Synchronous Optical Synchronous Optical NetworksNetworksSONETSONET

1Networks: SONETNetworks: SONET

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

Networks: SONETNetworks: SONET4

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

7Networks: 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

11Networks: 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

Networks: SONETNetworks: SONET14

SONET RingSONET Ring

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

SONET ArchitectureSONET Architecture

19Networks: 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

Networks: SONETNetworks: SONET21

Networks: SONETNetworks: SONET22

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

ATM Cells in an STSATM Cells in an STS--3 Frame3 Frame

26Networks: SONETNetworks: SONET