TopicsSampling PCM PrinciplesPDH & SDH SystemsSTM 1 Frame structureBit rates of STM-1 ,STM-4 ,STM-16

Sampling TheoremA bandlimited signal can be reconstructed exactly if it is sampled at a rate atleast twice the maximum frequency component in it. Fs 2Fm

PULSE CODE MODULATION

Developed by A.M.Reaves in 1938Uses TDM techniqueVoice Frequency ranges upto 4 KhzSampling the Voice Signal @ 8 Khz (Ts=125 sec)8 bits per sampleDigital Bit Rate: 8000 X 8 = 64 Kbps

BUILDING UP THE BASE STREAM (2MB)

One sample duration (approx) = 4 sDuration between samples = 125 s

30 Channel PCM System30 voice channelsOne channel for synchronisation One channel for signallingTotol no.of channels =32One frame (125 s) is divided into 32 time slots

PCM bit rate32 time slots in a frameEach slot having 8 bitsTotal no.of bits per frame= 32*8 =256 bits/frameTotal no.of frames per sec =8000Total no.of bits per sec =256 * 8000 =2048 Kbps

PDH

Plesiochronous Digital Hierarchya technology used in telecommunications network to transport large quantity of data over digital transport equipment such as fibre optic and microwave radio wave systems.the term plesiochronous is derived from greek plesio which means near, and chronous, time.it means that pdh networks run in a state where different parts of the network are almost, but not quite perfectly synchronisedThe basic data rate is 2.048 Mbps

PDH BIT RATES(European standard)E1- 2048 Kbps (2Mb) [30 Voice Channel]E2- 8448 Kbps (8Mb) [120 Voice Channel]E3- 34368 Kbps (34Mb) [480 Voice Channel]E4- 139264 Kbps (140Mb) [1920 Voice Channel]

2 Mbps8 Mbps34 Mbps140 Mbps140 Mbps34 Mbps8 Mbps2 Mbps

PDH HIERARCHY

Limitations of PDHSpecialized equipment required for interwork two hierarchyInability to identify individual channels in a higher order bit stream.Insufficient capacity for network managementHigher bit rates are difficult to achieveSupports only linear topologyno common standards among vendors.

SDH-Synchronous Digital HierarchySDH is an ITU-T standard for a high capacity telecom network. SDH is a synchronous digital transport system, aim to provide a simple, economical and flexible telecom infrastructure. This is the information structure used to support information payload and overhead information organized in a block frame structure which repeats every 125 micro secondsThe basis of Synchronous Digital Hierarchy (SDH) is synchronous multiplexing - data from multiple tributary sources is byte interleaved.

MERITS OF SDHSimplified multiplexing / demultiplexing techniquesDirect access to lower speed tributariesEnhance Operation , Administration & MaintenanceEasy growth to higher bit rates in steps with evolution of transmission technologyCapable of transporting existing PDHCapable of transporting future ATM Capable of operating multi vendor and multi operator environment

SDH RatesSDH is a transport hierarchy based on multiples of 155.52 Mbit/s. The basic unit of SDH is STM-1STM-Synchronous Transport ModuleHigher rate is an exact multiple of the lower rate therefore the hierarchy is synchronous. STM-NWhere N =1,4,16 ,64 n is a multiples of four

SDH BIT RATES

SDH LevelsBit rates in MbpsSTM-1155.520 STM-4622.080STM-162488.320STM-649953.28

STM-1 Frame Synchronous Transport Module A frame with a bit rate of 155.52 Mbit/s is defined in ITU-T Recommendation G.707It is made up from a byte matrix of 9 rows and 270 columns.

SDH FRAME REPRESENTATION9

* As indicated in the figure, the STM n signal is multiples of frames consisting of 9 rows with 270 bytes in each row

The order of transmission of information is first from left to right and then from top to bottom

The first 9 bytes in each row are for information and used by the SDH system itself.This area is divided into 3 parts

Regenerator Section Overhead(RSOH) Multiplex Section Overhead(MSOH) Pointers

STM-1 frame structure (contd..)

THE TRUCK ANALOGYPAYLOAD OVERHEAD

THE TRUCK ANALOGYPAYLOAD OVERHEAD

THE TRUCKPAYLOAD OVERHEAD

RSOH: Regenerator section overheadMSOH: Multiplex section overheadPayload: Area for information transport

Transport capacity of one Byte: 64 kbit/sFrame capacity: 270 x 9 x 8 x 8000 = 155.520 Mbit/sFrame repetition time: 125 s13594270270 Columns (Bytes)19transmitrow by rowRSOHMSOHAU PointerPayload(transport capacity)SDH Frame Structure

(MATRIX REPRESENTATION)1ST ROW2ND ROW3RD ROW9 261 9 261 9 261 9 261 III9261PAY LOADSOHII2709TH ROWFRAME REPRESENTATION

BIT RATE : STM-NNUMBER OF ROWS = 9NUMBER OF COLUMNS = 9+261=270NUMBER OF BYTES = 9x270NUMBER OF BITS = 9x270x8NUMBER OF BITS / SECOND = 9x270x8x8000=155520000=155.520 Mbps (STM-1)BIT RATE OF STM-N = (Nx155.520) Mbps

SDH ACCOMMODATES EXISTING SIGNALS

C4C3C1263

1SDH

MUX31

SDH MultiplexingThe multiplexing principles of SDH follows these termsMapping - A process used when tributaries are adapted into Virtual Containers (VCs) by adding justification bits and Path Overhead (POH) information.Aligning - This process takes place when a pointer is included in a Tributary Unit (TU) or an Administrative Unit (AU), to allow the first byte of the Virtual Container to be located.Multiplexing - This process is used when multiple lower-order path layer signals are adapted into a higher-order path signal, or when the higher-order path signals are adapted into a Multiplex Section.

Multiplexing Structure

*Elements of SDH Container (C) Virtual Container (VC)

Tributary Unit (TU)

Tributary Unit Group (TUG)

Administrative Unit (AU)

Administrative Unit Group (AUG)

Synchronous Transport Module - N (STM N)

CONTAINERInput is PDHProvides justification for PDH signalsOutput is synchronousCONTAINERSDHPDHJUSTIFICATION2Mb/ssynchronized34 BYTES

VIRTUAL CONTAINER35 BYTES - ONE 2MBCONTAINERPOH

TRIBUTARY UNITWhen pointer is added to the virtual container ,it is called tributary unit ( ONE 2 MB)VCPOINTER4 X 936 BYTES

TRIBUTARY UNIT GROUP-2

4 X9 4 X9 4 X9TU12(1)TU12(2)TU12(3)TUG-2

12 X9TU12 CONTAINS -ONE 2 MBTUG-2 CONTAINS THREE 2MB

Tributary unit group -3Homogeneous assembly of identical tributary units

Tug-2(1)Tug-2(7)TUG-3TUG-3 CONTAIS 21X2MB

VC-4 FORMATIONVirtual container formation

TUG-3

TUG-3

TUG-3

VC-4=261

VIRTUAL CONTAINER -4Virtual container 258C + 1C POH+ 2C fixed stuff byte

258+1+2=261Columnsvc

AU POINTER IS ADDED TO THE VC

ADMINISTRATIVE UNIT GROUPSOH BYTES ARE ADDED

270C X 9RPAY LOADRSOHMSOH

The following are the different steps in the mapping of 2Mbps streamFormation of container C12Formation of virtual container VC12Formation of tributary unit TU12Multiplexing of TU12 s to form TUG3Multiplexing of TUG3s to form VC4Formation of administrative unit AU4Formation of administrative unit group AUGAdding SOH to form STM1

MUX PRINCIPLE: STM-1(from C-12)

E1: 2.048Mb/sx3x7x3Synchronous Transport ModuleAdministrative Unit Group: One or more AU(s)Administrative Unit: VC + pointersVirtual Container: payload + path overhead

E3: 34.368Mb/sDS3: 44.736Mb/sx3Synchronous Transport ModuleAdministrative Unit Group: One or more AU(s)Administrative Unit: VC + pointersVirtual Container: payload + path overheadMapping of 34 Mbps stream

Synchronous Transport ModuleAdministrative Unit Group: One or more AU(s)Administrative Unit: VC + pointersVirtual Container: payload + path overheadMapping of 140 Mbps streamE4: 139.264Mb/s

SDH End-to-End ConnectionPTEMSTEMSTEPTESTM-1STM-NSTM-NREGSTM-NSTM-1REGMultiplex sectionPathPDHPDHRegenerators sectionSDH

Section OverheadRSOH Regenerator Section OverheadMSOH Multiplex Section Overhead

SECTION OVERHEADSMSOHRSOH

A1A1A1A2A2A2J0XXB1E1F1XXD1D2D3AU POINTERB2B2B2K1K2D4D5D6D7D8D9D10D11D12S1M1E2XX

SOH BYTE ALLOCATION

A1,A2 Frame alignmentB1B2Error monitoringD1..D3Data communication channel for RSOHD4..D12Data communication channel for MSOHE1-E2Order wire channelF1MaintenanceJ0STM IdentifierK1 K2Automatic protection switchingS1SYNCHRONISATION STATUSM1Txmn Error acknowledgementMedia dependent bytes

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