Pdh

Multiplexing.

Used when the total medium transmission capacity exceeds the channel’s one. Channels are multiplexed for a better use of medium. Useful for long-haul communications; trunks are fiber, coaxial, microwave high capacity links. Higher data rate transmission Better cost-effective transmissions for a given application over a given distance.

Multiplexing

Under the simplest conditions, a medium can carry only one signal at any moment in time.

For multiple signals to share one medium, the medium must somehow be divided, giving each signal a portion of the total bandwidth.

The current techniques that can accomplish this include time division multiplexing, frequency division multiplexing, and wavelength division multiplexing.

Multiplexing (Conti…)

Techniques

TDM : Time Division MultiplexingTime Division Multiplexing

synchronous

statistical

FDM : Frequency Division MultiplexingFrequency Division Multiplexing

WDM : Wavelength Division MultiplexingWavelength Division Multiplexing – for optical transmissions

CDM : Code Division Multiplexing

Time Division Multiplexing Sharing of the signal is accomplished by dividing available transmission time on a medium among users.

Digital signaling is used exclusively.

Time division multiplexing comes in two basic forms:

1. Synchronous time division multiplexing, and

2. Statistical, or asynchronous time division multiplexing.

Synchronous Time Division Multiplexing

The original time division multiplexing.

The multiplexer accepts input from attached devices in a round-robin fashion and transmit the data in a never ending pattern.

T-1 and ISDN telephone lines are common examples of synchronous time division multiplexing.

Synchronous Time Division Multiplexing (Conti….)

If one device generates data at a faster rate than other devices, then the multiplexer must either sample the incoming data stream from that device more often than it samples the other devices, or buffer the faster incoming stream.

If a device has nothing to transmit, the multiplexer must still insert a piece of data from that device into the multiplexed stream.

Statistical Time Division Multiplexing

A statistical multiplexer transmits only the data from active workstations.

If a workstation is not active, no space is wasted on the multiplexed stream.

A statistical multiplexer accepts the incoming data streams and creates a frame containing only the data to be transmitted.

Frequency Division Multiplexing (FDM)

A number of signals carried simultaneously, each signal modulated onto a different carrier frequency, which are separated for avoiding signals bandwidths to overlap (use of guard bands).

Input signals are analog or digital, converted to analog, multiplexed onto an analog composite signal.

Frequency Division Multiplexing (conti..)

Assignment of non-overlapping frequency ranges to each “user” or signal on a medium. Thus, all signals are transmitted at the same time, each using different frequencies.

A multiplexer accepts inputs and assigns frequencies to each device.

The multiplexer is attached to a high-speed communications line.

A corresponding multiplexer, or demultiplexer, is on the end of the high-speed line and separates the multiplexed signals.

Wavelength Division Multiplexing Wavelength division multiplexing multiplexes multiple data streams onto a single fiber optic line.

Different lasers transmit multiple signals at different wavelengths.

Each signal carried on the fiber can be transmitted at a different rate from the other signals.

Dense wavelength division multiplexing combines many wavelengths (30, 40, 50, 60, more?) onto one fiber.

Coarse wavelength division multiplexing combines only a few wavelengths.

Code Division MultiplexingCode Division Multiplexing

CDM allows signals from a series of independent sources to be transmitted at the same time over the same frequency band.

This is accomplished by using orthogonal codes to spread each signal over a large, common frequency band.

The technique used is Spread Spectrum

PLESIOCHRONOUS DIGITAL HIERARCHY

IntroductionIntroduction

• Plesiochronous is a Greek word meaning Plesiochronous is a Greek word meaning Almost Almost SynchronousSynchronous , but not fully synchronous. , but not fully synchronous.

• In Plesiochronous system every equipment is generating In Plesiochronous system every equipment is generating its own clock for synchronization.its own clock for synchronization.

Generation Of PCM Signal(Digital Signal)

DS0 Signal Derivation DS0 Signal Derivation

PCM Line SamplingPCM Line Sampling

Each sample is 8 bits wide: the resulting signal rate will be8 bits x 8,000 samples/second = 64,000 bits/second, hence

• Sampling rate = 8,000 samples/second – how?

• Nyquist Theorem: sampling rate = 2 x highest audible frequency (4,000 Hz)

2 x 4,000 = 8,000 samples/second

1 DS0 = 64 Kb/s1 DS0 = 64 Kb/s1 DS0 = 64 Kb/s1 DS0 = 64 Kb/s

Analog Signal

tt

fftt

PDH Bit RatesPDH Bit Rates

North AmericaEurope Japan

DS1 FrameDS1 Frame

FF CH 1CH 1 CH 2CH 2 CH 19CH 19 CH 20CH 20 CH 21CH 21 CH 22CH 22 CH 23CH 23 CH 24CH 24

192 Bits of Encoded Voice (24 Channels)192 Bits of Encoded Voice (24 Channels)FramingFramingBitBit

Total bits per DS1 frame = 192 + 1 = 193 bitsTotal bits per DS1 frame = 192 + 1 = 193 bitsSampling rate = 8,000 samples/secondSampling rate = 8,000 samples/second

DS1 RateDS1 Rate = 193 bits x 8,000 samples/second = 193 bits x 8,000 samples/second = = 1.544 Mb/s1.544 Mb/s

DS1Signal DerivationDS1Signal Derivation

DS3 SignalDS3 Signal

Higher Rate signal

1 DS3 = 28 DS1s / 672 DS0s

Line Rate

1 DS3 = 28 * (Line rate of DS1s) + overhead and framing bits

= 44.736 Mbps

LevelLevel

VF(DS0)DS1DS1CDS2DS3Proprietary

64 Kb/s1.544 Mb/s3.152 Mb/s6.312 Mb/s

44.736 Mb/s~ 565 Mb/s

Line RateLine Rate CapacityCapacity

1 voice circuit24 voice circuits2 x DS1 = 48 VF4 x DS1 = 96 VF

28 x DS1 = 672 VF12 x DS3 = 8,064 VF

Physical MediaPhysical Media

Copper wireCopper wireCopper (screened)Copper, µwave, fiberµwave, fiberSingle-mode fiber

North American HierarchyNorth American Hierarchy

Hierarchy breaks down above the DS3 level

Asynchronous bit-stuffing penalties mount

OC-11

OC-n1

x n

Is equivalent to

Electrical (sync) Optical (sync)

STS-11

x n

STS-n1

DS11 VT1.5/C111

DS31 STS-1/C31

x 28 x 28

Maps into

Maps into

Asynchronous Synchronous (SONET/SDH)

Is equivalent to

Signal EquivalenceSignal Equivalence

Async. - HierarchyAsync. - Hierarchy

Bit StuffingBit Stuffing

Pleisochronous MultiplexingPleisochronous Multiplexing

HIGHER ORDER MUX

MUX

Bit-Interleaved Multiplexing Bit-Interleaved Multiplexing

•It is TDM

•One bit will be taken from all Tributaries.

TYPICAL OPTICAL LINK• PDH

o TERMINAL EQUIPMENT

MUX

OLTE

o REGENERATOR

PDH NETWORK ELEMENTS

U-Links

AlarmsAlarms

Switch

PWR & ALM Unit

Channel Unit

Interface Unit

MUX

MUX BLOCK (INSTALLED IN THE MUX RACK)

2 Mbps

M13 MUX2 Mbps

2 Mbps

2 Mbps

34 Mbps

JUMP MUX

Laser Shut Off

Laser ON

Error Major

Error Minor

LSOD LOF

LOS

AIS

Power On(Green always)

Error major

Error Minor

Optical Adapter

Switch

Alarm Monitor

Power & Alarm Unit

Tx Unit Rx Unit

OLTE(Optical Line Terminating Equipment)

(INSTALLED IN THE OLTE RACK)OLTE BLOCK

COMPRISES OF MUX & OPTICAL UNITS

OPTIMUX

(ACCOMODATES BOTH - OLTE & MUX) MIX RACK

REG RACK

Limitations Of PDHLimitations Of PDH

PDH Frame start

start

start

start

start

Identifying exact location of frame is difficult.

LimitationsLimitations

Multiplexing / Demultiplexing is time consuming

Limitations (contd..)Limitations (contd..)

140 Mbit/s

34 Mbit/s

565Mbit/s

8 Mbit/s

2 Mbit/s

140-

565

MU

X &

LTE

140-

565

MU

X &

LTE

34-1

40 M

UX

34-1

40 M

UX

8-34

MU

X

8-34

MU

X

2-8

MU

X

2-8

MU

X

Drop & Add

Pdh.exe

SDH Transport SystemsSDH Transport Systems

Synchronous Digital Hierarchy-The work Synchronous Digital Hierarchy-The work House of Telecommunication House of Telecommunication

SYNCHRONIZATION OF DIGITAL SIGNAL :SYNCHRONIZATION OF DIGITAL SIGNAL :

In a set of Synchronous signals, the digital transitions in the signals occur at exactly the same rate. There may be a phase difference between the transitions of the two signals, and this would lie on specified limits.

In a synchronous network, all the clocks are traceable to one primary reference clock (PRC). The accuracy of the PRC is better than 0.1 in 1011 and is derived from a cesium atomic standard.

SYNCHRONOUS SIGNAL:

SYNCHRONIZATION OF DIGITAL SIGNAL :SYNCHRONIZATION OF DIGITAL SIGNAL :

ASYNCHRONOUS SIGNAL:If two digital signals are Asynchronous then their transitions

occur at “entirely” different rate.

The two digital signals are out of phase

Which implies that all the digital signals are not synchronized to a common clock

If two digital signals are plesiochoronous then their transitions occur at “almost” the same rate, with any variation being constrained within tight limits. Although this clocks are extremely accurate, there is a difference between one clock and the other.

PLESIOCHRONOUS SIGNAL:

Requirement Of Synchronous Digital Hierarchy ( SDH )Requirement Of Synchronous Digital Hierarchy ( SDH )

Need for extensive network management capability within the hierarchy.

Standard interfaces between equipment.

Need for inter-working between north American and European systems.

Facilities to add or drop tributaries directly from a high speed signal.

Standardization of equipment management process.

Typical Example of SDH SystemTypical Example of SDH System

622.08Mbit/sSTM-4

155.52Mbit/sSTM-1

Bit RateSDH

STM-16STM-16 2488.32Mbit/s

STM-64 9957.28Mbit/s

Product

TN-1X

TN-4XE

TN-16X

TN-64X

The Network Elements of SDH Network :

Regenerator (Reg.)

Terminal Multiplexer (TM)

Add/Drop Multiplexer (ADM)

Digital Cross Connect (DXC)

STM-NSTM-N STM-NSTM-NRegeneratorRegenerator

Regenerator (Reg.)

It regenerates the clock and amplifies the incoming distorted and attenuated signal.

It derive the clock signal from the incoming data stream.

RegeneratorRegenerator

Terminal Terminal MultiplexerMultiplexer

STM-NSTM-NPDHPDHSDHSDH

Terminal Multiplexer (TM)

It combines the Plesionchronous and synchronous input signals into higher bit rate STM-N Signal.

Terminal MultiplexerTerminal Multiplexer

Add/Drop Multiplexer (ADM)

STM-NSTM-NSTM-NSTM-N

PDHPDH SDHSDH

Add / Drop Add / Drop MultiplexerMultiplexer

Add/Drop MultiplexerAdd/Drop Multiplexer

Extraction from & insertion into high speed SDH bit streams of Plesiochronous and lower bit rate synchronous signal.

ADM makes possibilities of

Ring structure of network which provides the advantage of automatic back-up path switching in the event of fault.

STM-16STM-4STM-1

140 Mbit/s34 Mbit/s2 Mbit/s

STM-16STM-4STM-1

140 Mbit/s34 Mbit/s2 Mbit/s

Cross - Connect

Digital Cross Connect (DXC)

Digital Cross Connect (DXC)

Digital Cross Connect:

A digital cross connect is an equipment which has the capability of interconnecting tributaries

An Agg to Agg connection, a trib to aggregate connection and a tributary to tributary connection is also possible in case of a Digital Cross Connect

PDHATMIP

SDHSDHmultiplexermultiplexer

SDHSDH RegeneratorRegenerator

##Cross-Cross-

connectconnect

SDHSDHmultiplexermultiplexerSDH SDH SDH

PDHATMIP

Regenerator Section

Regenerator Section

Multiplex Section Multiplex Section

Path

TYPICAL LAYOUT OF SDH LAYER

General view of Path Section designations