Communication Systems

CONTENTS „

Introduction

„

Generic Telecom Networks

„

Basic Concepts & Transmission Media

„

A t Antennas &P Propagation ti

„

Signalling, Switching & Transmission

„

Optical Networking

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CONTENTS

ƒ ƒ ƒ ƒ ƒ ƒ

D t Communication Data C i ti Broadband Access Systems Wireless Networks (Microwave, Satcom & Radar) Mobile / Cellular Communication (1G to 22.5G) 5G) Bluetooth & WLAN Future Trends (3G / 4G, VOIP, NGN)

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Introduction What is Telecommunication ?

ƒ Technology that enables Multi Multi-media media Communication between subscribers located anywhere, at any time.

ƒ Deals with Communication of Voice / Data / Video Message signals from Source to Destination at acceptable quality levels, using various Wireline / Wi l Transmission Wireless T i i Media. M di

ƒ Viewed as Infrastructure like Power, Roads, Ports, T Transport t etc t . March 2006

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I t d ti Introduction Major Milestones in Telecom Evolution ƒ ƒ ƒ ƒ ƒ ƒ ƒ ƒ ƒ ƒ

Invention of Telegraph & Telephone Instruments Birth of Telephone Exchanges & Wireline Communication Advent of Wireless Communication Establishment of Long Distance Communication Networks (Submarine Cables / Fiber Optics / Microwave / Satcom) Use of Computers in Electronic Exchanges Advances in DSP / Data Communication & Convergence Evolution of Internet & World Wide Web India adopts National Telecom Policy, opening up Telecom Sector Mobile Communication Services (GSM & CDMA) expand with focus on Introduction of Broadband Services, improving Teledensity / QOS and Cost reduction. New Technologies such as ATM / GbE, IP / MPLS, Optical Networking, 3G / 4G Mobile, Wi-Fi / Wi-MAX, VOIP, IPTV etc emerging. March 2006

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Introduction Telecom Boom India reaches 125 Million mark in Phone connections (Land Lines & Mobiles); Large Subscriber base after China, US, Japan & Germany Mobile Growth > Growth of Land Lines Present Teledensity in India > 11 % (Fixed 4 % & Mobile 7 %), as against a total of 1.6 % in 1997 & 2.9 % in 2000 Expected to reach 25 % Teledensity in next 2 to 3 Years. Decrease in Call charges Liberalization of NLD / ILD Services & VOIP Services. March 2006

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Introduction Telecom Value Chain ƒ Chip Manufacturers ¾ TI, Analog Devices, Philips, National Semiconductors, Intel etc. ƒ Terminal Devices Manufacturers ¾ Nokia, Motorola, LG, Samsung etc ƒ Network N t kE Equipment i tM Manufacturers f t / Vendors V d ¾ Ericsson, Nortel, Nokia, Motorola, Lucent, Cisco etc ƒ Service Providers ¾ Telecom Software Companies, Project Contractors etc. ƒ Network Operators (Basic, Mobile & MSOs) ƒ Subscribers March 2006

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Introduction Major Telcos (Integrated Service Operators): ƒ BSNL, Bharti, Tata & Reliance. Telecom Standardization Organizations / Regulators FCC: Federal Communication Commission ISO International ISO: I t ti l Organization O i ti for f Standardization St d di ti ITU: International Telecommunications Union ANSI:American National Standards Institute EIA / TIA: Electronics / Telecom Industries Association ETSI: European Telecommunication Standards Institute WPC, TRAI (DOT): In India March 2006

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Generic Telecom Networks

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Generic Telecom Networks Public Switched Telephone Network (PSTN) Cellular Mobile Communication Network Data / IP Network CATV Network Hybrid / Integrated Network March 2006

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Generic Telecom Networks PSTN Architecture ((Exchange g Hierarchy) y) State-level Trunk Exchange Area-level Trunk Exchange Local Exchange Subscribers

ƒ PSTN: A wide area, circuit switched, partially connected mesh network of star connected sub networks. State TE

State TE Area TE

Town area LE Metro area LE March 2006

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Generic Telecom Networks PSTN Connectivity y ISP Internet

RAS Local Loop Subscribers 1 2

M D 1 EXCHANGE DP/ D D 2 CCP (Multi F (SWITCH) F m

Trunks

MUX / Baseband DEMUX

TX / RX

Pair)

n

CPE TP Copper Lines

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To Destination Exchange / Subscribers

DE-MUX / MUX SC

RX / TX

Media

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Generic Telecom Networks Access N A Network t k (Di (Distribution) t ib ti ) „ Local Loop / Point to Multipoint „ W Wireline e e / Wireless W e ess Backbone Network (Transmission) „ Long Distance / Point to Point „ Wireline / Wireless Public Switched Telephone Network (PSTN) „ Signalling, Switching & Transmission Systems „ Dedicated Circuit Switching Overlay Networks „ Cellular C ll l (Mobile), (M bil ) Internet I / Data D (Packet (P k Switching) S i hi ) etc. March 2006

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Generic Telecom Networks Typical Mobile Communication Network Base Station 1

Base Station Controller

Mobile Station

MSC Base Station 2 BSC

MS Mobile Station March 2006

OMC

BSC

MS

(Handset)

Data Bases

Base Transreceiver Station (BTS)

Mobile M bil Switching Center

G M S C

PSTN

SMSC / VMSC

Base St B Station ti Controller SC

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Generic Telecom Networks CATV Network with HFC (Hybrid y Fiber Coaxial) Access

Satellite Feed

Head End Fiber PSTN / IP

Optical Distribution Node

Coax

Tapp

Amplifier

Local Programs

Fiber & Coaxial cable for Distribution of Multimedia Services. March 2006

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Basic Concepts

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Basic Concepts ƒ

Voice Signal – Analog (continuous) – Low bandwidth (15 KHz Band limited to 4KHz for conventional telephony) p y) – Transmission can be Analog or Digital.

Data Signal – – – –

Digital (discrete), Bursty Low & High Speed; PC / LAN / FAX Variable bandwidth (Few bps to 10 Gbps & beyond) Transmission a s ss o ca can be Analog a og or o Digital g ta

Video Signal – Analog (continuous) – High bandwidth (5 MHz Typical) – Transmission can be Analog or Digital March 2006

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Basic Concepts Analog

Si Signal l

ƒ

Voice is an Analog (continuous) signal and Data is a Digital (discreet) signal.

ƒ

Analog to Digital Converter (ADC): ƒ Used to digitize voice signal in transmit side. Digital to Analog Converter (DAC): ƒ Used for re-conversion at the receive side. eg. PCM Codec C d

ƒ ƒ ƒ

DAC used also for Data Transmission over existing Analog communication medium (eg PC Modem, (eg. Modem FAX, FAX VFT etc). etc) March 2006

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1 0 1 1 0 1 1 1

Digital 17

B i Concepts Basic C t Voice Traffic

ƒ ƒ

Analog Voice signal band limited to 4 KHz for Plain Old Telephone System (POTS); Higher Bandwidth for Broadcast. Voice Traffic in Telephony measured in Erlang units (One Call Hour).

ƒ

ƒ

Erlang – B & C formulae represent Grade of Blocking Probability & Queuing Delay.

Service in terms of

Received Voice Quality is measured by Signal to Noise Ratio (SNR) in dB. dB 30 db SNR implies that signal is 103 times noise on the average (Telephone Voice quality and AM broadcast quality). „ 45 db SNR implies i li th thatt the th signal i l is i about b t 3 x 104 times ti noise i on an average (Very good as available in Hi-Fi FM broadcast). „

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Basic Concepts Relative Power unit db : 10 Log10 P2 / P1 10 log l 10 ( P2 / P1 ) = 0 db, db when h P2 = P1 10 log10 ( P2 / P1 ) 10 log10 ( P2 / P1 ) 10 log10 ( P2 / P1 ) 10 log10 ( P2 / P1 ) 10 log10 ( P2 / P1 ) 10 log10 ( P2 / P1 ) March 2006

= = = = = =

3 db, when P2 = 2 P1 6 db db, when hen P2 = ? -3 db, when P2 = ? 10 db, db when P2 = 10 P1 20 db, when P2 = 100 P1 23 db, when P2 = ? SC

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Basic Concepts Absolute Power unit dbm Power in dbm 1 mW 2 mW 4 mW 10 mW 100 mW 0 5 mW 0.5 W 0.1 mW 1 µW 1W March 2006

= 10 log10 (Power in mW) = = = = = = = = =

10 log10(1) dbm = 0 dbm 10 log10(2) dbm = + 3 dbm ? + 10 dbm; 40 mW = ? + 20 dbm; 250 mW = ? -33 dbm; db 5 mW W=? -10 dbm -30 dbm + 30 dbm; 1 KW = ? SC

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Basic Concepts

D t T Data Traffic ffi

ƒ Data Traffic is measured by Bit Rate ( Data Rate/Throughput) in Bps / Kbps / Mbps / Gbps etc.

ƒ

Q Quality y of Data Reception p is measured byy Bit Error Rate (BER), the rate at which errors take place; 10-6 BER implies one bit error received for a million bits transmitted on an average. Video Transmission

ƒ Analog or Digital; It could be Compressed or of Studio Quality. Quality March 2006

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Basic Concepts Transmission Media

Wire line

Copper Cable

Twisted Pair (TP) March 2006

Coaxial

Wireless

Fixed

Fiber Optic Cable

Single M d Mode Fiber

Mobile

Multi M d Mode Fiber SC

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Basic Concepts Electromagnetic Spectrum (Frequency Bands) RF f

300 Hz

30 kHz

VLF

( AF )

λ

3 MHz

300 MHz

30 GHz

3 THz

300 THz

LF/MF HF/VHF UHF/SHF EHF

Infrared Visible UV

1m

1μm μ

10 Km

100m

Light

1 cm

Twisted Pair Coaxial Cable Radio

TV

Microwave

Optical p Fiber

Wavelength = = Velocity of Light (c) / Frequency (f ) RF ((UHF)) - Wireless Medium for Mobile communication. Infrared (IR) – For Fiber Optic Core Transmission Networks. „

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Basic Concepts Copper Media

ƒ

Types of Transmission Lines:

ƒ ƒ ƒ ƒ

ƒ ƒ ƒ

Can be represented by Equivalent Circuit with L, R, C & G per unit length. Balanced: Twin Lead / Twisted Pair (UTP/ STP) for lower Frequency applications. Unbalanced: Coaxial (Thin / Thick) Cables for Higher frequencies such as VHF / UHF; Support TEM wave propagation. Wave Guides: Used above Cut off frequencies of several GHz; Support TE or TM modes.

Characteristic Impedance:

ƒ

Input Impedance of line of infinite length or of a line of finite length, terminated by Characteristic Impedance. Standing Wave Ratio (SWR): Caused by reflections from imperfect termination; Forward & reflected waves set up an interference pattern. S ith Ch Smith Chart: t Polar P l Impedance I d diagram di enables bl calculation l l i off Z or Y or SWR at any point on line with any load. March 2006

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Basic Concepts ƒ

Typical Characteristic Impedance Values: ƒ ƒ

600 & 120 Ohms Balanced (TP) 50 & 75 Ohms Unbalanced (Coaxial).

ƒ

V lt Voltage R fl ti Coefficient Reflection C ffi i t (ρ ( v): ) Reflection due to Impedance

ƒ

mismatch with Load, resulting in Standing Waves. VSWR (s): Voltage Standing Wave Ratio. ƒ s = 1+ρ / 1−ρ ; ρ = s –1 / s + 1 ; Return Loss (dB) = 20 log (1 / ρ).

ƒ

Transmission Line examples: ¾ ¾ ¾ ¾ ¾

Twin Lead (Balanced) : TV Antenna Lead T i d pair Twisted i (Balanced) (B l d) : Local L l Loop L for f Telephony T l h UTP, STP : LAN Cabling Coaxial ( Unbalanced ) : Antenna Feeders, RF Cabling, CATV Access Wave guides: Microwave Antenna feeds

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Basic Concepts Copper Media Outer Conductor

Coaxial Cable „

„

„

„

3 Concentric Elements (Inner Conductor, Dielectric & Outer Conductor) form the Transmission Line. The Materials & Dimensions of these elements determine the eelectrical ect ca ccharacteristics. a acte st cs. Protective Plastic Sheath around the Outer Conductor. Capable of supporting Transmission of RF Signals (upto 3 GHz).

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Di l Dielectric i Inner Conductor

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Basic Concepts Copper Media Wave guides: „ „ „

„ „ „ „ „

A pipe type Transmission Line with Rectangular or Circular Cross section. ti No Inner conductor nor supporting Dielectric. Supports TE (No component of Electric field in the direction of Propagation) p g ) or TM (No ( component p of Magnetic g field in the direction of Propagation) modes. Probe / Loop / Slot coupling for excitation. Adaptor to couple to Coax cables. Accessories: Flanges, Joints, bends etc. Cavity Resonators: WG closed at both ends act as Tuned Circuits. Aux. Components: Directional Couplers for measurements, Isolators & Circulators made of ferrites. ferrites

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Basic Concepts Optical p Fiber

ƒ

Purpose: − Propagation of Light waves carrying Electrical signals.

Geometry

Core Cladding Silicone Coating

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Buffer Jacket

Strength Members Outer Jacket 28

Basic Concepts Fiber Media (Fiber Optic Cable) Function: Transmission of Electrical signals thro’ light waves in a gglass medium. Application: For Broadband & Long distance communication. ƒ Examples: Telephone Trunk circuits / Backbone Networks, WAN, CATV Networks, Networks FTTH etc. ƒ Submarine Cables provide International Broadband Communication.

ƒ

Technology: Uses Total Internal Reflection inside an Optical Fiber, ib consisting i i essentially i ll off inner i Core & Cladding l ddi outside; id Refractive Index, µ, decreases from Core to Cladding, gradually or abruptly. March 2006

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Basic Concepts p Fiber Media (Fiber Optic Cable)

ƒ Fiber Types: ƒ Single i Mode (Smaller ( ll Core dia) di ) for f long l haul h l

ƒ ƒ

applications. ƒ Multimode ((Larger g Core dia)) for shorter distance coverage; Step Index & Graded Index versions available. Fibers with 1310 nm & 1550 nm wavelengths as optical windows. Multi Fiber Cable: Indoor & Outdoor (Buried / Aerial).

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Basic Concepts Fib Media Fiber M di (Fiber (Fib Optic O ti Cable) C bl )

ƒ

Characteristics:

ƒ Attenuation: Reduction of signal strength in db / km; 1550 nm fiber has lower attenuation ( 0.2 db / km typical).

ƒ Dispersion: Leads to Pulse spreading / Optical Signal broadening wrt distance; 1310 nm SMF has least dispersion.

ƒ

Splicing & Connectorization: Means of joining two fibers.

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B i Concepts Basic C t Basic Fiber Optic p System y Transmitter Electrical

Si l Signal IN

Receiver Fiber Optic p Cable

Electrical

Signal

SI Fiber

OUT

GI Fiber SM Fiber Fib Transmitter ((LED or LASER)) converts an electrical signal g into a light g signal. g Receiver (Photodiode) converts the light signal back into an electrical signal. March 2006

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B i Concepts Basic C t

ƒ

Low loss

Fiber Optic Fib O ti Disadvantages Di d t ƒ Minimum bending radius required q

ƒ

No EMI

ƒ

ƒ

Small physical size and weight

Nonconductor; Cannot transmit power feed along with transmission as in telephony

ƒ

Tap proof

ƒ

High cost in low bandwidth and short distance applications

Fiber Optic Fib O ti Advantages Ad t ƒ High bandwidth

ƒ

Safe - Doesn’t carry electrical current, current no shock hazard March 2006

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RF / Wireless Basics Wireless Media

ƒ

Electromagnetic Waves travelling in free space with Velocity of light, are used as wireless media.

ƒ

Message signals superimposed on Carrier signals (Transverse EM Waves) are radiated by Antennas for Transmission and Reception. Frequency Bands are allocated for various applications ( Fixed & Mobile). ¾ Frequency Bands: Radio Frequency (RF), Microwave, Infra Red (IR) etc. Electromagnetic Spectrum is a limited resource and its usage is regulated regulated.

ƒ

ƒ

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RF / Wireless Basics

Wireless Transmission Pass P band

Base Band (Mux/ Demux)

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Wireless Channel (RF / MW)

Pass P band

Radio Modem (TRX)

Radio Modem (TRX)

Carrier

Carrier

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Base Band (Mux/ Demux)

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Antennas and Propagation

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Antennas and Propagation Antenna Basics ƒ Antenna is a part of Transmitting or Receiving system; Provides efficient coupling between Space & Tx O/P or Rx I/P. ƒ It radiates or receives Electromagnetic waves; It redistributes energy, increasing it in some direction than in the other; Compared with fictitious Isotropic Antenna. ƒ Evolution E l ti off Half H lf Wave W Dipole Di l from f open circuited, i it d enlarged l d / bent b t and resonant Transmission Line with Figure of “8” bi-directional Radiation Pattern due to Standing Waves. p ƒ Non resonant Antennas with matched Transmission Line produces unidirectional Radiation Pattern. ƒ Folded Dipole has similar Radiation Pattern as straight Dipole, but with higher I/P Impedance & greater Bandwidth.

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Antennas and Propagation p g Antenna Basics ƒ There is no real gain; Directive Gain compared to that in an omni directional antenna. ƒ Major/main lobe: The radiation lobe containing the direction of maximum radiation. Antenna Pattern

-10db

0db

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Specifications • 20 db gain: in 0 0 direction; 100 times more energy in 0o than an omni directional antenna. • 0 db gain: in 120 0 direction; Same as omni antenna at 120 0 direction. 0 th 20db • -10 db gain: in 180 direction; 1/10 energy in 180 0 direction compared to omni. • Front to Back ratio: 30 db. db SC

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A t Antennas and dP Propagation ti Antenna Specifications p ƒ Half-power beam width: In a radiation pattern, the angle between the two directions in which the radiation intensity is oneh lf the half th maximum i value. l ƒ VSWR: Voltage Standing Wave Ratio ƒ Frequency bandwidth: Operating range of frequencies over which the performance conforms to a specified standard.

ƒ Antenna Types & Examples: ƒ Dipole, Omni directional Antenna for Central Station / Broadcast, Directional Yagi Antenna for Remote Station / TV Receiver, GSM Sectoral Antenna at BTS Site,, Parabolic Reflector at Microwave Tower,, DTH Dish Antenna, Loop, Horn, Helical Antennas etc. March 2006

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Antennas and Propagation p g RF Propagation Modes MF: Ground / Surface Wave HF: Sky Wave; Frequencies below Critical frequency / MUF reflected by Ionospheric layers (D,E,F) VHF / UHF : Direct Wave ( Line Of Sight - LOS) / Ground Reflected Wave / Scattered Wave Microwave: LOS / Repeater / Troposcatter / Satcom Infra Red: Fiber Optics / Free Space Optics (FSO) March 2006

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RF Propagation Wireless Transmission / Reception Pass band

Base Band (Mux/ Demux))

March 2006

Wireless Channel (RF / MW)

Pass band

Radio Modem (TRX)

Radio Modem (TRX)

C i Carrier

C i Carrier SC

Base Band (Mux/ Demux))

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RF Propagation P ti RF Communication Link Analysis / Free Space Path Loss (LOS) Received Power =

GT GR P ((4 π r/λ ) 2

where „ GT is transmit antenna gain in direction of receiver „ GR is i received i d antenna t gain i in i direction di ti off transmitter t itt „ P is transmit power „ r is distance between transmit and received antenna „ λ is wavelength of communication

ƒ

Received Signal Level = TX Power + Net Gains – Net Losses

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RF Propagation Link Power Budget Tx power = 2 W (33 dbm) at 2 GHz ; Tx and Rx antenna gain = 10 db

c 3 × 10 8 m/sec λ= = = 0.15m 9 f 2 × 10 Hz

⎛ 4π ⎞ ⎜ ⎟ ⎝ λ ⎠

2

⎡ 4 × 3.1415 ⎤ = ⎢ ⎥⎦ 0.15 ⎣

2

= 7017

ƒ Power Received at 1m from Transmit Antenna =

33 dbm db + 10 db Tx power

Tx antenna gain

+ 10db - 38db Rx antenna gain

⎛ 4π ⎞ ⎜ ⎟ ⎝ λ ⎠

= 15 dbm db

2

factor

ƒ Power at 10 km from f Tx = -65 6 dbm; Power at 40 km ffrom Tx = -77 dbm. ƒ Free Space Path Loss (LOS) = Effective Tx Power – Rx Power = 130 db. ƒ Free Space Path Loss & Fading (Signal fluctuations at Receiver) due to Multipath Propagation considered for channel modeling. modeling ƒ Fade Margin = RX Level – Threshold Level (Rx Sensitivity) March 2006

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SIGNALLING, SWITCHING & TRANSMISSION

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Signalling, Switching & Transmission

Key Processes in a Telecom Network

ƒ Signalling: Required for establishing, monitoring & releasing a call.

ƒ Switching (Circuit Switching): Subscriber Lines switched to dedicated circuits (Trunks) (Trunks).

ƒ Transmission / Reception over Media ¾ Modulation

/ Demodulation (Analog / Digital)

¾ Multiplexing ¾ Media March 2006

/ Demultiplexing (FDM/ TDM)

Conversion (RF / Optical) SC

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Signalling Signalling Si lli is i usedd to convey Control C t l and d Add Addressing i messages between the Subscriber & Exchange as well as between the Exchanges. Signalling Types „ Subscriber Signalling: g g Signalling g g from subscriber to exchange „

„

Control Signalling / Addressing Signalling

Trunk Signalling: Signalling i lli between b exchanges h Channel Associated Signalling: Line / Register Signalling „ Common Channel Signalling (SS7) „

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Signalling SIGNALLING

Subscriber S b ib - Exchange E h Signalling

Control (DT, RT, BT)

IInter t Exchange E h Signalling

Addressing (DTMF)

Channel Associated Signalling g g (CAS)

Line Signalling •R2 March 2006

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Common Channel Signalling (CCS) • SS7

Register Signalling • MF 47

Subscriber Signalling g g

Exchange

A

B

Hook Off Dialling Tone

425 Hz B Number Ring Back Tone

Ringing Signal B Answer Conversation H kO Hook On

Hook On March 2006

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P l di Pulse dialling lli Address signalling (Decadic) „ „ „

Digits sent as interruption of DC loop 10 interruptions / sec at the ratio of 1:2 make / break Interdigital pause of 200 ms

0.33 T Make

0.67 T Break

Interdigital gap

for Digit 3 March 2006

digit 2 SC

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DTMF Signalling DTMF (Dual Tone Multi Frequency) uses in in-band band Signalling. Signalling Voice band (0.3 - 3.4 kHz) is used. Combination of two frequencies:

1209 1336 1477 1633 (Hz)

697

1

2

3

A

40-50 msec - ON

770

4

5

6

B

40 msec

852

7

8

9

C

941

*

0

#

D

- OFF

DTMF is i highly hi hl reliable li bl and d ffastt Speech will rarely produce two frequencies with similar power DTMF can be employed during conversation - IVRS March 2006

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Signalling Between Exchanges

Exchange

A

Exchange Seizure

B

Seizure Ack

BN Number b Add Address Answer Conversation Clear Back Clear Forward March 2006

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Signalling Between Exchanges Trunks interconnect exchanges & Trunk signalling is carried over these trunks Subscriber lines are almost universal while trunks are of many y types yp Subscriber signalling involves only one link at each end Exchange signalling invariably involves multiple links; setting up a call i involves l many exchanges h serially i ll Link by Link Signalling: Call set up is done by a step by step method Compatibility between exchanges from different suppliers & trunk types critical complex nature of signalling between exchanges March 2006

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Channel Associated Signalling

Channel

CAS: In band & Out of Band March 2006

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Common Channel Signalling SS7 Network Components p

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Common Channel Signalling SS7 Network SCP SCP

SCP STP

A Link

SCP

STP B Link

S S P

A Link STP

STP B Link

S S P

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S S P

S S P

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Outdoor Line connections Overhead telephone lines

Drop p wire

Pillars Distribution cable

Subscriber S b ib premises

Switch

Secondary S d cable

Primary cable Cable chamber March 2006

Cabinets SC

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Switching Switch Technology

ƒ

Evolution:

ƒ Manual M l ƒ Step by Step Electromechanical (Strowger) ƒ Crossbar ƒ Electronic Exchanges ƒStored Program Control (SPC) Digital Exchanges

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Switching

Switching Systems Manual

Automatic

Electromechanical Strowger

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Crossbar

Stored program control Space division

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Time division

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Strowger switching system The components are „ „ „

Relays Uniselectors Two motion selectors - Group and Final selectors

The principle of operation „ „ „ „

operated by subscriber’s dial pulses follows decimal system connection is made at each stage for the caller the last two digits select the called subscriber number and gives the connection

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Strowger switching system

Line relays

Line relays 1stt stage GS 0 9 . .

Final selector l t 0 9 . .

1

1 March 2006

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2nd stage GS 0 9 . . 1

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C b switching it hi system t Crossbar Works on the principle of XY coordinate matrix 1 2 3 4 5 6 7 8 A B C D E F March 2006

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SPC Digital Exchange Space & Time Switching Memory

‘p’ Line

Switch

Memory

Time Slot ‘i’

Time Slot ‘j’

‘q’ Line

Computer

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SPC Digital Exchange ƒ Switching & Subscriber services controlled by Computers with special software. ƒ Time Slot Switching using Memory; Memory stores input PCM samples and reads them out at different time slots of different streams. streams ƒ Switch matrix puts PCM word occurring in slot ‘i’ of any y input p stream ‘p’ p into slot ‘j’ j of any y output p stream ‘q’.

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Numbering plan ƒ

International plan: Country code

1-3 digits

•

Country code

+ National number 9-11 digits

Max = 12 as per ITU

: World divided into 9 zones N. America : 1xx, Africa : 2xx S. America : 5xx, S. Asia : 9xx etc.

•

e.g. India

: 91, Srilanka : 941

Dialling Procedure: ⇒ 0 prefix fi for f national i l calls, ll 00 for f international i i l calls ll

first 0 makes LE route call to TAX, second 0 goes to TAX which routes calls to International Gateway Exchange

ƒ

National number: Access code + Exchange code + Line number March 2006

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Transmission in Telephone Network

Kolkata Mumbai

New Delhi

T Transmission i i link li k Transmission network Trunk automatic exchange

Bangalore

Chennai

T d Tandem exchange h Local exchange March 2006

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Typical Microwave Transmission Link

Terminal station A

Repeater station Terminal station B

Terminal station A To subscribers

Central office ( Telephone exchange )

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Terminal station B Repeater station

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Central office ( Telephone exchange )

To subscribers

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Regenerative Repeater

RF

Down converter

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IF

BB

Demodulator

Pulse restoration

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BB

Modulator

IF

RF

UP converter

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Transmission Transmission / Reception ƒ Modulation „

„ „

„

Technique q for super-imposing p p g voice / data / video message signals on a carrier signal for long distance communication. Analog / Digital Conversion of Signal forms.

Demodulation ƒ Reverse Process to recover the original signal at the receiving end.

Modem: Modulator – Demodulator March 2006

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T Transmission i i Modem Types: Line Modem & Radio Modem ƒ Line Modem Types: Dial-Up Modem, DSL Modem, Cable Modem etc. Dial Up Modem Dial-Up

Dial-up Di l Modem

Internet

TP

PSTN

Copper

Copper

DCE

ƒ ƒ

TP

Dial-up Modem

DCE

DTE DTE DTE: Data Terminal Equipment; DCE: Data Communication Equipment DCE Standards: ITU ‘V’ V Series Standards (Example: V.34, V 34 V.90 V 90 etc) cover Type of Modulation, Data rate etc. March 2006

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Modulation Modulation Message signal (Baseband signal) is low frequency signal. Difficult to transmit low frequency signal over long distances. „

Antenna required is too large, since antenna dimensions are proportional ti l to t ¼ wavelength. l th

„

For 1 KHz, Wavelength = 300 KMs; ¼ Wavelength = 75 KMs KMs.

Modulation enables frequency shifting of baseband signals to high carrier frequencies. March 2006

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Modulation T Types off Modulation M d l ti (Analog (A l & Digital) Di it l) For achieving Modulation, the Amplitude or Frequency or Ph Phase off the th carrier i signal i l is i varied i d proportional ti l to t the th message signal, which can be Analog or Digital. Amplitude Modulation (AM) Vary the amplitude of the Carrier Signal in proportion to the message signal

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Modulation Amplitude Modulation (AM)

Message Signal, em = Em Sin ωmt Carrier Signal, g

ec = Ec Sin ωct

AM Signal, eam = (Ec + Em Sin ωmt) Sin ωct Double Sideband AM (DSB-AM)

ƒ ƒ ƒ ƒ March 2006

e

Carrier amplitude, Ec is proportional to m. AM signal envelope is the message signal itself + dc ((which can be filtered out). ) AM signal in frequency domain has two Sidebands (USB & LSB). Modulation Index = Em / Ec. Application: Radio Broadcast. AM signal is affected by noise & fading. SC

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Modulation EC Amplitude Modulation

LSB

USB

DSB – AM: „ „ „

fc - f m fc fc+f m Typical and Commonly used. Bandwidth = 2* f m, where message bandwidth = f m U Upper sideband id b d (USB) & Lower L sideband id b d (LSB) duplicate d li t information. i f ti

Single Side Band AM (SSB-AM): „ „ „ „

Balanced Modulator suppresses the carrier; Filter removes one side band. SSB Bandwidth = f m Requires pilot transmission; coherent detection. Application: FDM; AM Carrier Communication.

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Modulation

F Frequency Modulation M d l ti (FM) Vary the frequency of carrier signal proportional to message signal. FM Signal, g

efm = Ec Sin (ωc + Em Sin ωmt)t has infinite sidebands.

Transmission BW ~ 2 (fd+fm), where fd is frequency deviation & fm is the message frequency; Modulation Index = m = fd / fm. Typically yp y for wideband FM,, ‘m’ could be 5 ⇒ BW = 12* fm. „ Much higher BW compared to AM (more sidebands than AM). Demodulation by differentiating received signal (Discrimination detection) or Coherent detection (using Phase Lock Loop). Application: FM Radio;TV Sound Broadcast (Picture on AM vestigial sideband & Sound on FM); FM Carrier Communication of FDM Baseband.

Phase Modulation (PM): Vary the phase of carrier signal proportional to message signal; similar to FM. March 2006

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Di it l M d l ti Digital Modulation Modulation Mod lation of carrier signal by b digital bit stream. stream „ Amplitude or Frequency or Phase of the carrier signal is varied by the binary bits “1”and “0”. „ Designated respectively as Amplitude Shift Keying (ASK) or Frequency Shift Keying (FSK) or Phase Shift Keying (PSK). „ Multilevel (M-ary) y) Modulation: Binary y bits ggrouped p into multilevel symbols. Choice of Digital Modulation Scheme „

To provide T id minimum i i Bandwidth B d idth ( hi high hS Spectral t l Effi Efficiency), i ) llow BER BER, good performance in Multipath / Fading conditions, Pulse Shaping, Less Complexity and Cost effectiveness.

PSK & m-ary PSK popular l due d to severall advantages. d March 2006

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Digital Modulation Amplitude Shift Keying (ASK) Or On-Off Keying Baseband Data

1

0

0

1

Carrier Signal

Modulated Carrier signal

ƒ Affected by noise & fading. March 2006

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Di it l M Digital Modulation d l ti Frequency Shift Keying (FSK) Baseband Data

1

0

0

1

Carrier Signal (fc )

BFSK Modulated signal

f0 f0 f1 f1 where f0 = A cos(ωc- Δω)t & f1 = A cos(ωc+ Δω)t; fd = 22*Δf Δf

ƒ M-ary FSK scheme employs multiple frequencies as different states. March 2006

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Di it l M Digital Modulation d l ti Quadrature Phase Shift Keying (QPSK) sin 2πfct

× ×

×

× ×

× decision boundaries

cos 2πfct

×

×

Four modulation symbols with 2 bits per symbol (00, 01, 11 & 10). Can transmit twice as many bits per symbol : bandwidth efficient Symbol Rate = Baud Rate = ½ Bit Rate QPSK has twice the bandwidth efficiency of BPSK, since 2 bits are transmitted in a single symbol. CDMA Mobile System uses QPSK. March 2006

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Digital g Modulation

RRC = Root Raised Cosine Pulse shaping. March 2006

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Digital Modulation QPSK

Offset QPSK (OQPSK)

• All Phase shifts limited to 90 degrees, degrees by just introducing 1 bit delay in Q channel only before modulation. March 2006

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Digital g Modulation Minimum Shift Keying y g (MSK) ( ) ƒ MSK is a form of FSK with Modulation Index of 0.5, resulting in minimum frequency separation. ƒ Half cycle sinusoid pulse shaping results in smooth phase change. change

Gaussian MSK (GMSK) ƒ MSK modulation with Gaussian Pulse shaping. shaping ƒ GSM & DECT Mobile systems use GMSK.

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Digital Modulation 8 - PSK

16 - PSK

ƒ Symbol Spacing is reduced

ƒ Used U d iin EDGE M Mobile bil System S t March 2006

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Di it l M Digital Modulation d l ti 16 QAM (16 - Quadrature Amplitude Modulation) Constellation Diagram Q

×

×

×

×

×

×

×

×

×

×

×

×

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Four Bits per Symbol „ Separation one third of the same in × QPSK for same peak power, P „ Four bits transmitted per symbol × and hence more bandwidth I efficient. × „ Symbol Rate = Baud Rate = ¼ Bit Decision boundary Rate. for each symbol × „ Transmission BW = ½ QPSK BW. SC

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Digital Modulation Pulse Modulation „ „ „ „ „ „ „ „

Pulse Amplitude Modulation (PAM) Pulse Width Modulation (PWM) Pulse Position Modulation (PPM) Pulse Code Modulation (PCM) Differential Pulse Code Modulation (DPCM) Adaptive Differential Pulse Code Modulation (ADPCM) Delta Modulation (DM) Ad ti Delta Adaptive D lt Modulation M d l ti (ADM)

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Digital Modulation Pulse Code Modulation Analog Signal

Band Limiting Filter (4 KHz)

Sampling

Quantization and Coding

Digital Signal (64 Kbps)

– Analog to Digital Conversion – Pulse Code Modulation (PCM) Codecs in Electronic Exchanges.

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Digital Modulation

Pulse Code Modulation Steps Sample band limited speech signal as per Nyquist theorem (@ twice the max. signal i l frequency f off 4 KHz) KH ) for f proper reconstruction t ti off original i i l signal i l att receiver; Under sampling leads to aliasing and loss of information. Nonlinear Quantization as per A-Law (European) or µ Law (North American) Companding; Process introduces Quantization noise. noise Encode each sample by 8 bits (256 levels). 4 KHz Band limited speech p signal g sampled p @ 8000 samples p per p second (every ( y 125 µsec) and encoded by 8 bits / sample

⇒ 64 Kbps per voice channel, designated as E0 signal (European) or Digital Signal 0 (DS0-North (DS0 North American) Standard. March 2006

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Multiplexing p g Multiplexing Combining multiple signals of a multichannel system to share the same communication medium. medium 1 2

1, 2 ...n Mux

De-Mux

n

1 2 n

De-Multiplexing

ƒ

Reverse Process to recover the original signals at the receiving end. March 2006

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Multiplexing p g

Types of Multiplexing

ƒ Analog: Frequency Division Multiplexing (FDM) − different

message signals use different Carrier frequencies.

ƒ Digital: Time Division Multiplexing (TDM) - different message signals use different Time slots.

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Multiplexing Frequency q y Division Multiplexing p g ((FDM))

Signal g A Signal B Signal C

Simultaneous transmission of 3 signals in 1 channel M U L T I P L E X E R

Analog Baseband f T for Transmission i i

D E M U L T I P L E X E R

Signal g A Signal B Signal C

Example:

ƒ One Voice channel = 4KHz (300 Hz to 3400 Hz) ƒ Analog Base band for 12 channel Basic FDM Group = 60 to 108 KHz (Using SSB-AM); 60 / 300 Channels Super Groups. March 2006

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Analog Radio Link

Voice Data Video

Frequency Division Multiplexer

IF

Frequency Modulator

BB

RF

Mixer

RF stage

Local Oscillator RF

RF stage

Mixer

IF

Frequency F Demodulator

BB

Frequency q y Division Demultiplexer

Voice D t Data Video

Local Oscillator March 2006

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Di it l M Digital Multiplexing lti l i Time Division Multiplexing (TDM) Signal A

Signal B

Signal C

M U L T I P L E X E R

Aggregate (interleaved) signal over one communications link

Digital Baseband for Transmission

ƒ 4 KHz Band limited Voice Signal digitized to

Signal A D E M U L T I P L E X E R

Signal B

Signal C

64 Kbps data (E 0 Signal) by

Pulse Code Modulation. ƒ In PCM Primary Mux, Mux 30 digitized voice channel samples are byte interleaved to form E 1 Frame with a Digital Baseband of 2048 Kbps. March 2006

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Digital Multiplexing PCM Primaryy Mux or E1 Mux ((G703))

ƒ

30 digitized Voice channel samples are interleaved to form the E 1 Frame with Digital Baseband of 2.048 Mbps (2 Mbps approx); Frame contains 32 Time Slots including Data Data, Alignment & Signalling information information. 125 μ sec / 256 bits Sl Slot

⇒

0

1

2

• • • • • 31

256 bits in a frame divided in 32 slots of 8 bits each. Bit rate = 256 × 8000 = 32 × 64,000

= 2.048 Mbps

ƒ E1 (European I Order) Mux Digital Baseband = 2.048 Mbps. March 2006

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Digital Multiplexing E1 (30 Channel) Frame Slot 0 is the Marker slot Used U d ffor Frame F Ali Alignment. Slots 1-15 and 17-31 contain the 30 channel samples of 64 Kbps each. „ Each channel slot contains a PCM Word of 64 Kbps data. Slot 16 is meant for Signalling information of 2 Channels per frame. „

Signalling for other channels accommodated in the Multiframe (16 Frames). March 2006

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Digital Multiplexing

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Digital Multiplexing

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Digital Multiplexing ƒ Higher Hi h O Order d M Multiplexing l i l i forms f Plesiochronous Pl i h Digital Di i l Hierarchy Hi h (PDH). (PDH) European Second Order PDH MUX (E 2 MUX) E1 E1 E1 E1

> > > >

E2 MUX

4 x 2.048 +++ (overheads) ≈ 8.448 Mbps = E 2 Base band

22.048 048 Mb Mbps each

Four E1 streams bit-multiplexed to form E2 Baseband (second order PDH), which caters for 120 voice channels channels. Tx bit rate higher than 4 x 2.048 Mbps due to addition of Control, stuff and marker bits. Each input p data stream has its own clock;; Each data stream undergoes g bitstuffing to allow for its clock variation (Plesiochronous Operation). March 2006

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Digital Multiplexing PDH - Third Order Mux (E 3 Mux) Four second order E2 PDH bit-streams combine to form E3 (third order PDH) bit-stream. E3 = 4 E2 = 16 E1 Channels. E 3 Baseband B b d = 34.368 34 368 Mbps Mb (C (Caters t for f 480 channels). h l)

PDH - Fourth Order (E 4) Mux Four input E3 (34 Mbps) streams combined to form E4 Baseband = 140 Mbps (139.264 Mbps) output. E4 = 4 E3 =16 E2 = 64 E1 Channels. March 2006

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Digital Multiplexing T1 ((24 Channel)) Primaryy Mux North American / Japanese I Order PDH. T1 frame is constructed with 24 channel Time Slots (8 Bits each) plus 1 Frame alignment bit added to them. them Each Channel Time Slot occupies 64 kbps bandwidth. Frame length of 125 m Sec contains 193 bits (24*8 + 1). 125 μ sec / 193 bits Fr. Bit

1

2

• • • • • 24

Slot

ƒ

Signalling information is accommodated in the Channel Time slots of 6th, 12th frame etc in the Multiframe.

ƒ T 1 Baseband = (193 / 125) Mbps = 11.544 544 Mbps ƒ T 2 = 4 * T 1; T 3 = 7 * T 2 March 2006

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Digital Radio Link

Voice Data Vid Video

Time Division M lti l Multiplexer

BB

PSK or QAM Modulator

IF

RF

Mixer

RF stage

Local Oscillator RF stage

Mixer

RF

IF

PSK or QAM Demodulator

BB

BB

Regenerator

Time Division Demultiplexer

Voice Data Video

Local Oscillator March 2006

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Digital Multiplexing PDH Limitations Three Regional g ((NA,, Europe p & Japan) p ) Hierarchies with different formats, rates & interfaces existing; Interworking became difficult. Each Multiplexing section has to add overhead bits g rate > more overhead)) for jjustification;; ((higher „ Justification (bit stuffing) spreads data over the frame

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Digital Multiplexing PDH Limitations To Drop / Insert / Cross Connect lower level channels from , say, y, 140 Mbps p E4 Channel,, the composite p stream must be demultiplexed to its constituent streams step by step; The streams must then be remultiplexed to E4 back ; Hence, PDH is not flexible and also is expensive. p E1s

E4

E4

E4 Step by Step demux / remux

E1s

Step by Step demux / remux

Lack of sufficient Network Management functions for Performance monitoring etc. March 2006

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Digital Multiplexing g p g

Synchronous Transmission (SONET / SDH) Overcomes limitations of PDH Network mentioned earlier andd introduces i t d many new features. f t All Equipments synchronized to the Network Clock. ANSI defined Synchronous Optical Network (SONET) for use in US. ITU standardized on Synchronous Digital Hierarchy (SDH) for worldwide usage. SDH & SONET Traffic Interworking is compatible.

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Optical Networking p g SDH Defines G 707 / 708 / 709 standards for Bit Rates, Network Node Interface & Structure respectively. Basic Transmission Rate defined as 155.520 Mbps (155 Mbps) and refereed to as STM-1 ( Synchronous Transport Module 1) Module-1). Higher Transmission rates STM-4 (622.080 Mbps), STM-16 (2488.320 Mbps), etc (STM-N) achieved by straightforward “Byte Interleaving”. SDH Mux structure defined such that STM-1signal can accommodate lower PDH data rates (1.5 (1 5 Mbps to 140 Mbps). Mbps) March 2006

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Optical Networking

SONET Significant differences between SDH & SONET occur at the sub STM 1 level. sub-STM-1 level First level of SONET hierarchy is referred to as Synchronous p Signal-1 g ((STS-1 for an electrical signal) g ) Transport Or Optical Carrier-1 (OC-1 for an optical signal) STS-1 / OC-1 corresponds to a bit rate of 51.84 Mbps. STS-3 / OC-3 signal corresponds to STM-1 (155.52 Mbps). March 2006

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O ti l N t ki Optical Networking Ad Advantages t /A Applications li ti off SDH SDH offers higher Transmission rates, which suits deployment of broadband Fiber Optic Networks. Networks Offers more efficient Add / Drop / Cross connect functions. Incorporates powerful Network Management functions, which are Software controllable. „ Network Planning, Configuration Management, Fault Management, Performance Management, Security Management & Accounting Management functions. „ Enables easy identification of link / node failures and centralized maintenance. maintenance March 2006

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O ti l N t ki Optical Networking Advantages Ad antages / Applications of SDH Wide variety of Interfaces to accommodate PDH / SDH tributaries as well as signals from other networks such as ISDN, ATM, LAN / IP etc. Offers several output Transmission rates and can be duplicated for protection. p Performs Multiplexing and Line Terminating functions. Allows dynamic allocation of bandwidth. Vendor independent equipments could be integrated. SDH is a simplified, reliable and global Network, capable of y g large g message g traffic such as Trunk & Backbone carrying networks. March 2006

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Optical Networking STM-1 Frame 9

125 μsec frame „

9

STM-1 frame

o v e r h e a d

Payload 270

270 x 9 bytes x 64 Kbps = STM 1 Pointer and stuff byte

Payload floats in SDH frame (envelop). Pointer byte points to start of payload. „ can be dropped and inserted easily March 2006

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Optical Networking

„

„

Wavelength Division Multiplexing (WDM): WDM system enables single fiber to carry multiple high speed data streams with carrier frequencies in the order of 200 THz ((1500 nm)) to 300 THz (1000 ( nm). ) By using Fused biconic tapered couplers, multiple wavelength signals are combined on same fiber. Tx

Tx T

1

N

1

W D M

1

...

N

W D M

N

Rx

Rx

Due to fiber attenuation, periodic regeneration was done; New generation Erbium Doped Fiber Amplifiers (EDFA) enable high highspeed, long distance repeater less transmission. „

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Optical Networking Wavelength Demultiplexing Using an optical filter as illustrated in figure

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Optical Networking

CWDM – Coarse Wavelength Division Multiplexing ƒ Number of Wavelengths: g 4 / 8 / 16

ƒ Channel Spacing: > 200 GHz (corresponds to 1.6 nm over the usable spectrum)

ƒ Applications: Cost effective Metro Access & Enterprise networks.

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Optical Networking

DWDM – Dense Wavelength Division Multiplexing As Laser and Optical Filter Technologies improved, more signal i l wavelengths l th could ld be b combined bi d on a single i l fiber. fib ITU has specified DWDM Band in the 1525 to 1565 nm range with su w suitable beC Channel e Sp Spacing c g. Number of Wavelengths: 32 / 40 / 80 / 100 Channel Spacing: p g 200 / 100 / 50 GHz ((corresponding p g to 1.6 nm / 0.8 nm / 0.4 nm over the usable spectrum) Applications: High Capacity long haul (multiple sections of 100 KMs) backbone networks etc. etc March 2006

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