modern telecommunications

8/8/2019 Modern Telecommunications

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Chapter 6

Modern Telecommunications

Systems


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Introduction

Telematique the integration of

computers and telecommunications

systems Computers are changing roles from

computing machines into communications

machines


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Telecommunications

The science and technology of

communication by electronic transmission

of impulses through telegraphy, cable,telephony, radio, or television either with

or without physical media

Tele is Greek for distance

Communicate has its roots in the Latin

word to impart


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Voice Networks

Interactive - Bidirectional networks that

provide on-demand communication

The first telephone networks weredeployed widely following World WarII

By the late 1950s in the United States,

telephones were a permanent fixture in

most homes


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Circuit Switched Networks

Telephone networks use circuit switching

that creates a complete, dedicated, end to

end connection before voice data beginsto flow

Circuit creation results in exclusive

allocation of specific data transmission

resources for the duration of the call


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Circuit Switching

Guarantees that each successful

connection owns all the resources

necessary to deliver a high quality link When the call ends, the circuit is torn

down, and the resources are freed; these

resources can then be utilized for a new

connection


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Switched Network

It is the capacity of the network to

interconnect any two endpoints


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Legacy

The telephone network is one of the

largest legacy systems ever created and

maintained

Phone handsets over 50 years old can still

interoperate seamlessly with current

equipment

Some basic design specifications date

back to the early 1900s


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Telephone Signals

Original telephone specifications were

based on analog signal technology

Analog signals vary in amplitude (signalstrength) and in frequency (pitch)

The telephone handset converts sound

into continuously varying electrical signals

with the microphone

The speaker at the other end converts

electrical signals back to sound


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Analog Signal


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Digital Signals

These signals are discrete and

discontinuous

They exist in predetermined states Binary signals are digital signals limited to

only two states, 0 and 1


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Digital Signal


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Multiplexing

Multiplexing is subdividing the physical

media into two or more channels

Telephone lines use frequencymultiplexing to carry both voice and DSL

signals simultaneously

The frequencies between 0 and 4000 Hz

carry voice, and those between 25 kHz

and 1.5 MHz carry DSL


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Digitizing Voice Signals

By converting analog voice signals into a

digital format, voice can then be

processed like other digital data by

computers

The economies of Moores law and

semiconductor economics can be brought

to bear on voice applications


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Pulse Amplitude and Pulse Code

Modification


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Analog to Digital Conversion

Generally a two step process

First, the analog signal is sampled at regular

intervals; measurements taken at these

periods are converted to a discrete value

Second, the discrete values are converted to

a binary format; this is called pulse code

modulation


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Fidelity

Translating a signal from analog to digital

format results in loss of data. By

increasing the number of discrete values

produced per second (sampling more

often) and increasing the range of discrete

values produced by sampling, the digitized

waveform more closely represents theanalog original. This is fidelity.


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Nyquists Theorem

A mathematical formula that will quantify

the fidelity of the signal given the rate and

resolution of sampling

For a 4000 Hz signal, fidelity will be

acceptable if the signal is sampled 8000

times per second with a resolution of 8 bits

per sample

A 4000 Hz signal is equivalent to a 64000

bit per second data stream


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The Digital Telephone

When a voice signal enters the local

switch, it is digitized

The local switch is located physically closeto the end users of the telephone line

(usually within 10000 ft)

The switch is capable of handling 500 to

1000 copper lines

It is connected via high speed digital links

back to the central office


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Central Office

Handles the telephone traffic for a number

of small communities or a small city

Commonly central offices are responsiblefor 100000 lines


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Central Office Network

Configuration


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Customer Premise Equipment

CPE is the device found at the customer

termination of a telephone connection (fax,

telephone, modem, etc.)


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Local Loop

Also known as the access line

Identified by the last four digits of the

telephone number It is the physical connection between the

CPE and the local switch

The first three digits of a seven digittelephone number identify the local switch

to the central office


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Local Switch

A local switch is a smart router. It can

independently connect calls from any two

lines terminating directly into it.

This helps to keep local calls confined to the

local switch

It identifies and routes outbound calls

quickly to the central office


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Topology

Topology is the configuration of elementsin a network

The local exchange (local switch and allattached CPE and trunks) form a switchedstar network

This is an effective arrangement when

most of the lines are idle at any one time At peak hours 15% of a given set of lines

are in use


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Regional Connections

A Central Office is connected to other

Central Offices by high speed links; it also

has connections to other higher level

centers and long distance networks

These links in the US form a network of

150 million lines


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Regional Telephone Switching

Networks


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Call Setup

When the handset is raised, the local

switch issues a dial tone

When the user inputs the destinationphone number, the local exchange uses it

to set up the circuit

A leading 1 signals the local switch that

the call is long distance and routes the call

immediately to the Central Office


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T-Services

T-services are high speed digital links

using time-division multiplexing (TDM) to

move multiple signals

TDM successively allocates time

segments on a transmission medium to

different users

It combines multiple low speed streams

into one high speed stream


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T-1

The T-1 line is capable of carrying 1.544

Mbps

The T-1 frame is composed of 24 timeslices. Each time slice is a channel. Each

channel is capable of carrying one phone

circuit.


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Time-Division Multiplexing and the

T-1 Frame


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T-1 Frame

Multiplexing equipment aggregates the

incoming individual channels and

constructs a frame

Each channel can transmit 8 bits per

frame

Each frame contains 24 channels and one

framing or start bit

8000 frames are transmitted per second

yielding 1.544 Mbps


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The T-Service Hierarchy

The T-1 connection is composed of 24

channels called B channels

They are able to carry the digitized audiodata for one voice circuit

A T-1 connection can carry 24 Bs

A T-3 connection can carry 672 Bs (45Mbps)


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T-Services


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E-Services

Europeans use a slightly different standard

called the E series

8000 frames per second with each framecomposed of 32 channels

Only 30 of the channels can be used for

data, the other two are reserved for

signaling information and signaling the

framing start sequence

Carries 2.048 Mbps


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Corporate Use of T-Services

T-services are available to customers

T-lines can be configured to create a high

speed private point-to-point network Internally, data and voice can be mixed, so

that a T-1 line can be provisioned to carry

12 voice circuits and 12 data circuits

T-1s allow rapid connection of fixed

locations with high speed private links


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Data Communication Networks

Voice networks have hard requirements

for network latency (the amount of time

needed for data to move from one end to

the other)

Data that arrives late or out of order is

worthless

Pure data networks have looser time

constraints opening the door to different

topologies and technologies


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Packet Switching

In traditional voice networks, circuits are

established that provide for a continuous

stream of data; packet switching takes

outgoing data and aggregates it into

segments called packets

Packets carry up to 1500 bytes at a time

Packets have a header prepended onto

the front of the packet that contains the

destination address and sequence number


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Packet Routing

In circuit switched networks, the entire

data pathway is created before data

transmission commences; in packet

networks, the packet travels from router to

router across the network

At each router, the next hop is chosen,

slowly advancing the packet toward itsdestination


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Packet Routing

Given moment to moment changes in

network loading and connections, packets

may or may not take the same route

In taking different routes, packets may

arrive in a different order than the order

they were transmitted

The destination uses the sequence

number in the header to reassemble the

incoming data in the correct order


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Local Area Networking

Until the 1990s, local area networking

used vendor specific protocols that made

interoperability difficult

With widespread deployment of personal

computers, networking to the desktop

became more imperative for companies,

so that they could fully leverage theirITinfrastructure investments


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Metcalfes Law

Robert Metcalfe is the patent holder for

Ethernet networking

He asserted that the value of a networkincreases as a square function to the

number of attached nodes


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OSI Model

OSI was the Open System Interconnection

model that attempted to modularize and

compartmentalize networking interfaces

The result was a seven layer model

As data passes down from layer 7 to layer

1 it is broken into smaller pieces and

encapsulated with wrappers of additional

information used at the corresponding

layer by the recipient to reconstruct the

original data and destination


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Open System Interconnection

Model


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OSI is a Model

OSI was intended to be the final structure

and framework for global networking

Widespread implementation of the entireOSI model has never taken place

It took years to develop

It was the product of a committee

It was extremely rigid


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ARPANET

In the early 1970s, the Department of

Defense saw the need to make

heterogeneous networks of information

systems communicate seamlessly

They needed networks that were self

healing and had a distributed intelligence

ARPA (Advanced Research Projects

Agency) took the OSI layering concept

and built an operational system with layers

3, 4, and 5 only


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The Internet

From this nucleus of networked machines

grew the Internet

AR

PA called the OSI

layer 4 protocol TCP(Transmission Control Protocol) and layer

3 IP (Internet Protocol), hence the Internet

networking standard TCP/IP

This has become the de facto global

standard, and OSI has been relegated to a

reference model


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Internetworking Technology

The Internet Protocol Suite is a group of

helper applications that standardizes

interactions between systems and assists

users in navigating the Internet

These helper applications work at many

different levels of the OSI model from

seven all the way down to two


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Internet Protocol Suite

Layer seven applications include

FTP File Transfer Protocol

HTTP HyperText Transfer Protocol

SMTP Simple Mail Transfer Protocol

Layer two protocols include

ARP Address Resolution Protocol


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DNS

Domain Name System

A distributed database that contains the

mappings between IP numbers and human

readable naming

DNS is also a Internet Protocol Suite helper

application

D

NS takes a request forwww.yahoo.com andreturns the corresponding IP address


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Domain Names

Composed of a hierarchical naming

database

Moves from general to specific in a right toleft manner

The rightmost element of the name is

called the Top Level Domain (TLD)

TLDs can be country codes, organizations

(.org), commercial (.com), and others


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Communication Between Networks

Layers 1 and 2 are used for the

transmission of data packets between

routers

Layer 1 The Physical Layer

Specifies voltage parameters, timing signaling

rates, and cable specifications

Layer 2 The Data Link Layer Describes how data is formatted for

transmission across a specific type of

Physical Layer link


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Physical Layer Technologies

Transmission links can be built using

either conducting or radiating media

Conducting media create a direct physical

connection between network components like

copper wire or fiber optics

Radiating media uses radio waves to link

stations together


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10 Base T

The most common Ethernet based wiring

standard

Uses 8 stranded wire links

These wires are similar in size to

telephone wire and use slightly larger

modular plugs

Carries data signals at 10 Mbps to 1000

Mbps over distances up to several

hundred meters


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Coaxial Cable

Useful to carry signals over distances up

to several miles

Diameter of coax ranges from 1/4th inch to

one inch

Inner wire surrounded by a foam insulator,

wrapped by a metal shield and covered

with an external insulator


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Coaxial Cable Construction


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Optical-Fiber Media

Used in new installations instead of coax

Capable of carrying extremely high rates

of data over distances exceeding 100

miles

Constructed of a glass core covered with

plastic cladding and bundled with a tough

external sheath


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Construction of Optical-Fiber Cable


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Transmission Modes

Multimode uses internal reflectivity of the

cladding to propagate the signal down the

fiber

Graded Index the glasss refractive index

varies from the center to the edge, causing

the light to bend back toward the center

Single Mode no reflection or refraction,light travels down the center of the fiber

like a wave guide


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Wavelength Division Multiplexing

Multiple different data streams are sent at

the same time down the same fiber. Each

stream is on a distinct color of light.

A wavelength is also called a lambda

Multiplexing hundreds or thousands of

wavelengths down a single fiber is called

Dense Wavelength Division Multiplexing(DWDM)


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Advanced Fiber Transport

Due to low installation costs and high data

capacity, optical fiber is the medium of

choice for new buildings

Fiber has the flexibility to carry voice, data,

and video with no change to the installed

fiber base


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FDDI

OSI layer 1 and 2 specification

Used when building high speed redundant

metropolitan area data networks

Employs two unidirectional rings so that

any cable cut can be healed by looping

data back onto the other ring


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FDDI Network Configuration


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SONET

Synchronized Optical NETwork

Set of standard rates for high speed data

transmission

STS stands for Synchronous Transport

Signal (SONET over copper)

OC stands for Optical Connection (SONET

over fiber)

STS-1 and OC-1 rates are identical


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OC Line Rates


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OC-1 SONET Framing

A SONET frame is made up of a 9 bit x 90

byte block of data (6,480 bits total)

The frame rate is 8000 per second yielding

a data rate of 51.84 Mbps

For higher OC or STS levels, the frame

rate is multiplied by the trailing number

(i.e. OC-3 is 8000 x 3, OC-12 is 8000 x 12)


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Frame Relay, ATM, and Gig-E

These technologies represent newer

frame based networking standards that

are able to deliver high speed, low latency

connections

Use frame-based protocols and star

topologies


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ATM Cells and Frame Relay

Packets


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The Last Mile

High speed global networks are of little

value if individual access is unavailable

WANs terminate locally at POPs (Points of

Presence)

For businesses, T-1 connections are a

common solution to the last mile; T-1s are

expensive to setup and require long termcontracts


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Digital Subscriber Lines

DSL enables regional phone providers to

deliver digital connectivity to customers

over existing copper connections

At the local switch, an additional network

unit is installed called a DSLAM (Digital

Subscriber Local Access Multiplexer)

The DSLAM injects and extracts the DSLinformation into the copper line


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DSL

On the customer side, a modem/router is

attached to the line, injecting and

extracting the DSL signals

DSL connections from the customer to the

local switch is limited to 3.5 miles

80% of phone subscribers in the US are

currently within these boundaries


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Digital Cable

60% of US homes and businesses are

accessible to cable broadcasters

Cable initially was designed for one way

content delivery

In the 1990s, systems were upgraded to

deliver interactive programming and digital

data access


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Digital Cable

The highest margin, fastest growth sector

of the cable industry is cable-based

Internet access

Cable providers piggyback a 5 10 Mbps

digital backbone onto existing broadcast

spectrum

Home users attach specially constructedCable Modems (routers) to interface

home systems to the cable data feed


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Voice Over Cable

Cable operators want to bundle more

services for customers

Delivery of telephone connectivity over

cable systems is an additional service they

can provide

This service will require additional capital

outlays to provision customers at a timewhen growth at any cost is not a viable

business strategy


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Wireless Systems

Licensed wireless Includes cellular voice

and data networks

Unlicensed wireless ad hoc networking

technologies like 802.11b and 802.11g

Both these technologies enable

consumers to have untethered, mobile

connectivity bringing networking to theconsumer instead of making the consumer

find the network


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Licensed Wireless

Cellular service first began in the early

1980s

It has grown at a 30% compounded rate

over the last decade with penetration of

50% across the US

Cellular systems are dense networks of

low power broadband radio transmittersand receivers


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Cellular Network Architecture


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Cellular Standards

1 G Systems

AMPS Advanced Mobile Phone System

2 G Systems

CDMA Code Division Multiple Access

TDMA Time Division Multiple Access

GSM Global System for Mobile

Communications

3 G

W-CDMA

IMT-2000


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Unlicensed Wireless

802.11.b An Ethernet networking

standard that replaces layers 1 and 2 with

a wireless equivalent

11 Mbps network connectivity over a 50m

radius

No transmitter license is necessary so it is

inexpensive for consumers with little setupor administration costs


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Summary

Advances in semiconductor technology

have enabled enormous advances in

telecommunications systems

Rapid change is occurring in this field, and

seems set to change how individuals and

organizations grow, act, and react

modern telecommunications

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