Fiber Optic CommunicationBy

Engr. Muhammad Ashraf Bhutta

History of SONETHistory of SONET•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.Telco's needed to replace aging copper wire Telco's needed to replace aging copper wire networksnetworksTelco's wanted a global standard to connect a fiber Telco's wanted a global standard to connect a fiber optic networkoptic networkSONET first proposed by Bellcore, in 1984SONET first proposed by Bellcore, in 1984Synchronous Digital Hierarchy (SDH) was used in Synchronous Digital Hierarchy (SDH) was used in EuropeEuropeAgreement was made in 1998 to merge the two Agreement was made in 1998 to merge the two similar standardssimilar standards

SONET Protocol HierarchySONET Protocol Hierarchy

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

section

line

optical

section

line

optical

section

line

path

optical

section

line

path

(a)

(b)

STSPTE

LTESTE

STS-1 Path

STS Line

Section Section

Mux Muxreg reg regSONETTerminal

STE STELTE

STSPTE

SONETTerminal

SONET Architecture

SONET Link ArchitectureSONET Link Architecture

3

SONET Multiplexer and Demultiplexer

• The synchronous transport signal level -1 (STS-1) is the basic building block of the SONET hierarchy. A higher-level signal in the hierarchy is obtained through the interleaving of bytes from the lower-level signals. Each STS-n electrical signal has has a corresponding optical carrier level-n (OC-n) signal. The OC-n signals are the same except for the use of scrambling in the optical signal. The SDH standard refers to synchronous transfer modules-n (STM-n) signals and begins at a bit rate of 155.52 Mbps. The SDH STM-1 signal is equivalent to the SONET STS-3 signal.

• Figure shows source multiplexing and demultiplexing. The most important feature to note is that all clocks in the network are locked to a common master clock. Multiplexing in SONET is done by byte interleaving. As a result, if each of N input streams has the same rate R, the multiplexed stream has rate NR. Because sources are synchronized, the buffers at each input line will be very small as they have only to accommodate the effect of jitter.

North American Digital Hierarchy

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

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

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

4

SONET and SDH Digital Hierarchy

SONET electrical signal Optical signal Bit rate (Mbps) SDH Electrical signal

STS-1 OC-1 51.84STS-3 OC-3 155.52 STM- 1STS-9 OC-9 466.56 STM-3STS- 12 OC- 12 622.08 STM-4STS-18 OC-18 933.12 STM-6STS-24 OC-24 1244.16 STM-8STS-36 OC-36 1866.24 STM- 12STS-48 OC-48 2488.32 STM- 16STS- 192 OC- 192 9953.28 STM-64

STS-n: Synchronous Transport Signal Level-nOC-n: Optical carrier Level-nSTM-n: Synchronous Transfer Modules-n

Abbreviation:

SONETSONET:: 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..

• 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.

SONET 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.

a

b

c

d

a

b

c

d

(a) Dual ring (b) Loop-around in response to fault

ADM

ADM

ADM

ADM

SONET Ring

MUX DEMUX MUX DEMUX

MUX DEMUX

(a) pre-SONET multiplexing

removetributary

inserttributary

ADM

removetributary

inserttributary

(b) SONET Add-Drop multiplexing

a

b

c

3 ADMs

physical loop net

OC-3nOC-3n

OC-3n

Inter-OfficeRings

MetroRing

RegionalRing

STS-1 Building BLockSTS-1 Building BLock

STS-1 Building BLockSTS-1 Building BLockBasic building block of SONETBasic building block of SONETRate 51.84Mbps usually depicted 9 rows Rate 51.84Mbps usually depicted 9 rows X 90 columns = 810 8bit bytesX 90 columns = 810 8bit bytesWith a rate of 8000 frames/sec. Each With a rate of 8000 frames/sec. Each frame has a duration of 125 microseconds.frame has a duration of 125 microseconds.At 6480 bits per frame x, 8000 frames a At 6480 bits per frame x, 8000 frames a second equals 51,840,000bps or second equals 51,840,000bps or 51.84Mbps51.84Mbps

SONET Cell MappingSONET Cell Mapping

SONET TopologiesSONET Topologies

Point-to-PointPoint-to-Point•2 devices connected by optical fiber2 devices connected by optical fiber•Entry level PTE for an organizationEntry level PTE for an organization•Inputs/Outputs identicalInputs/Outputs identical

SONET TopologiesSONET Topologies

Point-to-MultipointPoint-to-Multipoint•Uses Add-Drop Multiplexing (ADM) to Uses Add-Drop Multiplexing (ADM) to drop circuits off along the waydrop circuits off along the way•Suitable for large national corporate Suitable for large national corporate networksnetworks

SONET TopologiesSONET TopologiesHub & SpokeHub & Spoke

•Accommodates unexpected growth or change more Accommodates unexpected growth or change more easily than point-to-pointeasily than point-to-point•Hub concentrates traffic at a central site to allow for Hub concentrates traffic at a central site to allow for easy reprovisioning of the circuitseasy reprovisioning of the circuits

SONET TopologiesSONET TopologiesRingRing

•ADM is building block for SONET ring ADM is building block for SONET ring architecture.architecture.•Multiple ADMs within a ring topology can Multiple ADMs within a ring topology can either be bidirecitonal or unidirectionaleither be bidirecitonal or unidirectional•Main advantage is survivability - if a fiber Main advantage is survivability - if a fiber cable is cut, the multiplexers have the cable is cut, the multiplexers have the intelligence send via an alternative path intelligence send via an alternative path through the ring without interruptionthrough the ring without interruption

SONET RingSONET Ring

DCCDCC

ADMADM

ADMADM

ADMADM

DCCDCC

ADMADM

ADMADM

ADMADM

Synchronous Digital Hierarchy (SDH)Synchronous Digital Hierarchy (SDH)

European Standard analogous to the European Standard analogous to the North American SONETNorth American SONETBasic building block is the STM-1 Basic building block is the STM-1 Frame that consists of:Frame that consists of:

270 columns x 9 rows = 2430 octets270 columns x 9 rows = 2430 octets

9 columns x 9 rows = 81 octet section overheads9 columns x 9 rows = 81 octet section overheadsWill be discussed in next lecture(14-05-2005)Will be discussed in next lecture(14-05-2005)

SONET over WDMSONET over WDMSONETSONET

•Single wavelength optical network.Single wavelength optical network.•Uses fiber as transmission media,Uses fiber as transmission media,•Does all switching, routing, Does all switching, routing, processing electronically.processing electronically.

Wavelength Division Multiplexing Wavelength Division Multiplexing (WDM)(WDM)

•Wavelength routingWavelength routing•Carry multiple wavelengths in a Carry multiple wavelengths in a single fibersingle fiber

SONET over WDMSONET over WDM

WADMWADM

WADM

WADM

λ3

λ1

Complete it?

Plesiochronous TransmissionPlesiochronous TransmissionMeans “almost synchronous”Means “almost synchronous”

•Bits are stuffed into the frame as padding Bits are stuffed into the frame as padding when various occur on the timing of the linewhen various occur on the timing of the line

Factors that affect transmission rates over Factors that affect transmission rates over fiber optic lines:fiber optic lines:

•Temperature differences along the cable can Temperature differences along the cable can affect light signaling and clock timing affect light signaling and clock timing •Photonic and Laser technology is a limiting Photonic and Laser technology is a limiting factor in the evolution of higher data rates over factor in the evolution of higher data rates over SONETSONET

Benefits of SONETBenefits of SONETPointers, MUX/DEMUXPointers, MUX/DEMUX

•SONET allows very flexible allocation and SONET allows very flexible allocation and alignment of payload within transmission alignment of payload within transmission envelop.envelop.

Reduced Back-to-Back MultiplexingReduced Back-to-Back Multiplexing•Because of synchronization, an entire optical Because of synchronization, an entire optical signal does not have to be demultiplexed – only signal does not have to be demultiplexed – only the VT or STS signals need to be accessed.the VT or STS signals need to be accessed.

Optical InterconnectivityOptical Interconnectivity•Allows interconnection between network Allows interconnection between network providers regardless of equipment manufacturer.providers regardless of equipment manufacturer.

Benefits of SONETBenefits of SONETMultipoint ConfigurationsMultipoint Configurations

•Network providers no longer need to own and Network providers no longer need to own and maintain customer-located equipmentmaintain customer-located equipment

ATMATM•Because of the bandwidth capacity offered by Because of the bandwidth capacity offered by SONET, it is a logical carrier for ATMSONET, it is a logical carrier for ATM

GroomingGrooming•SONET networks can eliminate inefficient SONET networks can eliminate inefficient techniques like back-hauling, which is expensive to techniques like back-hauling, which is expensive to do on asynchronous systemsdo on asynchronous systems•SONET can also conveniently segregate switched SONET can also conveniently segregate switched and non-switched traffic.and non-switched traffic.

Benefits of SONETBenefits of SONETReduced Cabling & Elimination of DSX Panels

•SONET allows for hub configuration, reducing the need for back-to-back terminals

Enhanced OAM&P•Remote positioning provides centralized maintenance, reduced travel for maintenance personnel, hence reduced savings.

Enhanced Performance Monitoring•SONET allows for quicker troubleshooting and detection of failures before they because of the substantial overhead information.