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) S YNCHRONOUS D IGITAL H IERARCHY ( CCITT  ITU)

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 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

USEFUL LINKS 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 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

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’S HISTORY 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 ( MBPS) SIGNALS. THE EUROPEANS NEEDED A SPECIFICATION WHICH WOULD CARRY E1 (2.048 MBPS), E3 ( MBPS), AND 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 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 Mbps WITH SONET THE RATE STARTS AT Mbps

SONET MUX RATES LABELMbpsEQUIVALENT DS1DS3 OC OC OC OC OC OC OC OC

SONET MUX RATES LABELMbpsEQUIVALENT DS1DS3 OC OC OC 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 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 ) IS MUCH LOWER THAN THAT OF ELECTRICAL SIGNALS OVER COPPER (BER = 1 X )

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 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 FRAME STRUCTURE BEING THE BYTE-INTERLEAVED LOWER FRAME RATES

SONET/SDH BENEFITS FOR EXAMPLE: OC-3 = Mbps OC-9 GIVES (9/3 = 3  3 x Mbps = Mbps) OC-12 GIVES (12/3 = 4  4 x Mbps = Mbps) OC-192 GIVES (192/3 = 64  64 x Mbps = 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 EUROPEAN T1 (32 8-BIT A-LAW PCM CHANNELS PER FRAME + 1 F-BIT PER 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 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.

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 LAYER STRUCTURE

SONET MULTIPLEXER ATM DS3 E1 ATM DS3 E1 ADD/DROP MUX ADD/DROP MUX DS3 DROP DS3 ADD DS3 DROP DS3 ADD

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

SONET LAYER STRUCTURE SONET MUX ADMREPEATER