Path
STS LineSection Section
Mux Muxreg reg regSONET
Terminal
STE STELTE
STSPTE
SONET Terminal
SONET ArchitectureSONET Architecture
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SONET Architecture
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Mux = BIM (Byte Interleaved Multiplexer)
Reg = Regenerator
• Boosts power of optical signal• Optical signal is converted to electrical signal.• Amplify electrical signal.• Amplified electrical signal converted back to optical
signal.
20Advanced Computer Networks SONET
SONET Architecture
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Advanced Computer Networks SONET 22
B BB 87B
InformationPayload 9 Rows
125 sTransportoverhead
90 bytes
SectionOverhead 3 rows
6 rowsLine
Overhead
SPE Synchronous Payload Envelope
SONET Frame
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Figure 2-36. Two Back-to-Back
SONET Frames
Figure 2-36. Two Back-to-Back
SONET Frames24Advanced Computer Networks SONET
SONET Frame
Tanenbaum
Pointer87 columns
9rows
first column is path overhead
SynchronousPayload
Envelope
framek
framek+1
Pointer
first octet
last octet
SPE straddling SONET Frame
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ATM Cells in an STS-3 Frame
26Advanced Computer Networks SONET