payload 4(part1)

8/7/2019 Payload 4(Part1)

http://slidepdf.com/reader/full/payload-4part1 1/100

Chapter 5: SONET/SDH

Reference textbook:³Understanding SONET/SDH and ATM:Communications Networks for The Next

Millennium´ By S1. V. Kartalopoulos



Introduction

³Humans are social animals!´Socializing exchanging ideas and information buildnetworks to facilitate information exchange andcommunication

Different ways of communication technologieso Telegrapho Telephonyo Digital electronic technology of various data types

Telemetry data

User dataVideo dataVoice data



F ig. 5.1 Characteristics per service



5.1 Legacy Communications Systems:

Concepts

Basic Technology and Services



P ulse-Coded Modulation ( P CM )

Voice : the primary services in the communication industryo Voice : analog signal.o Words : acoustic waves generated by vibrating vocal cords and the

mouth cavity modulates them into recognizable and distinguishablecompounded sounds

o Microphone: a transducer converts acoustic waves into (analog)electrical signalso Speaker: a transducer converts (analog) electrical signals into

acoustic waves and reproduces voice soundsP OTS ( P lain Old Telephone Service )

o Ringingo call initiationo number dialingo Transmits analog signals over the telephone network




P CM form a binary (or digital) bit stream at 64000 bits/secondAlso know as Digital S ignal level 0 ( DS0 )(en)Coder : converts analog signal into digital bit steamsDecoder : converts digital bit streams into analog signal (voices)CODEC ( coder/decoder ) : periodically samples the analog signal, and basedon a conversion scheme, it translates each sampled value into a binaryrepresentationTwo major schemes for P CM : -law in United States, -low in EuropeAcoustical signal of speaking voice : usually under 3.4 kilocycles per second,or kilohertz ( 3.4 kHz )A low-pass filter removes all components of frequency higher than 3.4 kHzBy sampling theorem, to truly represent a signal, we must sample at least

twice as its maximum frequency contentSo P CM CODEC samples at analog voices 8000 times per second, or every125 ms, and it converts each sample into 8 bits P CMThe total bit rate is 8000 × 8 = 64000 bits / second, or 64 kilobits per second (64 Kbps ), this is the rate termed DS0.



F ig. 5.2 Analog to P CM



F ig. 5.3 DS0 rate




Differential P CM ( D P CM ) , adaptive D P CM ( AD P CM ),and sigma-delta P CM ( P CM ) : by more sophisticateddigital signal processing algorithms to compress the 64Kbps to 32 Kbps, or 16 Kbps, or even lower than that.

Local loop : a pair of twisted copper wires between user¶sequipment ( a P OTS telephone ) and the serviceprovider¶s equipment, where the CODEC is located. Thesignal transmitted on a local loop cable is an analogelectrical signal.



Time-Division Multiplexing ( TDM )

P OTS telephone converts voice signals into an electricalsignalThe electrical signal is sent over a pair of copper wires toa communications systems where the CODEC function is

performedThe backbone network only transmits digital signals andno analog signals : all-digital communications networkOn an all-digital communications network, in addition todigitized voice signals, other digital data can also betransmitted ( raw digital data, encoded video, encodedsound, etc. )




Some digital services on DS0o Digital Data Service ( DDS )

56 Kbps for data, 8 Kbps for ³in-band´ signalingOnly for the backbone network, not for the end users

o Basic Rate Integrated Services Digital Network ( BR ISDN or BR I )Uses two 64 Kbps channels ( channels B ) and a 16 Kbps subratechannel ( channel D )Support a combination of voice and/or data services over a single pair of wireModes available for end users :

2 B channels for voice and a D channel for data1 B channel for voice and a B+D channels for data

2 B channels for data and a D channel for signaling All channels for dataCan only be used if both end users has ISDN and the network supportsISDN



Abbreviations :CCC, clear channel capability;B = 64 Kbps voice or data channel;DDS, digital data services;D = 16 Kbps signaling or data channel

B8ZSB channel ( 2B + D )

64 CCCB-ISDN 64 Kbps

64 CCCB8ZS

DDS 56 Kbps + 8 Kbps signalling

F rame, bit robbedVoice : 64 Kbps

F ormat, overheadline code

Source

Table 5.1 DS0 Rates and Line Codes




User-to-network interface ( UN I ) : the interface where theuser signal, a 64 Kbps data stream ( organized in 8-bitbytes ), first meets the networkAt UNI, users¶ signals are synchronized with a 8 kHz

system clock, or a multiple of it.Then based on a round-robin principle, the signals aresequentially polled one byte at a time and place one after the other in a fixed order, this is called byte-interleaving.Time slot : the location of each byte source in this ordereddigital signal.The whole process is called Time-Division Multiplexing (TDM ).



DS1 Rate

Multiplex 24 DS0 usersEach user contributes one byte in a DS1 frameAn additional bit, the F -bit, is used as the beginning of a DS1frameTotal 24 × 8 + 1 = 193 bits in 125 s.The bit rate is 193 bits / 125 ms = 1.544 Mbps, knows as thedigital signal level 1 ( DS1 ) rate.M1 multiplexer ( M1 mux ) : function that TDM 24 DS0 into aDS1.The F -bit of each frame forms an F subrate channel in DS1

superframeo 12 or 24 frames in each super frameo P rovide a data link over which the network data are sento P rovide error control



F ig. 5.4 DS1 rate ± M1 Mux



DS1 F ormats

DS1 frame = 24 time slots and the F -bitF or primary rate ISDN ( P R I )

o 23 time slots : 23 B channels ( at 64 Kbps each )o 1 time slot : for 4 D channels

DS 1 signalo Alternate mark inversion ( AM I ), or called bipolar with

8-zero substitution, a.k.a. bits 8-zero suppression (B8ZS )

o B8ZS or more generally, BnZS is used to prevent

transmit long strings of 0¶s by the minimum number of 1¶s



Table 5.2 DS1 Rate and Line Codes

Abbreviations : S F , superframe; ES F , extended superframe; AM I, alternatemark inversion.

AMIB channel ( 2B + D )

S F , ES FP -ISDN 23B + D

S F , ES F , B8ZSDDS 23 × DS0 + sync + frame

S F , ES F , AMIVoice : 24 × DS0

F ormat, Overhead Line CodeSource



DS1 Over Long Distnace

DS1 signal is transmitted over a T1 lineo One pair of wires is used for each directionCommunication systems at the DS1 level are designedwith an error rate of 10 -6 or better.

A regenerator is placed after 3000 ft from user and every6000 ft between regenerators.A regenerator every 6000 ft places a maintenance andtroubleshooting overhead.



F ig. 5.5 T1 characteristics



xDSL

Digital Subscriber Line ( DSL ) : the local loop ( i.e. thecopper twister-pair wires between most homes and thetelephone service provider equipment ) in digital form,such as the BR I.

DSL provides 1.544 Mbps and in some cases up to 7Mbps over existing twisted-pair copper cable.DSL cannot be used on ³loaded´ loops, i.e., no inductorsor coils on the loop cable.Effective distance of a DSL depends on the data rate

supportedo 1.5 Mbps : several mileso 25 Mbps : only half a milexDSL : ³x´ refers to one of many DSL formats and rates.



xDSL

VDSL : very high-bit-rate DSLHDSL : high-bit-rate DSLADSL : asymmetric DSLSDSL : symmetric DSL

RADSL : rate adaptive DSLMSDSL : multi-rate symmetric DSLo Build on a single pair of DSL technologyo On unloaded copper pair, can provide 64/128 Kbps up

to 8.9 Km, or 2 Mbps up to 4.5 Km

DSL requires terminating devices at both ends of theloop, at the user and at the service provider, to terminatethe upstream and downstream digital signals.



Modulations on DSL

Two-bits-to-one quaternary ( 2B1Q ) : Digital P AM with -3, -1, +1 and+3, four possible levels, each represents 2 bits.

o Its transmitted power is superior to that of AM I

o Bit rate is limited to 392 Kbpso Suitable for upstream transmission on local looso

This is used for BRI

signals.Discrete multi-tone ( DMT ) : divides the bandwidth into frequencychannels.

o When a certain channel is detected to have inferior transmissioncharacteristics, the traffic is assigned another frequency channel,a.k.a. frequency hopping.

o The official standard of the ANS I T1E1.r working groupo Supports upto to 6 Mbps services

Up to four M P EG-1 compressed video data A single M P EG-2 compressed video data



Modulations on DSL

Carrierless amplitude phase ( CA P ): a derivative of thequadrature amplitude modulation ( QAM )

o Translates a 4-bit code in one of the 16 voltage phasepoints

o May be viewed as a 2B1Q 2-dimensional approach.o Transmitting power is superior to that of AM I and 2B1Qo Effective bit rate is in the range of 10 ± 175 Kbpso The de facto standard that by 1996 was deployed in

almost 97% of all ADSL applications.



Table 5.3 Various Modulations on DSLs

180006415001 ADSL CA P

1200064060001 ADSL CA P

1200017615001 ADSL DMT

120007687681HDSLSingle pair

13000204820482HDSLTwo pairs

180001441442ISDN

Max. length inone loop( in ft )

Upstream bitrate in Kbps

Downstream bitrate in Kbps

# of wires inpairs

Modulations



LVDS

Low-Voltage Differential Signaling ( LVDS )Once defined for high-speed data transmission over relatively long cablesNow used as a high speed, 155.5 Mbps, low-power

general purpose data transmission technology at theboard / bus levelsLVDS differential voltage swing is between the voltagelevels V OH = 1.4 V, and V OL = 1.0 VScalable Coherent Interface LVDS ( SC I-LVDS )o Specified by the IEEE 1596.3 standardo F or unidirectional point-to-point links, from a transmitter

to a receiver



1000BaseT

An evolutionary standard derived from the 100BaseTused in LANs.Working on by the IEEE 802.3ab task force.Allows for transmission of a balanced digital signal at 1

Gbps over UT P -5 cable for the distance of 100 m.Most of the applications are in the LAN



Coding Schemes

Unipolar : a two-voltage-level signal that typically swingsbetween zero voltage and + V.Bipolar : a three-voltage-level signal that typically swingsbetween a positive and a negative voltage

o May return to zero ( RZ ) or nonreturn to zero ( NRZ )o In a digital bipolar signal, the 1¶s alternate between the

two voltages, ³+´ and ³-´ and this will result in a zeroDC component on the transmission line.

A unipolar and a NRZ bipolar are considered as on-off

signalso May applied to either electrical or optical signalsMulti-level signal : several voltage levels are use



F ig. 5.6 Unipolar and bipolar coding



Coding Schemes

RN and NRZo F or both methods, the signal alternates between a

positive ( +V ) and a negative ( -V ) voltageo Logic ³1´ : positive voltageo Logic ³0´ : negative voltageo F or NRZ, transitions between logic ³0´ and logic ³1´,

and vice versa, are directly crossing the zero voltagelevel

o F or RZ : transitions between logic ³0´ and logic ³1´, and

vice versa, stay temporarily on the zero voltage level



F ig. 5.7 RZ and NRZ coding



Coding Schemes

4B/5B coding : translates 4 bits into one of the 16 predetermined 5-bitcodes.

o The original 4-bit code 0000 is translated to a 5-bit not-all-zerocode.

Bipolar Violations ( BV )o

Bipolar signal is a 3-level signal where consecutive 1¶s in the bitstream are alternating polarityo BV is when two consecutive µ1s do not change polarityo Can be used to detect errors in the bit streamo Or used to mark a specific bit manipulation ( coding ) in the bit

stream

B8ZS ( bit 8-zero suppression ) : find 8 consecutive 0¶s in the bitstream and substitutes them with a bipolar violationo At the receiver, BV is detected and the bit stream is restored to its

original formHDB3 : substitueds four 0¶s by a code that contains a violation.

o At the receiver, BV is detected and the bit stream is restored to its

original form



F ig. 5.8 Bipolar and bipolar violation



5.1 Legacy Communications Systems:Concepts

Hierarchical Multiplexing



Multiplexing in North America

24 DS0 signals + a framing F -bit level 1 multiplexer (M1 ) a DS1 signal4 DS1 signals + a control C-bit ( for every 48 payload bits) bit interleaved by a level 1-to-2 multiplexer ( M12 ) a

DS2 signal7 DS2 signals + a control C-bit ( for every 84 payload bits) bit interleaved by a level 2-to-3 multiplexer ( M23 ) aDS3 signalTwo-stage multiplexing : multiplexing from DS1 to DS3

DS2, although defined, are seldom used. Instead, an M13multiplexer is used that multiplexes in one-stage 28 DS1signals and all the F -bits, C-bits into a DS3 signal with bitrate of 44.736 Mbps.



F ig. 5.9 T-carrier hierarchy



Stuffing Bits

A DS2 signal is formed by bit interleaving 4 DS1 signalso In a recurrent manner, a bit from each of the 4 DS1¶s is

placed ina sequential order But the four DS1 signal sources may be a slightly different

bit rage then the expected 1.544 MbpsStuffing additional bits in specfic time slots of slower DS1signal so that the composite DS2 signal is exactly 6.183MbpsStuffing bits are also used when 7 DS2 signals are

multiplexing into a DS3 signals



F ig. 5.10 DS2 frame ( 6.312 Mbps ) withBit Stuffing



F ig. 5.11 DS3 frame ( 44.736 Mbps ) withBit Stuffing



T1c Rate

Another legacy system format.2 DS1 signals and a control bit ( C-bit ) a M11c bit-interleaved multiplexer a DS1c signalDS1c signal uses a duo-binary modulation and in effect

doubles the bandwidth capacity of a T1 line



F ig. 5.12 T-carrier hierarchy



Multiplexing in Europe

European systems time-division multiplex 30 user time slots andone ( framing and signaling ) time slot for every 15 user timeslots to yield an E1 ( or E11 ) frame with 32 time slots.The functions of the multiplexer are round-robin polling, byteinterleaving, and time compression.In the receiving end, an E1 signal is demultiplexed into 30 user channels and 2 added channels for framing and signaling andeach channel is decompressed to 64 Kbps.Each frame is transmitted within 125 s, so the total bit rate is2.048 Mbps.

E1 is different from DS1 in bit rate and also the absence of theF

-bit.E1 signal uses an alternate mark inversion ( AM I ) with a high-density bipolar three-zero ( HDB3 ) techniques.



F ig. 5.13 E1 rate ( 2.048 Mbps )



Multiplexing in Europe

30 DS0 channels + 2 64-Kbps channels ( for framing andsignaling ) time compressed and byte multiplexed by alevel 1 multiplexer an E1 signal4 E1 signals + 4 64-Kbps channels ( for signaling ) time

compressed and bit interleaved by a level 1-to-2multiplexer an E2 signal ( 8.448 Mbps ).4 E2 signals + 9 64-Kbps channels ( for signaling ) timecompressed and bit interleaved by a level 2-to-3multiplexer an E3 signal ( 34.368 Mbps ).



F ig. 5.14 European hierarchy



Table 5.4 Legacy Rates

397.2 Mbps

274.176 MbpsDS4

139.264 MbpsE397.728 Mbps

91.053 MbpsDS3c

34.368 Mbps44.736 MbpsDS3

32.064 Mbps8.448 MbpsE2

6.312 Mbps6.312 MbpsDS2

3.152 Mbps3.152 MbpsDS1c

2.048 Mbps-E1

1.544 Mbps-1.544 MbpsDS1

64 Kbps64 Kbps64 KbpsDS0

JapanEuropeUnited StatesF acility



P ROS and CONS of Legacy Networks

Legacy networks were initially designed to carry voicesignal from many sources to many destinations.Switching functions play very important role in the legacynetworks.

Due to the circuit-switching nature, time slots areassigned to a particular user for as long as the connectionis alive, therefore the system is deterministic and itsdesign simpler.P re-assigned time slots uses bandwidth inefficiently

So, legacy networks do not cost-effectively accommodatehigh-bit-rate services



5.1 Legacy Communications Systems:Concepts

Legacy Data Networks



Legacy Data Networks

Legacy synchronous communications networks do not address therequirements for voice and data applications in an equitable manner.F or voice communications, short delays through the network were theprimary concern.F or data applications, the major concerns are high bit rates and lowcost per unit of time.

o F or example, banks, stock-brokerage firms, publishing companies,image transmission.

o Data will be transferred in chunks, up to about 9000 bytes, knownas packets.

o Such systems are local area network ( LAN ), metropolitan area

network ( MAN ), wide area network ( WAN ), and the switchedmultimegabit data services ( SMDS ).



LAN

Networks for a limited area ( building, campus ).Many terminals were connected on a LAN backbone, andbased on a LAN communications protocol, terminals wereable to communicate among them.

Two major types : Ethernet and ring.Ethernet LANs ( IEEE 802.1 ) : hierarchical andtransmission rates is at 10 or 100 Mbps.

o Ethernet 10BaseT : 10 Mbps over a twisted pair of wires

F DD I ( F iber Distributed Data Interface ) ( IEEE 802.5 ) : acounter-rotating fiber ring LAN at 100 Mbps effective datarate.

o F DD I employs 4B/5B coding and thus the actual bitrate is 125 Mbps.



MAN

LANs were expanded to cover a city or a metropolis andthe MAN is evolvedTraffic from one LAN was brought to another via afunction known as bridge.

LAN/MAN traffic was routed on the communicationsnetworks so that connectivity between 2 or more remoteLANs/MANs could be established.Dedicated links can be deployed if high traffics betweentwo LANs/MANs is sustained 24 hours a day.



SMDS

A public MAN service developed by BellcoreP rimarily for LAN interconnections.Based on the distributed queue dual bus ( DQDB)transport and multiplexing mechanism and is defined inIEEE 802.6.The use of the DQDB format is based on a 53-byte cell

structure that is similar to the ATM cell.SMDS is a connectionless technology specified over synchronous carriers like DS1, DS3, E1 and E3 lines.



F rame Relay ( F R )

F R is a packet service.Design philosophy is similar to that of a highway withramps on and off.

o At the ramps, any car, small or large, may approach

the highway at a slower speed.o Once on the highway, one can travel any length of thehighway and as fast as the limit.

o So highway is equally accessible and shareable by all.In F R, the ramps are the access points and the number of

lances determines the bandwidth of the F R system.o F R is a shared-bandwidth solution that takes

advantage of traffic pattern variability andoversubscription to provide a cost-effective dataservice.



F rame Relay ( F R )

At the access points, or the user-to-network interface,circuitry concentrates the packet traffic from a number of users, typically over leased lines ( T1 / E1 ).The concentrated traffic is switched by means of a F R

switch and it is put on a common backbone ( the highway).A number of F R switches are interconnected to form a F Rnetwork.



5.2 SONET and SDH

Introduction



Introduction

The evolution from copper wires to optical fibers led too Synchronous Optical Network ( SONET ) in USo Synchronous Digital Hierarchy ( SDH ) in Europeo Since first deployment in the 1980s, SONET / SDH

have almost replaced all long-haul copper cables.o The optical fiber has responded to an unexpectedincrease in traffic demand and make ³ informationsuperhighway ³ a reality



SONET / SDH

SONET is a set of standard interfaces in an opticalsynchronous network of elements ( NE ) that conform tothese interfaces.SONET interfaces define all layers, from the physical to

the application layer.SONET is a synchronous networkSDH is also a synchronous network with opticalinterfaces.SDH is a set of standard interfaces in a network of

elements that conform to these interfaces.Like SONET, SDH interfaces define all layers, from thephysical to the application layer.



F ig. 5. 15 SONET / SDH services



SONET versus SDH

Technical similarities between SONET and SDHo Bit rates and frame format organizationo F rame synchronization schemeso Multiplexing and de-multiplexing ruleso Error controlMajor differences :

o The variations about overhead bytes to accommodate differencesbetween US and European communications nodes and networks

o The SDH photonic interface specifies more parameters thanSONET

o SONET and SDH have enough minor technical and linguistic

differences to add complexity ( and cost ) in their design



SONET versus SDH

Some nomenclature exampleso Synchronous transport signal ( STS ) versus

synchronous transport module ( STM ), e.g., STS-1,STS-3, STS-12, STS-48 versus STM-1, STM-4, STM-

16.o Synchronous payload envelope ( S P E ) versus virtualcontainer ( VC )

o Virtual tributary ( VT ) versus tributary unit ( TU )



SONET / SDH Benefits

Reduced cost:o It lowers operations costo It has the same interface for all vendors

Integrated network elementso I

t allows for multi-vendor internetworkingo It has enhanced network element managementRemote operations capabilities : provision, test, inventory,customize, and reconfiguredIt offers network survivability features.

It is compatible with legacy and future networks



SONET and SDH Rates

SONET and SDH rates are in the range of 51.85 ±9953.28 MbpsSONET signal in electrical nature : synchronous transportsignal level N ( STM-N )

SDH signal in electrical nature : synchronous transportmodule level N ( STM-N )In optical signal nature : optical carrier level N ( OC-N )



Table 5.5 SONET / SDH Rates



Why Use SONET / SDH ?

Why is glass fiber better than copper wire ?o Higher transmission reliability.

Glass fiber is not as susceptible to radio frequency or electromagneticinterference ( R FI , EM I ) as copper wire unless it is shielded and wellgrounded

o Lower bit error rate ( BER ) : lower inter-symbol interference amongfibers than copper wires, so lower bit error rate.

o Higher bandwidth per fiber o F iber can transmit without repeaters at longer distance compared to

copper wires.o F iber yields thinner cable than copper.o SONET/SDH is based on standards, which enables multivendor

compatibility and interoperability.



F ig. 5. 16 SONET network



Network Topologies

Three major network topologies : tree, ring, and meshTreeo A hierarchical distribution of NEso Most used in LANs, such as Etherneto A source is connected to a distribution function ( known

as hub ) that routes a source packet to its destinationnode.

o A connection between source and destination isestablished for the duration of the packet through the

hub.o Very efficient for asynchronous data transmission but

not for real-time data and voice.o If a hub fails, all connections through it die.



Network Topologies

Ring : consists of NEs interconnected with a dual fiber,the primary and secondary, to form a ring.

o Some of the NEs are also assigned to communicationwith other rings or topologies

o When one fiber fails, the other can still keep theintegrity of the ring

o If both fiber breaks, then the network is reconfigured,forming a ring using both the primary and secondaryand the packets will flow through all fibers but the

broken ones.o Ring offers fast path protection and is widely used in

LANs or within a relatively limited radius ( campus,town, high risers).



Network Topologies

Mesh : consists of NEs fully interconnectedo When one link breaks, the adjacent NE detects the

breakage and reroutes the traffic to another NE.o Mesh provides transmission protection and network

restoration capabilities.o Mesh also provides disaster avoidance capabilities

when a cluster of NEs may fail.o Better applicable in densely populated areas.SONET / SDH networks are based on ring topologies

Other topologies may be mixed into networks as well.



F ig. 5. 17 Ring, tree and mesh topologies



A Hierarchical P rocess

A hierarchical process can transformed any type of non-SONET signal into SONET networks.

1. Segmenting the signal and mapping the segments insmall containers known as virtual tributaries ( VTs ).

2. Once the VTs have been filled with segmented payload,they are grouped in larger containers that are know asgroups.

3. Groups are then mapped into a SONET frame.4. Many contiguous frames entails the SONET signals to be

transmitted over the OC-N fiber.In SDH, VT are called tributary units ( TUs ) and thegroups are called tributary unit groups ( TUGs ).



F ig. 5. 18 SONET hierarchy



Table 5.6 Broadband Services and Rates

9953.280STM-64STS-192

Uncompressed HDTV2488.320STM-16STS-48

Uncompressed Extended Quality TV622.080STM-4STS-12

SMDS, broadband-ATM, high-definition TV (HDTV )

155.520STM-1STS-3

51.840STM-0STS-1

6.912VT6

3.456VT3

High-capacity digital services2.304VT2

Voice / high-speed digital services1.728VT1.5

Sample ServicesBit Rate ( Mbps)

SDHSONET



P ath, Line and Section

A SONET / SDH frame is transmitted from an end user toanother end user through nodes in the network.To ensure the deliverability and the integrity of the signal,overheads are added to the sending signal to be used for network administration purposes.This overhead information is transparent to end users.The overhead has been organized hierarchically in threetypes :

o P atho

Lineo Section



P ath, Line and Section

P ath : overhead added at transmitting path-terminating equipment (P TE ), and it is read by the receiving P TE.

o P ath information is not checked or altered by intermediateequipment

Line : overhead added by the transmitting line-terminating equipment (LTE ) to be used by the receiving LTE.

o At the edges of the networks, ( where there are no LTEs, ) P TEsplay the role of LTEs

Section : overhead added by equipment terminating a physicalsegment of the transmission facility.

o A segment between two repeaterso A segment between an LTE and a repeater o A segment between an P TE and a repeater o A segment between two adjacent LTEs where no repeaters

between them.o All these are sections.



F ig. 5.19 P ath/Line/Section definitions



F ig. 5.20 P ath/Line/Section definitions



5.2 SONET and SDH

SONET/SDH F rames



STS-1

The smallest SONET frameCan be visualized as a 2-dimensional matrix of 9 rows by90 columns, each entry is a byte.The whole STS-1 has 9 x 90 = 810 bytesThe first 3 columns : transport overhead for section andline.Synchronous P ayload Envelope ( S P E ) : the bytecapacity contained from the 4 th column to the last column,totally 87 columns or 783 bytes.P

ath overhead : the 4th

column.F ixed stuff : columns 30 and 59 of the STS-1.The actual payload capacity is 84 columns, i.e., 756 bytesor 48.384 Mbps effective bit rate.



F ig. 5.21 SONET STS-1 frame structure



SDH AU-3

SDH does not specify a frame similar to SONET STS-1.It has a payload container as small as the SONET S P E,know as virtual container 3 ( VC-3 ).VC-3 has a column for path overhead, called the VC-3path overhead ( VC-3 P OH ), and two fixed stuff columns( columns 30, 59 of VC-3 ).The actual payload capacity in a VC-3 is also 84 columnsor 756 bytes, similar to the SONET case.At the VC-3 and in the 4 th row, three additional bytes are

added for the VC-3 pointer ( H1, H2, and H3 ).Administrative unit level 3 ( AU-3 ) : VC-3 + VC-3 pointer AUG ( administrative unit group ) : 3 AU-3s are byte-multiplexed

f



F ig. 5.22 SDH AU-3 frame structure



Transmitting an STS-1

To transmit an STS-1 over optical fibers, one starts withthe most significant bit ( MSB ) of the byte in column 1,row 1.Then when the byte is serially transmitted, it continueswith the byte in column 2, row 1; and so on.After the first row is transmitted, the process will transmitthe 2 nd row, and so on.In 125 s, all 6480 bits are transmitted, so the bit rate is51.86 Mbps.

F i 5 23 SONET STS 1 f f ld d



F ig. 5.23 SONET STS-1 frame: unfolded

F l i F



F loating F rames

SP E = user data + path overheadSTS-1 = S P E + line and section overheadWhen an STS-1 is received, the beginning of the frame isnot necessary synchronous with the beginning of theframe that the receiving node generates.The receiving node may need additional time to processthe overhead information.If the S P E waits for receiving node to synchronized, willsuffer added delays, which is bad for a high-speed

transmission network.So , the ³floating´ S P E technique is used to minimizeddelays.

F i 5 24 STS 1 f S P E f ld d



F ig. 5.24 STS-1 frame ± S P E unfolded

F l i F



F loating F rames

The process of an S P E is separated from the process of the line and section overhead of an STS-1.The received S P E may be out of phase ( in increments of bytes ) with the beginning of the STS-1 frame, which is insynchronization with the NE.This ³out of phase´ can be viewed as an offset in theSTS-1 frame, in terms of columns and rows.Thus, the first byte of the receiving S P E ( this will be thefirst byte of the path overhead ) is mapped in the S P E of

the current STS-1 frame on row N and column K, for example.As more bytes are received, the received S P E is wrappedaround the STS-1 S P E space.

F l ti F



F loating F rames

Resulting path overhead will be aligned in the K th column.Due to the offset, not all bytes of the received S P E will beable to fit in the S P E space of the current STS-1 frame.And the rest of the S P E will be mapped to the next STS-1S P E and each S P E are synchronous with the 125- sinterval.The end result will be an S P E mapped over twoconsecutive frames.

SONET STS 1 ith fl ti S



SONET STS-1 with floating S

Mapping a floating ( partial ) S P E in an



pp g g ( p )STS-1 frame

Mapping a floating ( complete ) S P E in



pp g g ( p )STS-1

Section Overhead : SONET



Section Overhead : SONET

The first 3 rows of the overhead space in an STS-1 frame, totally 9bytes, carry synchronization and section overhead information.A1 and A2 are fixed patterns : 0x F 628 or in binary 1111 0110 00101000. Receiver will use these to detect the beginning of the frame.

o A1, A2 are not scrambled.C1 : STS-1 ID, defined for each STS-1.B1 : used for error monitoring.E1 : a 64-Kbps voice communication channel for craft personnel.

o In an STS-N signal, E1 is defined for the 1 st STS-1 only. The other N-1 E1¶s are not used.

F 1 : used by the section.D1 to D3 : a 192-Kbps communication channel between STEs.

o Used for alarms, maintenance, control, monitoring, administration,and other communicaiton needs.

o In an STS-N signal, this channel is defined for the 1 st STS-1 only.The other N-1 E1¶s are not used.

STS 1 section overhead



STS-1 section overhead

Line Overhead : SONET




Located in the row 4-9 of the overhead section, totally 45bytes.H1, H2 :offset between the pointer and the first S P E byte.H3 : an action byte for frequency justification.o It carries valid payload if the justification is negative.BIP -8 : Used for locating errors.o It is calculated using even parity over the STS-1 for the

previous frame after scrambling and placed in B2before scrambling the current frame.

K1, K2 : for automatic protection switching.o In STS-N, this is defined for #1 only.

STS 1 line overhead



STS-1 line overhead





D4 to D12 : a 576-Kbps communication channel between LTE for o Alarmso Maintenanceo Controlo Monitoringo

Administrationo Other communication needso In STS-N, this is defined for #1 onlyZ1, Z2 : not defined except in STS-N for #3, in which Z2 is onlydefined as line far-end block error ( F EBE ).E2 : an express 64-Kbps communications channel between LTEo In STS-N, this is defined for #1 only

P ayload P ointers : H1 H2 H3



P ayload P ointers : H1, H2, H3

NDF ( New Data F ound flag ) : first 4 MSB in the H1 byteo ³ normal = 0110 ³ for the following 3 possible situations :

No frequency justificationP ositive frequency justification has taken placeNegative frequency justification has taken place

o ³ set = 1001 ³: an arbitrary ( and significant ) change of the pointer

vaule has occurred due to a change of data position in the S P ES-bits : the size of the virtual tributary in the payloadI-bit / D-bit word : for incrementing / decrementing the offset

o P erform frequency justification in conjunction with the H3 byteH3 : a payload byte opportunity buffer when positive or negative

justifications are necessary

P ayload pointers : H1 and H2



P ayload pointers : H1 and H2

P ointer H3 ± frequency justification



P ointer H3 ± frequency justification

F unctions of H1 H2 and H3



F unctions of H1, H2 and H3

Identifies that a change has occurred in the pointer value ( ND F = 1001 ) due to an intermittent synchronization in the node wherethe new start is ( I + D bits ).Identifies that a change may have occurred in the pointer value (0110 ) due to a frequency difference between node and incoming

frequency.o Received frequency may be slightly higher or lower than the

node frequency.o Either more or fewer bits are received that what the S P E can

fit.o If the received frequency is higher ( lower ), then node will

perform a negative ( positive ) frequency justification.The I-bit / D-bit words value will indicate whether negative or positive frequency justification is needed.

payload 4(part1)

Documents