Telecommunications & Networks By Umamaheswari.T

Communication Model Message is communicated via a signal Transmission medium (communication channel) “carries” the signal Feedback Encode Decode

Telecommunications Electronic transmission of signals, e.g., telephone, radio, television Telecommunication medium: Anything that carries an electronic signal & interfaces between a sending device & a receiving device Data Communications: A subset of telecommunications referring to the sending, transmission, & receiving of data -- typically between computer systems

Communications & Telecommunications In human speech, signals are transmitted through the air; in telecommunications, signals are transmitted through various media

Telecommunications Applications (1) Linking computers & data terminals: Download & upload information Voice Mail: Enables users to send, receive, & save verbal messages, including sending the same message to a “group” E-mail: Enables users to send, receive, & save text messages & attached documents Telecommuting: Enables employees to work away from the office using PCs & networks to communicate electronically

Types of telecommunication Media (1) Twisted Pair Insulated copper wire Electrical signals Coaxial Cable Inner wire core surrounded by shielding Higher transmission speeds than twisted pair Fiber-optic Cable Extremely thin strands of glass bound together Light pulse signals Very high transmission speeds

Types of Telecommunication Media (2) Microwave Satellite

Types of Telecommunication Media (3) Cellular transmission signals are transmitted to receivers & integrated into the regular network. Chapter 6 IS for management

Open Wire Transmission Systems

Paired Cable Transmission Systems

Attenuation Vs Frequency

Two Wire Transmission Systems Fig 1.15 shows the single wire transmission used in the past was too noisy for customer acceptance. Fig 1.16 used with signals propagating as a voltage difference between two wires. METALLIC CURRENT The electrical current produced by the difference signal flowing through the wires in opposite direction. LONGITUDENAL or COMMON-MODE CURRENT Current propagating in same direction in both wires

Two Wire to Four Wire Conversion Two-Wire : One path for both directions Old analog end offices were used a two-wire transmission system Four-Wire: Two separate paths for two directions Interoffice trunks typically use four-wire transmission system Derived Four-Wire: Separating the B.W. of single pair into two sub bands

Loaded Coil The usual method to reduce amplitude distortion on intermediate length pairs is to insert an artificial inductance into the lines That can be done by loaded coils.

Frequency Division Multiplexing

A5 Channel Bank Multiplexer

LMX Group Bank Multiplexer

Time Division Multiplexing

T-Carrier Systems The functions of regenerative repeaters 1. Equalization 2. Clock Recovery 3. Pulse Detection 4. Transmission

REGENERATIVE REPEATER

TDM Hierarchy

TDM Hierarchy E1 30 VC –-2.048 E5 30-2.048 E4 1920-M34-8.448

Digital Pair Gain Systems --- Subscriber loop carrier

Subscriber loop multiplexer Chapter 6

Digital Transmission & Multiplexing Selection of a finite set of discrete electrical waveform for encoding the information Defines time relationships between the individual transmission signals The timing information requires channel capacity in terms of B.W. , data rate ,code space.

Pulse Transmission

Inter Symbol Interference Small perturbations in the channel response. Main causes 1. Timing Inaccuracies 2. Insufficient B.W. 3. Amplitude Distortion 4. Phase Distortion

Line Coding Line coding considerations Provides adequate timing information Line coding considerations Spectrum of the line code Available B.W Noise and interference levels Performance monitoring Synchronization acquisition times Implementation Cost

Level Encoding Level Encoding UniPolar Polar BiPolar

Bipolar Coding Solves the dc wander problem by using 3 levels to encode binary data A logic “0” is encoded with 0V A logic “1” is encoded with +ve & -ve voltages The average level can be maintained at level ‘0’ to eliminate dc components in the spectrum. Also called as Alternate Mark Inversion(AMI)

Code Space Redundancy Detects the errors depending on the polarity of successive pulses Same polarity Error Alternate polarity No Error The error is called bipolar violation Inserts bipolar violations to signify TDM Marks, Alarm conditions or Special codes to increase timing information Chapter 6 IS for management

Binary N-Zero Substitution More number of 0’s in a code leads to timing jitter. Replace all strings of N 0’s by a special N-length code BNZS B3ZS B6ZS B8ZS

BINARY 3-ZERO SUBSTITUTION: Each string of 0’s encoded with either 00V or B0V

B6ZS

B8ZS

High Density Bipolar 3 code

Examples 1011010001010010001101 B3ZS: 101101 000 101001 000 1101 Chapter 6 IS for management

Digital Biphase Differential Encoding Also called as Diphase or Manchester. Maintains good timing information No DC wander Complete square wave 1->+ve &-ve ; 0-> opp. phase Differential Encoding

Time Division Multiplexing Synchronous Asynchronous Time Division Multiplexing Assigned a time slot corresponding to a single bit Bit Interleaving Assigned a longer time slot corresponding to some larger no. of bits Word Interleaving

Framing Added Digit Framing Frame synchronisation Added Channel Framing Unique line signal Framing Statistical Framing

Added Channel Framing (DS1)

Added Channel Framing (E1)

TDM LOOPS & RINGS

SONET/SDH

SONET MULTIPLEXER

SONET Frame Formats SONET Layers

STS-1 FRAME Line Overhead Path Overhead Section Overhead

STS-3 Frame Format Chapter 6 IS for management

SONET Overhead Layers

Payload Pointers Chapter 6 IS for management

Virtual Tributaries VT Types