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

3Advanced Computer Networks SONET

Leon-Garcia & Widjaja: Communication

Networks

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

9Advanced Computer Networks SONET

SONET MultipexingSONET Multipexing

Leon-Garcia & Widjaja: Communication

Networks

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

Advanced Computer Networks SONET 10

Leon-Garcia & Widjaja: Communication

Networks

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

13Advanced Computer Networks SONET

Leon-Garcia & Widjaja: Communication

Networks

SONET Ring

14Advanced Computer Networks SONET

MUX DEMUX MUX DEMUX

MUX DEMUX

(a) pre-SONET multiplexing

removetributary

inserttributary

ADM

removetributary

inserttributary

(b) SONET Add-Drop multiplexing

MUX

ADM ADM

15Advanced Computer Networks SONET

Leon-Garcia & Widjaja: Communication

Networks

Inter-OfficeRings

MetroRing

RegionalRing

SONET Ring

16Advanced Computer Networks SONET

Leon-Garcia & Widjaja: Communication

Networks

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

18Advanced Computer Networks SONET

Leon-Garcia & Widjaja: Communication

Networks

SONET Architecture

19Advanced Computer Networks 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.

20Advanced Computer Networks SONET

SONET Architecture

21Advanced Computer Networks SONET

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

23Advanced Computer Networks SONET

Leon-Garcia & Widjaja: Communication

Networks

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

25Advanced Computer Networks SONET

Leon-Garcia & Widjaja: Communication

Networks

ATM Cells in an STS-3 Frame

26Advanced Computer Networks SONET