Ch3

Mobile Computing

Chapter 3
Mobile Computing through Telephony
Asoke K Talukder
Hasan Ahmed
© Tata McGraw Hill

Evolution of Telephony
 1876 – First telephone system by Alexander Graham Bell
 1892 – Strowger switch installed as first automatic telephone
exchange
 1960 – Electronic Switching System (ESS) developed by AT&T
 1962 – Carrier system went digital
 1960’s and 1970’s – Stored program telephone exchanges
 1980’s – Wireless telephony emerged
 1990’s – Mobile telephony flourished commercially across the
world

Public Switched Telephone Network
 Three categories of nodes – local exchanges, transit exchanges,
and international exchanges.
 Local exchanges are used for subscriber connection.
 Transit exchanges switch traffic within and between different
geographical areas.
 International exchanges switch traffic to telecommunication
networks in foreign countries and other distant networks.
 Last mile – a physical wire (also known as local loop) that is
laid from local exchange to the device at subscriber premises.
 Last mile is absent in case of GSM or Will network.

Multiple Access Procedures

 We need to control simultaneous access of radio channel in
order to avoid collisions.
 In a connection oriented communication, collisions are
undesirable.
 For effective utilization, channel has to be utilized intelligently
by the use of multiplexing.
 Four major types of multiple access procedures are Frequency
Division Multiple Access (FDMA), Time Division Multiple
Access (TDMA), Code Division Multiple Access (CDMA) and
Space Division Multiple Access (SDMA).

Frequency Division Multiple Access

 The available frequency band is divided into channels of equal
bandwidth so that each communication is carried on a different
frequency.
 FDMA was used in all the first generation analog mobile
networks like TACS in UK and AMPS in USA.

Time Division Multiple Access

 It needs precise synchronization between transmitter and
receiver.
 The whole frequency bandwidth is subdivided into sub – bands
using FDMA techniques. TDMA is then used in each of these
sub – bands to offer multiple access.
 TDMA is more expensive than FDMA.
 GSM uses TDMA.

Code Division Multiple Access

 CDMA uses spread spectrum technique where each subscriber
uses the whole system bandwidth.
 In CDMA, all subscribers in a cell use the same frequency
band simultaneously.
 To separate the signals in CDMA, each subscriber is assigned
an orthogonal code called chip.
 CDMA is a broadband system.

Space Division Multiple Access

 SDMA is a technique where we use different part of the space
for multiplexing.
 SDMA is used in radio transmission and is more useful in
satellite communications to optimize the use of radio spectrum by
using directional properties of antennas.
 In SDMA, antennas are highly bidirectional while allowing
duplicate frequencies to be used at the same time for multiple
surface zones on Earth.
 SDMA requires careful choice of zones for each transmitter
and also requires precise antenna alignment.

Satellite Communication Systems

 Every communications satellite involves the transmission of
information from an originating ground station to the satellite
followed by a retransmission of the information from the satellite
back to the ground called the uplink and the downlink
respectively. Hence, the satellite must have a receiver with receive
antennas, and a transmitter with transmit antennas.

 It must also have some methods for connecting the uplink to
the downlink for retransmission with amplification; also, it must
have electrical power through solar energy to run all of the
electronics. The downlink may either be to a select number of
ground stations or may be broadcast to everyone over a large area.

 A properly designed satellite antenna will concentrate most of
the transmitter power within a designated area using space
division multiplexing.

 One of the biggest differences between a low earth satellite and
a geosynchronous satellite is in their antennas. All antennas in use
today radiate energy preferentially in some direction.

 The most important application for communication satellites
was in intercontinental long distance telephony. The fixed Public
Switched Telephone Network relays telephone calls from land line
telephones to an earth station, where they are then transmitted to a
geostationary satellite.

 The downlink follows an analogous path.

Low Earth Orbit Satellite

 A Low Earth Orbit (LEO) satellite typically orbits around the
earth about 400 kilometers above the earth’s surface with a time
period of about 90 minutes.

 These satellites are only visible from within a radius of roughly
1000 kilometers from the sub-satellite point. Sub-satellite point is
the point of intersection of earth’s surface with the straight line
from the satellite to the center of earth.

 The greatest advantage of LEO satellite is that it does not need
high powered rockets—making it less expensive to launch. Also,
due to its proximity to the ground, LEO does not require high
signal strength.

Medium Earth Orbit Satellite

 A Medium Earth Orbit (MEO), sometimes called Intermediate
Circular Orbit (ICO), is the region of space around the earth above
low earth orbit of 2,000 kilometres and below geostationary orbit
of 35,786 kilometers.

 The most common use for satellites in this region is for
navigation, such as the GPS (with an altitude of 20,200
kilometers), Communications satellites that cover the North and
South Pole are also put in MEO.

 The orbital periods of MEO satellites range from about 2 to 24
hours. The MEO orbit has a moderate number of satellites.

Geostationary Earth Orbit Satellite

 In geostationary satellite, the orbit of the artificial satellite is
such that the orbital speed of the satellite is same as the speed of
earth’s rotation. Though the satellite is moving at a high speed,
from earth it will always appear to be stationary—this is the
reason for calling it geo-stationary.

 The GEO satellite could view approximately 42% of the earth.
Therefore, a system of three GEO satellites, with the ability to
relay messages from one GEO to the other could interconnect
virtually all of the earth except the polar regions.

Satellite Phones

 Initially satellite communication was being used for broadcast
to stationary TV receivers, and transmission of telephone
channels.

 However, demand on mobile phone made some companies to
look into satellite phones that will connect a subscriber directly
through the communication satellite, where the satellite will
function as the transceiver station connecting the mobile phone.

Satellite Phone Companies

 Iridium
 Globalstar
 Thuraya

Mobile Computing through Telephone

 Computer Telephony Interface (CTI) – accessing applications
through voice interface
 Intelligent Networks (IN) – solving problem of multiple and
geographically bounded numbers
 CTI achieved through Interactive Voice Response Service
(IVRS)
 IVRS – known as Voice Response Unit in USA
 Audiotex systems – systems based on IVRS and VRU
 Dual Tone Multi Frequency (DTMF) – extensively used in IVRS

Architecture for CTI

PSTN
(Telephone
Network)
Content Server

Voice & DTMF as input
Voice as output

Benefits of CTI
 Easy integration with existing telephone and computer systems
irrespective of whether they are state – of – the – art databases or
legacy systems

 Independent of the locale and culture as the same application can
be adapted for other languages very quickly

 Very effective for rural population and senior citizens who are
not computer savvy

 Comprehensive voice – processing capabilities designed
specifically for small, middle and large – size businesses

 Provide customized application development tools that are ideal
for different size and types of businesses

How CTI is different?

 The only difference is User Interface
 Input through DTMF telephone keypad
 Input through rotary telephone
 Input through voice
 Output is always audible sound

Interactive Voice Response Service

IVRS

DATA Dial 6542222

• Pre-recorded voice prompts guide the user
to get the relevant information
• User inputs data using the telephone keypad

• Enterprise E-mail / Data

• Flight related information

• Legacy data

Deployment for IVRS

PSTN
Exchange
Application

Mobile
Exchange
IVRS DATA

Architecture for IVRS

DataBase Application

IVRS API’S Remote Monitoring

Dialogic API

Dialogic Hardware

Telecom
Network

Architecture for IVRS – in general

Dialogic architecture for IVRS
User Application

Global Call API

Call Control Libraries

Other ANAPI I CAPI PDKRT ISDN DM3CC SS7
Dialogic
Libraries

Device Drivers
Operating Systems

Firmware Firmware
Network Network
Interface Interface

Telecom
Network

IVRS enables solutions like …

 Text to speech conversion
 Voice / music messaging
 Inbound and outbound call processing
 Audiotex premium rate services
 Intelligent call directing and routing
 Voice mail
 Billing information and fax on demand.
 Reminder service

IVRS – Interface to exchange

 Physical Interface :
Analog : RJ 11
Digital : 2Mbps E1 interface (75 ohm / 120 ohm)
 Digital Signaling :
ISDN-Primary Rate Interface
R2-MFC
SS#7

Features of IVRS – I

 Touch tone input (DTMF)
 Caller identification detection
 Multiple application hosting
 DNI based application routing
 Out dialing
 Call transfer
 Audio recording
 Text – to – speech conversion

Features of IVRS – II

 CDR
 GUI based remote monitoring
 Call statistics (Web Interface)
 Database access
 Data access through Internet
 Support of standard voice file format (.vox, .wav, etc)

Features of IVRS – III

 Input through
- Telephone keypad
- Rotary dial
- Voice recognition
 Numeric input (avoid alphabetic input)
- Convert numeric input to other types of input through menu
 Alphabetic input can be OK if played back
 Output through
- Synthesized voice
- Text – to - speech

Using IVRS through telephone keys

 Alphabets A, B and C on key 2
 Alphabets C, E and F on key 3
 Alphabets G, H and I on key 4
 Alphabets J, K and L on key 5
 Alphabets M, N and O on key 6
 Alphabets P, Q, R and S on key 7
 Alphabets T, U and V on key 8
 Alphabets W, X, Y and Z on key 9

Using IVRS – DTMF frequencies

1209 Hz 1336Hz 1477Hz

697 Hz 1 2/ABC 3/DEF

770Hz 4/GHI 5/JKL 6/MNO

852 Hz 7/PQRS 8/TUV 9/WXYZ

941 Hz * 0 #

Synthesized Voice

 Prerecorded syllables or part of the response recorded into
separate files and stored in persistent storage

 As and when necessary, these files will be played through
programming logic the way we do convert numeric to text in a
bank cheque

 Example: 123 = one.vox + hundred.vox + twenty.vox +
three.vox
where .vox is pre – recorded voice

Voice driver and API’s

 Used to communicate and control voice hardware on IVRS
system
 Can make calls, answer calls, identify caller, play and record
sound from phone line and detect DTMF signals
 Can tear down a call detect that caller has hung up
 Offers API’s to record transaction details

IVRS Programming

 Voice libraries are supported by Dialogic to interface with
voice driver
 Voice libraries exist for single and multithreaded applications
 C function libraries exist for a number of purposes
 Standard run time library provides a set of common functions
independent of device and applicable to Dialogic devices

Single threaded programming model

 Enables a program to control multiple voice channels within a
single thread
 Allows development of applications where multiple tasks
need to be coordinated simultaneously
 Supports both polled and call back event management

Multithreaded programming model

 Uses functions that block application execution until the
function completes
 Applications control each channel from a separate thread or a
process
 Enables IVRS system to assign distinct applications to different
channels dynamically in real time

Voice API’s

 Dialogic provides API’s to use voice board
 API’s are available for:
- Device management
- Configuration functions
- I/O functions
- Play and record functions
- Tone detection and generation functions
- Call control functions

Dialogic IVRS functions

 dx_open( ) - opens a voice channel
 dx_close( ) - closes a voice channel
 dx_wtcallid( ) - waits for rings and reports Caller ID
 dx_getdig( ) - gets digits from channel digit buffer
 dx_play( ) - plays recorded voice data
 dx_playvox( ) - plays a single .vox file
 dx_playwav( ) - plays a single .wave file
 dx_rec( ) - records voice data
 dx_recvox( ) - records voice data to a single .vox file
 dx_recwav( ) - records voice data to a single .wave file
 dx_dial( ) - dials an ASCII string of digits

IVRS applications – I
 Virtual Receptionist:

Having a hard time finding someone to answer the phones and
route calls? Active call center can answer and screen your phone
calls, take messages, or even route.

 Automated Information Retrieval:

Give yourself more time to deal with important issues. Create
simple touch tone menus that will allow your customers to
retrieve directions, contact information, store hours, special
promotions, and more.

IVRS applications – II
 Interactive Voice Response with content from databases:

Integrate with your databases and deliver retrieved information
back to the caller. For example, a caller might request his order
status by entering their order number via touch – tone.

 Need to send SMS:

With this revolutionary technology, you can send SMS from your
landline phone to any mobile in the world.

IVRS applications – III

 Hands free and eyes free communication
 Voice messaging and voice enabled infotainment services
 Prepaid and calling card call management
 Self configuring systems
 Flight schedules & status
 Voice mail and voice portals
 Telebanking
 Binary downloads
 Songs on request
 Telephone directory
 Call centres

Voice XML

 XML based mark up language for creating distributed voice
applications
 Creates audio dialogs that feature synthesized speech, digitized
audio, spoken voice recognition and DTMF key input
 Helps creation of web based voice applications that users can
access over telephone

Features of Voice XML dialogs

 Spoken input
 DTMF input
 Recording of spoken input
 Synthesized speech output
 Recorded audio output
 Dialog flow control
 Scoping of input

Voice XML in web environment
 Voice server manages several voice browser sessions.
 Each voice browser session includes one instance of voice
browser, speech recognition engine and text – to – speech engine.
 Voice browser renders and interprets Voice XML documents.
 Voice and telephone are needed to access web information and
services over voice browser.
 Voice XML application defines a series of dialogs between user
and computer.
 The user is always in a dialog at any time and each dialog
determines the next dialog to transition to.
Transitions are specified using URI’s.

Essentials of Voice XML

 First line will always contain <?xml> element.
 Second line will always contain <vxml> element.
 Every Voice XML tag <tag> must have a associated </tag>.
 Last line should contain </vxml>.
 Prompts, grammar, form, events and links are building elements
of a Voice XML document.

Prompts in Voice XML

 Information is presented through audio prompts.
 Prompts can be either pre – recorded audio or synthesized
speech.
 <prompt> is used to generate TTS.
 Any text within body of prompt element is spoken.
 The software shall read out ―Would you like coffee, tea, milk or
nothing?‖ in
<prompt> Would you like coffee, tea, milk or nothing </prompt>

Grammar in Voice XML
 Every dialog has one or more speech or DTMF grammars
associated with it.
 <grammar> is used to define what the caller can say to the
application at any given time.
 Three types of grammar are supported: Inline, External and
Built – in.
 Inline grammars are defined right in the Voice XML document.
 External grammars are specified in another file and referenced
from within Voice XML document code.
 Built – in grammars are pre – specified grammars.

Forms in Voice XML

 Forms are a way of developing dialog with the caller.
 A Voice XML form is a process to present information and
gather input from the caller.
 A Voice XML form is a collection of one or more fields that the
caller fills in by saying something.
 Fields tell the caller what to say and define words and phrases
that the caller can say.
 Based on the caller’s input, the application takes an appropriate
action.

Events in Voice XML

 Events is Voice XML is a mechanism to handle situations
thrown by the platform under a variety of circumstances such as
when the user does not respond, requests help, etc.

Links in Voice XML

 Links support a mixed initiative.
 It specifies a grammar that is active whenever the user is in the
scope of the link. If user input matches the link’s grammar, control
transfers to link’s destination URI.
 Links can be used to throw an event to go to a destination URI.

Example of Voice XML document
<?xml version="1.0"?>
<vxml version="1.0">
<form id="add_funds">
<field name="amount" type="currency">
<prompt>How much?</prompt>
</field>
<field>
<prompt>Charge to credit card or tuition
bill?</prompt>
<grammar> credit card | credit | tuition | tuition
bill</grammar>
</field>
</form>
</vxml>

Elements of Voice XML – I
 <assign> Assign a variable a value
 <audio> Play an audio clip within a prompt
 <block> Container of (non – interactive) executable code
 <break> JSML element to insert a pause in output
 <catch> Catches an event
 <choice> Define a menu item
 <clear> Clears one or more form item variables
 <disconnect>Disconnect a session
 <div> JSML elements
 <dtmf> Specify a touch – tone key grammar
 <else> Used in <if> elements
 <elseif> Used in <if> elements
 <emp> JSML element to change speech output

Elements of Voice XML – II
<enumerate> Shorthand for enumerating choices in a menu
<error> Catches an error event
<exit> Exits a session
<field> Declares an input field in a form
<filled> An action executed when fields are filled
<form> Presents information and collects data
<goto> Goes to another dialog
<grammar> Specifies a speech recognition grammar
<help> Catches a help event
<if> Simple conditional logic
<initial> Declares initial logic
<link> Specifies a transition
<menu> Dialog for choosing amongst alternatives
<meta> Defines a meta data item as a name/value pair

Elements of Voice XML – III
<noinput> Catches a no – input event
<nomatch> Catches a no – match event
<object> Interacts with a custom extension
<option> Specifies an option in a <field>
<param> Parameter in <object> or <subdialog>
<prompt> Queues TTS and audio output to the user
<property> Control implementation platform settings
<pros> JSML element to change the prosody of speech
<record> Records an audio sample.
<reprompt> Plays a field prompt when a field is re-visited
<return> Returns from a sub – dialog
<sayas> Modifies how a word or phrase is spoken
<script> Specifies a block of ECMA script
<subdialog> Invokes another dialog as a sub – dialog of the
current one

Elements of Voice XML – IV

<submit> Submit values to a document server
<throw> Throws an event
<transfer> Transfers the caller to another destination
<value> Inserts the value of a expression in a prompt
<var> Declares a variable
<vxml> Top – level element in each Voice XML document

JSpeech Markup Language (JSML)

 JSML defines a specific set of elements to mark up text to be
spoken, and defines the interpretation of those elements so that there
is a common understanding between synthesizers and documents
producers of how marked up text will be spoken.

 JSML elements provide a speech synthesizer with detailed
information on how to 'speak' text and thus, enables improvements in
the quality, naturalness and understandability of synthesized speech
output.

 JSML defines elements that describe the structure of a document,
provide pronunciations of words and phrases, indicate phrasing,
emphasis, pitch and speaking rate, and control other important speech
characteristics.

 JSML is designed to be simple to learn and use, to be portable
across different synthesizers and computing platforms, and to be
applicable to a wide range of languages.

Telephony Application Programming
Interface
 In Telephony Application Programming Interface (TAPI), a
developer can develop voice based services without going too
deep into it.
 Speech Application Programming Interface (SAPI) is also one
such standard.
 The use of available API’s of TAPI and SAPI shall save the
programmer of the pain of trying to program hardware directly.
 TAPI includes interface for convergence of both traditional
PSTN and IP telephony.

Benefits of TAPI

 Simple user interfaces to set up calls
 GUI to set up conference call
 See whom you are talking to
 Make voice attachments with electronic mails
 Users can hear voice attachments when reading mails
 Send and receive faxes
 Set and configure group and security measures

Next Chapter

Emerging Technologies

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