telecommunications systems and technology part 4-1

TELECOMMUNICATIONS

SYSTEMS AND TECHNOLOGY

PART 4-1

SONET & SDH

SONET/SDH

1. SONET (USA PROPOSAL/STANDARD)

SYNCHRONOUS OPTICAL NETWORKING

(ORIGINATED BY BELLCORE THE RESEARCH

ARM OF THE RBOCS) AND THEREAFTER IN

CONJUNCTION WITH ANSI

2. SDH (EUROPEAN PROPOSAL/STANDARD)

SYNCHRONOUS DIGITAL HIERARCHY ( CCITT ITU)

WHEN DATA IS TRANSMITTED OVER ACOMMUNICATIONS MEDIUM, VARIOUS TASKSMUST BE PROVIDED ON THE LINK (THIS IS THEDIFFERENCE BETWEEN A DUMB WIRE/GLASS AND ANINTELLIGENT WIRE/GLASS – LINK)

THESE INCLUDE:

1. FRAMING OF THE DATA

2. ERROR CHECKING

3. LINK MANAGEMENT

A COMMUNICATIONS LINK

FOR OPTICAL COMMUNICATIONS THESE FUNCTIONS HAVE BEEN STANDARDIZED BY THE ANSI T1X1.5 COMMITTEE AS SYNCHRONOUS OPTICAL NETWORKING (SONET) AND BY THE ITU AS SYNCHRONOUS DIGITAL HIERARCHY (SDH).

• ANSI: AMERICAN NATIONAL STANDARDS INSTITUTE • ITU: INTERNATIONAL TELECOMMUNICATION UNION

FORMERLY KNOWN AS:

• CCITT: INTERNATIONAL TELEGRAPH AND TELEPHONE CONSULTATIVE COMMITTEE

http://www.itu.int/ITU-T/

USEFUL LINKS

http://www.ansi.org/

http://www.itu.int/home/index.html

ANSI HOME PAGE:

ITU HOME PAGE:

ITU TELECOM PAGE:

SONET Vs SDH

• THERE ARE A LOT OF SIMILARITIES BETWEEN SONET AND SDH, THERE ARE SOME SIGNIFICANTDIFFERENCES, ESPECIALLY IN TERMINOLOGY.

• SONET IS A SUBSET OF SDH AND IT IS EASIER TO INTRODUCE THE TOPIC FROM A SONET POINT OF VIEWAS UNDERSTANDING SONET MAKES IT EASIER TOUNDERSTAND SDH

• FOR EXAMPLE CERTAIN ASPECTS OF SDH EXIST TO MAINTAIN COMPATIBILITY WITH SONET

HISTORY

1. PRE-1960’S

INDIVIDUAL ANALOG LINES BETWEENSWITCHING OFFICES

2. 1962

AT&T DS-1 T1-CARRIER DIGITAL SERVICE

HISTORY

CHANNEL BANK RESIDES IN C.O.

3. POST 1962

AS TIME ELAPSED:

• THE VOLUME OF LONG DISTANCE CALLS INCREASED SUBSTANCIALLY

• THE NUMBER OF T-CARRIER CIRCUITS REQUIRED INCREASED EQUALLY

• THE CAPACITY DEMAND (BANDWITH) INCREASED AS WELL

HISTORY

4. LATE 1970’SHISTORY

• OPTICAL COMMUNICATIONS BECAME FEASIBLE, ALLOWING HIGHER SPEED COMMUNICATIONS(HIGHER TROUGHPUT/BANDWITH – A SYSTEM CAN CARRY MANY MORE TELEPHONE CALLS)

• ONE OF THE FIRST COMMERCIAL FIBER COMMUNICATIONS SYSTEM WAS INSTALLED IN CHICAGO IN 1977 AND OPERATED AT 45 MBPS (DS-3 RATE T3-CARRIER)

HISTORY

MULTPLEXER RESIDES IN C.O.

Multiplexer

Two optical fibers(Tx and Rx)

Multiplexer

HISTORY

• ORIGINALLY, THE TELEPHONE COMPANIES LOOKED AT OPTICAL COMMUNICATIONS AS SIMPLY A REPLACEMENT FOR THE OLDER WIRE OR MICROWAVE COMMUNICATIONS USED FOR YEARS

• VENDORS OF OPTICAL COMMUNICATIONS EQUIPMENT USED THEIR PROPRIETARY FRAMING TECHNIQUES. ONCE AN OPTICAL FIBER VENDOR WAS SELECTED, NO CHOICE REMAINED FOR THE VENDOR OF ALL THE EQUIPMENT IN THAT OPTICAL NETWORK

• ANSI WORK STARTED IN 1985 WITH THE CCITT(NOW CALLED ITU) INITIATING A STANDARDIZATION EFFORT IN 1986

• FROM THE VERY BEGINNING CONFLICT BETWEEN ANSI (US PROPOSALS) AND THE ITU (EUROPEAN PROPOSALS) EXISTED

• STANDARDS IN OPTICAL COMMUNICATIONS BECAME APPARENT

HISTORY

• THE US WANTED A DATA RATE CLOSE TO 50 MBPS IN ORDER TO CARRY DS-1 (1.544 MBPS) AND DS-3 (44.736 MBPS) SIGNALS.

• THE EUROPEANS NEEDED A SPECIFICATION WHICH WOULD CARRY E1 (2.048 MBPS), E3 (34.368 MBPS), AND 139.264 MBPS SIGNALS EFFICIENTLY. SO THEY REJECTED THE 50 MBPS PROPOSAL AND DEMANDED A BASE SIGNAL RATE CLOSE TO 150 MBPS.

HISTORY

EVENTUALLY A COMPROMISE WAS REACHED WHICH ALLOWED THE US SPECIFICATION KNOWN FORMALLY AS SYNCHRONOUS OPTICAL NETWORKING (SONET) WHOSE DATA RATES ARE A SUBSET OF THE ITU SPECIFICATION, KNOWN FORMALLY AS SYNCHRONOUS DIGITAL HIERARCHY (SDH).

HISTORY

HISTORY

ANSI HAS A REPORT WHICH OUTLINES THE MAJOR DIFFERENCES BETWEEN SONET AND SDH [T1RPT36]

SONET/SDH GOALS

• TO ENHANCE SERVICES AND EXISTING TECHNOLOGIES (THE FIRST STANDARDS FOR OPTICAL COMMUNICATIONS WERE FOCUSED ON HANDLING VOICE CIRCUITS SUCH AS DS-1’s/E1’s AND DS-3’s/E3’s)

• TO PROVIDE A COMMON CONNECTIVITY INTERFACE AMONG THE LOCAL EXCHANGES AND THE LONG DISTANCE CARRIER

SONET/SDH GOALS

• ABILITY OF DIFFERENT CARRIERS TO INTERCONNECT

• CONTINUE THE MULTIPLEXING STRUCTURE TO GROW INTO GIGABITS/SEC

• PROVIDE IMPROVEMENTS FOR THE SUPPORT OF OPERATIONS, ADMINISTRATION, AND MAINTENANCE (OAM)

• UNIFY THE U.S, EUROPEAN, AND JAPANESE DIGITAL SYSTEMS, ALL BASED ON THE 64 KBPS PCM CHANNELS (COMBINED IN DIFFERENT (AND INCOMPATIBLE) WAYS)

SONET/SDH BENEFITS

• COMMUNICATION OVER OPTICAL FIBER (OPTICAL TRANSMISSION BETWEEN EO’s IS IMMUNE TO ELECTRICAL INTERFERENCE) • FIBER OPTIC STRANDS (DIAMETER IS CLOSE TO THAT OF A HUMAN HAIR = 125 MICROMETERS) ARE MUCH SMALLER AND LIGHTER THAN COPPER WIRE

• ONLY TWO FIBER STRANDS ARE NEEDED FOR FULL DUPLEX OPERATION AS OPPOSED TO 4 COPPER WIRES

SONET/SDH BENEFITS

• LIGHT PULSES CAN OPERATE AT MUCH HIGHER RATES THAN THAT OF AN ELECTRICAL SYSTEM

• WITH COPPER, THE HIGHEST RATE IN THE US IS THE DS-3 RATE AT 44.736 Mbps

• WITH SONET THE RATE STARTS AT 51.84 Mbps

SONET MUX RATES

LABEL Mbps EQUIVALENT

DS1 DS3

OC-1 51.84 28 1

OC-3 155.52 84 3

OC-9 466.56 252 9

OC-12 622.08 336 12

OC-18 933.12 504 18

OC-24 1244.16 672 24

OC-36 1866.24 1008 36

OC-48 2488.32 1344 48

SONET MUX RATES

LABEL Mbps EQUIVALENT

DS1 DS3

OC-96 4976.64 2688 96

OC-192 9953.28 5376 192

OC-255 13920.0 6120 255

OC-1 OPTICAL CARRIER/LEVEL 1 (51.84 Mbps)

OC-N = (N x 51.84) Mbps

STS-1: SYNCHRONOUS TRANSPORT SIGNAL/LEVEL 1, (51.84 Mbps)OC-1 OPTICAL CARRIER/LEVEL 1 (51.84 Mbps), (STS-1 = OC-1)

SONET/SDH BENEFITS

• SONET’S LIGHT SIGNAL CAN TRAVEL MUCH FURTHERWITHOUT REPEATER THAN ELECTRICAL SIGNALS CANOVER COPPER

• WHILE A DS-3 CIRCUIT NEEDS A REPEATER EVERY 450 FEET, A SONET CIRCUIT WILL NEED A REPEATERAFTER 87.5 MILES

• THE BIT ERROR RATE (BER) FOR SONET (BER = 1 X 10-10) IS MUCH LOWER THAN THAT OF ELECTRICAL SIGNALS OVER COPPER (BER = 1 X 10-6)

SONET/SDH BENEFITS• SONET DATA RATES ARE INTEGER MULTIPLES OFTHE OC-1 DATA RATE.

OC-N STRUCTURE OC-N = (N x 51.84) Mbps

• THIS MULTIPLICITY RULE DOES NOT APPLY IN THE DS-N WORLD – TO CREATE THE HIGHER ELECTRICAL RATES, ONE CANNOT COMBINE, IN A LINEAR FASHION THE LOWER RATE, SIGNALS

• SONET INTERLEAVES LOWER RATE SIGNALS TO CREATE HIGHER RATE SIGNALS WITH THE NEW FRAMESTRUCTURE BEING THE BYTE-INTERLEAVED LOWERFRAME RATES

SONET/SDH BENEFITS

FOR EXAMPLE:

OC-3 = 155.52 Mbps

OC-9 GIVES (9/3 = 3 3 x 155.52 Mbps = 466.56 Mbps)



SONET/SDH BENEFITS

• SONET IS DESIGNED TO INTERFACE TO ANY EXISTINGDIGITAL SIGNALS AS WELL AS ANY FUTURE ONES SOALLOWING FOR EASE OF CURRENT AND FUTUREMIGRATION

• SONET IS DESIGNED TO SIMPLIFY THE NETWORK (LESSNUMBER OF EQUIPMENT NEEDS – BECAUSE OF THELINEAR RELATIONSHIP OF FRAMES GOING UPWARD INTOTHE HIERARCHY)

• AS A RESULT, SONET ALLOWS FOR SIMPLER NETWORKMANAGEMENT

SONET

SONET MULTIPLEXEREQUIPMENT

T3 - 44736 Mbits/s

E1 = 2.048 Mbits/

T1 = 1.544 Mbits/s

Fiber Optic Cable

SourceMultiplexer

Repeater

DestinationMultiplexer

Non-SONET

Non-SONET

section

line

path

Figure 2.49: (a) SONET allows data streams of differentformats to be combined int a single high speed fiber

optical data stream. (b) A SONET path

(a)

(b)

E1 IS THEEUROPEAN T1(32 8-BITA-LAW PCMCHANNELS PERFRAME + 1 F-BITPER FRAME)

SONET TERMINOLOGY

• THE END-TO-END CONNECTION THROUGH A SONET/SDH NETWORK IS ALWAYS CALLED THE “PATH”

• THE CONNECTION BETWEEN MAJOR NODES, SUCH AS MULTIPLEXERS (ADD/DROP MULTIPLEXERS, SONET MULTIPLEXERS) IS CALLED A “LINE”

• THE LINK BETWEEN AN ADD/DROP MULTIPLEXER (ADM) AND A REGENERATOR (REPEATER), OR BETWEEN TWO REGENERATORS, IS CALLED A “SECTION”

SONET TERMINOLOGY

SONETMUX

SONETMUX

SONET LAYER STRUCTURE

• SONET USES A LAYERED ARCHITECTURE TO DESCRIBEITS OPERATION

• PHYSICAL LAYER LOWEST LAYER

• SECTION LAYER

• LINE LAYER

• PATH LAYER HIGHEST LAYER

PHYSICAL LAYER

• THE PHYSICAL LAYER DEALS WITH THE TRANSPORT OF SONET INFORMATION ACROSS THE PHYSICAL MEDIUM

• THE LAYER IS RESPONSIBLE FOR CONVERTING ELECTRICAL STS-N SIGNALS TO OC-N OPTICAL SIGNAL AND VICE VERSA

• THE LAYER DOES NOT ADD ANY OVERHEAD TO THE SONET SIGNAL

SECTION LAYER

• THE SECTION LAYER PROVIDES FRAMING AND MAINTENANCE FUNCTION BETWEEN TWO PIECESOF SECTION TERMINATING EQUIPMENT (STE)

• THIS SECTION IS THE SMALLEST PORTION OF THE END-TO-END SONET CONNECTION, AND GENERALLYREFERS TO THE LINKS BETWEEN REGENERATORS

• THE SECTION LAYER HAS ITS OWN OVERHEAD INTHE SONET SIGNAL (SONET FRAME STRUCTURE)

LINE LAYER

• THE LINE LAYER DEALS WITH THE COMMUNICATIONSBETWEEN SONET LINE TERMINATING EQUIPMENT(LTE)

• THE LTE FUNCTIONS INCLUDE MULTIPLEXING ASWELL AS LINE MAINTENANCE AND PROTECTION

• THE LINE LAYER ALSO HAS ITS OWN OVERHEAD INTHE SONET SIGNAL (SONET FRAME STRUCTURE)

PATH LAYER

• THE PATH LAYER DEALS WITH COMMUNICATIONSBETWEEN PATH TERMINATING EQUIPMENT (PTE).

• PTE MAPS VARIOUS TYPES OF TRAFFIC INTO SONETFRAMES FOR TRANSPORT, AND REMOVES THATTRAFFIC FROM THE SONET FRAME AT THE OTHEREND OF THE PATH

• THE PATH LAYER ALSO HAS ITS OWN OVERHEAD IN THE SONET SIGNAL.

• EACH PIECE OF SONET EQUIPMENT PROCESSES ITSASSOCIATED OVERHEAD LAYER.

• PTE PROCESSES PATH OVERHEAD• LTE PROCESSES LINE OVERHEAD• STE PROCESSES SECTION OVERHEAD

• THIS LAYERED STRUCTURE LETS US DEFINE SPECIFIC FUNCTIONS FOR EACH PART OF THE SONET OVERHEAD,SO IF WE NEED TO CHANGE THAT FUNCTIONALITY, WE ONLY HAVE TO CHANGE ONE PART OF THEOVERHEAD (MODULAR DESIGN)


• ALTHOUGH EACH SONET OVERHEAD IS SEGREGATEDBY LAYERS, EACH LAYER REQUIRES THE SERVICESOF ALL THE LAYERS BELOW IT TO PERFORM ITSFUNCTIONS. SO BEFORE A PTE PROCESSES ITSOVERHEAD, THE SECTION AND LINE OVERHEAD MUSTBE PROCESSED • PROCESSING MAY BE ACCOMPLISHED BY SEPARATELTE, STE, AND PTE OR A SINGLE PIECE OF EQUIPMENT,SUCH AS A SONET MULTIPLEXER


• A SONET MULTIPLEXER IS A PTE AND OPERATES AT ALL4 SONET LAYERS (TAKES DS-3/E1/ATM CELLS IN ANDPUTS OUT AN OC-N SIGNAL OUT)

• SONET MULTIPLEXER IS ALSO CALLED A TERMINALMULTIPLEXER, OC MULTIPLEXER, BYTE INTER-LEAVEDMULTIPLEXER

• THE ADD/DROP MULTIPLEXER (ADM) IS AN LTE


SONET MULTIPLEXER

ATMDS3E1

ATMDS3E1

ADD/DROPMUX

ADD/DROPMUX

DS3DROP

DS3ADD DS3

DROP

DS3ADD

• THE ADD/DROP MULTIPLEXERS (ADMS) ARE LTE

• HOWEVER SINCE ADMS CAN ADD OR DROP SIGNALS,THEY SERVE TWO PURPOSES:

1. FROM THE PERSPECTIVE OF THE TRAFFIC JUST PASSING THROUGH HERE, THESE ADMS ARE FUNCTIONING AS LTE

2. BUT FOR THE DS3 THAT IS DROPPED AND FOR THE ONE THAT IS ADDED, THESE ADMS ARE PTE

SONET MULTIPLEXER


SONETMUX ADM REPEATER

telecommunications systems and technology part 4-1

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