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)
A COMMUNICATIONS LINK
WHEN DATA IS TRANSMITTED OVER A
COMMUNICATIONS MEDIUM, VARIOUS TASKS
MUST BE PROVIDED ON THE LINK (THIS IS THE
DIFFERENCE BETWEEN A DUMB WIRE/GLASS AND AN
INTELLIGENT WIRE/GLASS – LINK)
THESE INCLUDE:
1.
FRAMING OF THE DATA
2.
ERROR CHECKING
3.
LINK MANAGEMENT
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
USEFUL LINKS
ANSI HOME PAGE:
http://www.ansi.org/
ITU HOME PAGE:
http://www.itu.int/home/index.html
ITU TELECOM PAGE:
http://www.itu.int/ITU-T/
SONET Vs SDH
• THERE ARE A LOT OF SIMILARITIES BETWEEN
SONET AND SDH, THERE ARE SOME SIGNIFICANT
DIFFERENCES, ESPECIALLY IN TERMINOLOGY.
• SONET IS A SUBSET OF SDH AND IT IS EASIER TO
INTRODUCE THE TOPIC FROM A SONET POINT OF VIEW
AS UNDERSTANDING SONET MAKES IT EASIER TO
UNDERSTAND SDH
• FOR EXAMPLE CERTAIN ASPECTS OF SDH EXIST TO
MAINTAIN COMPATIBILITY WITH SONET
HISTORY
1. PRE-1960’S
INDIVIDUAL ANALOG LINES BETWEEN
SWITCHING OFFICES
HISTORY
2. 1962
AT&T DS-1 T1-CARRIER DIGITAL SERVICE
CHANNEL BANK RESIDES IN C.O.
HISTORY
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’S
• 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
Multiplexer
Multiplexer
Two optical fibers
(Tx and Rx)
MULTPLEXER RESIDES IN C.O.
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
HISTORY
• STANDARDS IN OPTICAL COMMUNICATIONS
BECAME APPARENT
• 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
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
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 DS1’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
OC-3
OC-9
51.84
155.52
466.56
28
84
252
1
3
9
OC-12
OC-18
OC-24
OC-36
622.08
933.12
1244.16
1866.24
336
504
672
1008
12
18
24
36
OC-48
2488.32
1344
48
SONET MUX RATES
OC-1
LABEL
Mbps
OC-96
OC-192
4976.64
9953.28
OC-255
13920.0
EQUIVALENT
DS1
DS3
2688
96
5376
192
6120
255
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 FURTHER
WITHOUT REPEATER THAN ELECTRICAL SIGNALS CAN
OVER COPPER
• WHILE A DS-3 CIRCUIT NEEDS A REPEATER EVERY
450 FEET, A SONET CIRCUIT WILL NEED A REPEATER
AFTER 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 OF
THE OC-1 DATA RATE.
OC-N STRUCTURE  OC-N = (N x 51.84) Mbps
• THIS MULTIPLICITY RULE DOES NOT APPLY IN THE DSN 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 FRAME
STRUCTURE BEING THE BYTE-INTERLEAVED LOWER
FRAME 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)
OC-12 GIVES (12/3 = 4  4 x 155.52 Mbps = 622.08 Mbps)
OC-192 GIVES (192/3 = 64  64 x 155.52 Mbps = 9953.28 Mbps)
SONET/SDH BENEFITS
• SONET IS DESIGNED TO INTERFACE TO ANY EXISTING
DIGITAL SIGNALS AS WELL AS ANY FUTURE ONES SO
ALLOWING FOR EASE OF CURRENT AND FUTURE
MIGRATION
• SONET IS DESIGNED TO SIMPLIFY THE NETWORK (LESS
NUMBER OF EQUIPMENT NEEDS – BECAUSE OF THE
LINEAR RELATIONSHIP OF FRAMES GOING UPWARD INTO
THE HIERARCHY)
• AS A RESULT, SONET ALLOWS FOR SIMPLER NETWORK
MANAGEMENT
SONET
E1 IS THE
T3 - 44736 Mbits/s
EUROPEAN T1
E1 = 2.048 Mbits/
(32 8-BIT
A-LAW PCM
CHANNELS PER T1 = 1.544 Mbits/s
FRAME + 1 F-BIT
PER FRAME) NonSONET
SONET MULTIPLEXER
EQUIPMENT
Fiber Optic Cable
(a)
NonSONET
Repeater
Source
Multiplexer
Destination
Multiplexer
section
line
path
(b)
Figure 2.49: (a) SONET allows data streams of different
formats to be combined int a single high speed fiber
optical data stream. (b) A SONET path
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
SONET
MUX
SONET
MUX
SONET LAYER STRUCTURE
• SONET USES A LAYERED ARCHITECTURE TO DESCRIBE
ITS OPERATION
• PHYSICAL LAYER  LOWEST LAYER
• SECTION LAYER
• LINE LAYER
• PATH LAYER  HIGHEST LAYER
SONET LAYER STRUCTURE
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 PIECES
OF SECTION TERMINATING EQUIPMENT (STE)
• THIS SECTION IS THE SMALLEST PORTION OF THE
END-TO-END SONET CONNECTION, AND GENERALLY
REFERS TO THE LINKS BETWEEN REGENERATORS
• THE SECTION LAYER HAS ITS OWN OVERHEAD IN
THE SONET SIGNAL (SONET FRAME STRUCTURE)
LINE LAYER
• THE LINE LAYER DEALS WITH THE COMMUNICATIONS
BETWEEN SONET LINE TERMINATING EQUIPMENT
(LTE)
• THE LTE FUNCTIONS INCLUDE MULTIPLEXING AS
WELL AS LINE MAINTENANCE AND PROTECTION
• THE LINE LAYER ALSO HAS ITS OWN OVERHEAD IN
THE SONET SIGNAL (SONET FRAME STRUCTURE)
PATH LAYER
• THE PATH LAYER DEALS WITH COMMUNICATIONS
BETWEEN PATH TERMINATING EQUIPMENT (PTE).
• PTE MAPS VARIOUS TYPES OF TRAFFIC INTO SONET
FRAMES FOR TRANSPORT, AND REMOVES THAT
TRAFFIC FROM THE SONET FRAME AT THE OTHER
END OF THE PATH
• THE PATH LAYER ALSO HAS ITS OWN OVERHEAD
IN THE SONET SIGNAL.
SONET LAYER STRUCTURE
• EACH PIECE OF SONET EQUIPMENT PROCESSES ITS
ASSOCIATED 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 THE
OVERHEAD (MODULAR DESIGN)
SONET LAYER STRUCTURE
• ALTHOUGH EACH SONET OVERHEAD IS SEGREGATED
BY LAYERS, EACH LAYER REQUIRES THE SERVICES
OF ALL THE LAYERS BELOW IT TO PERFORM ITS
FUNCTIONS. SO BEFORE A PTE PROCESSES ITS
OVERHEAD, THE SECTION AND LINE OVERHEAD MUST
BE PROCESSED
• PROCESSING MAY BE ACCOMPLISHED BY SEPARATE
LTE, STE, AND PTE OR A SINGLE PIECE OF EQUIPMENT,
SUCH AS A SONET MULTIPLEXER
SONET LAYER STRUCTURE
• A SONET MULTIPLEXER IS A PTE AND OPERATES AT ALL
4 SONET LAYERS (TAKES DS-3/E1/ATM CELLS IN AND
PUTS OUT AN OC-N SIGNAL OUT)
• SONET MULTIPLEXER IS ALSO CALLED A TERMINAL
MULTIPLEXER, OC MULTIPLEXER, BYTE INTER-LEAVED
MULTIPLEXER
• THE ADD/DROP MULTIPLEXER (ADM) IS AN LTE
SONET MULTIPLEXER
ATM
DS3
E1
DS3
DS3
DROP ADD
ADD/DROP
MUX
DS3
ADD
DS3
DROP
ATM
DS3
E1
ADD/DROP
MUX
SONET MULTIPLEXER
•
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 LAYER STRUCTURE
SONET
MUX
ADM
REPEATER