synchronous optical networks sonet - wpirek/undergrad_nets/b07/sonet.pdf · • in the 1980’s...
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Telephone NetworksTelephone Networks{Brief History}{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.
2Networks: SONETNetworks: SONET
North American Digital Hierarchy
28
M13Multiplex
M23Multiplex
x7
PrimaryMultiplexEg. DigitalSwitch24 chan PCM
M12Multiplex
x4
1
DS3 44.736 Mbps
DS1 1.544 Mbps DS2 6.312 Mbps DS3 44.736 Mbps
PrimaryMultiplexEg. DigitalSwitch30 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
Copyright ©2000 The McGraw Hill Companies Leon-Garcia & Widjaja: Communication Networks Figure 4.5
3Networks: SONETNetworks: 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.
5Networks: SONETNetworks: 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.
6Networks: SONETNetworks: SONET
SONET and SDH multiplex rates.
Figure 2Figure 2--37. SONET and SDH37. SONET and SDHMultiplex RatesMultiplex Rates
8Networks: SONETNetworks: SONET
Low-SpeedMappingFunction
MediumSpeed
MappingFunction
High-Speed
MappingFunction
DS3
44.736
DS1DS2
CEPT-1
CEPT-4
139.264
ATM150 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
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies Figure 4.8
9Networks: SONETNetworks: SONET
SynhcronousSynhcronous MultiplexingMultiplexingin SONETin SONET
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
ByteInterleave
STS-3
IncomingSTS-1 Frames
Synchronized NewSTS-1 Frames
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies Figure 4.17
10Networks: SONETNetworks: 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.
12Networks: SONETNetworks: SONET
SONET RingSONET Ringa
b
c
d
a
b
c
d ADM
ADM
ADM
ADM
(a) Dual ring (b) Loop-around in response to fault
Leon-Garcia & Widjaja: Communication Networks Figure 4.12Copyright ©2000 The McGraw Hill Companies
13Networks: SONETNetworks: SONET
MUX DEMUX MUX DEMUX
MUX DEMUX
(a) pre-SONET multiplexing
removetributary
inserttributary
ADM
removetributary
inserttributary
(b) SONET Add-Drop multiplexing
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies Figure 4.9
15Networks: SONETNetworks: SONET
SONET RingSONET Ring
Inter-OfficeRings
MetroRing
RegionalRing
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies Figure 4.13
16Networks: SONETNetworks: SONET
Gigabit ATM Applications Over10 Gb/s SONET Ring
Washington U. St Louis 1995
(a) STSPTE
LTESTE
STS-1 Path
STS LineSection Section
Mux Muxreg reg regSONETTerminal
STE STELTE
STSPTE
SONETTerminal
SONET ArchitectureSONET Architecture
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
(b)
optical
section
optical
sectionoptical
section
optical
sectionline
optical
sectionline
optical
sectionlinepath
optical
sectionlinepath
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies Figure 4.14
18Networks: SONETNetworks: SONET
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.
20Networks: SONETNetworks: SONET
SONET FrameSONET Frame
B BB 87B
InformationPayload 9 Rows
125 µsTransportoverhead
90 bytes
3 rows
6 rows
SectionOverhead
LineOverhead
SPE Synchronous Payload Envelope
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies Figure 4.15
23Networks: SONETNetworks: SONET
Two back-to-back SONET frames.
Figure 2Figure 2--36. Two Back36. Two Back--toto--BackBackSONET FramesSONET Frames
24Networks: SONETNetworks: SONET
SPE straddling SONET FrameSPE straddling SONET Frame
Pointer87 columns
9rows
first column is path overhead
SynchronousPayloadEnvelope
framek
framek+1
Pointer
first octet
last octet
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies Figure 4.16
25Networks: SONETNetworks: SONET