Topic 9: Wireless Networks
- Chapter 13: Wireless Networks
Business Data Communications,
4e,
William Stallings
1
Wireless LAN vs. WAN
 Wireless LAN

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Local area
Built by the organization using the LAN
 WAN
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Wide area
Built on exiting wireless communication networks
Allows cellular phone access to Internet services
2
Cellular Revolution
 In 1990 mobile phone users populate 11
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million. By 2004 the figure will become 1
billion
Phones are most obvious sign of the success
of wireless technology. Handsets are getting
smaller, lighter, yet more powerful
Service prices are dropping
Service quality are being improved
The applications have expanded from voice
application to Internet applications
3
Reasons for Wireless Networks
 Mobile communication is needed.
 Communication must take place in a terrain that
makes wired communication difficult or impossible.
 A communication system must be deployed quickly.
 Communication facilities must be installed at low
initial cost.
 The same information must be broadcast to many
locations.
4
Problems with Wireless
Networks
 Operates in a less controlled environment, so
is more susceptible to interference, signal
loss, noise, and eavesdropping.
 Generally, wireless facilities have lower data
rates than guided facilities.
 Frequencies can be more easily reused with
guided media than with wireless media.
5
Major Cellular Phone
Companies in the US
 Sprint PCS wireless service
 AT&T
 Cellular One
 Verizon
 Cingular
 GTE
6
Mobile Telephony
 First Generation (AMPS)

analog voice communication using frequency
modulation.
 Second Generation (GSM)

digital techniques and time-division multiple access
(TDMA) or code-division multiple access (CDMA)
 Third Generation


evolving from second-generation wireless systems
will integrate services into one set of standards.
7
Advanced Mobile Phone
Service
8
AMPS Components
 Mobile Units


contains a modem that can switch between many
frequencies
3 identification numbers: electronic serial number,
system ID number, mobile ID number
 Base Transceiver

full-duplex communication with the mobile
 Mobile Switching Center
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AMPS
 Spectral allocation in North America
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Two 25-MHz bands are allocated to AMPS: 869-894 MHz from the
base station to the mobile unit, 824-849 MHz from the mobile unit
to the base station
The bandwidth has been split into two 12.5 MHz in each direction
for two operators to compete each other.
A 12.5 MHz channel allows 416 channels.
 Spatial allocation

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10-50 frequencies are assigned to each cell
Depends on the pattern of cells. Each cell may have N/n
frequencies, where N = 395, and n = 7 is the smallest pattern
Original cells are 6.5-13km in size. 1.5-km is the practical minimum
size. Too small size will have more frequency change.
Transferring from one base transceiver to another is called handoff.
10
A Seven-Cell Cluster
Frequency Reuse
Space-division multiplexing (SDM):
using the same spectral band in two
physically disjoint places
11
West
Europe
12
Global System
for Mobile Communication
 Developed to provide common 2nd-generation technology for
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Europe
200 million customers worldwide, almost 5 million in the North
America
GSM transmission is encrypted, using stream cipher A5 for
transmissions from subscriber to transceiver. A3 is used for
authentication.
It uses subscriber identity module (SIM) in the form of smart
card.
Supports both data and image services based on ISDN model,
with rates up to 9.6 kbps
Spectral allocation: 25 MHz for base transmission (935–960
MHz), 25 MHz for mobile transmission (890–915 MHz)
13
GSM Layout
HLR, VLR, AuC, EIR
Mobile Service Switching Center (MSSC)
HLR: home location register database VLR: visitor location register
AuC: authentication center
EIR: equipment identity register database14
Multiple Access
 Four ways to divide the spectrum
among active users
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frequency-division multiplexing (FDM)
time-division multiplexing (TDM)
code-division multiplexing (CDM)
space-division multiplexing (SDM)
15
Choice of Access Methods
 A random access scheme using FDM, TDM, SDM or CDM to
dynamically assign sub-channels to users is called random
access method, e.g. FDMA, TDMA, CDMA, SDMA.
 FDM, used in 1st generation systems, wastes spectrum
 Debate over TDMA vs CDMA for 2nd generation
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TDMA advocates argue there is more successful experience with
TDMA.
CDMA proponents argue that CDMA offers additional features as
well, such as increased range.
TDMA systems have achieved an early lead in actual
implementations
CDMA seems to be the access method of choice for thirdgeneration systems
16
Third Generation Systems
 IMT-2000 defined the 3rd-generation capacities:

voice quality, 144kbps data rate for high speed mobile, 384 kbps data rate
for low speed mobile, 2.048 Mbps office use, packet/circuit switching,
Internet interface, more efficiency of spectrum use, more mobile equipment
support, flexible for new services and technologies.
 Intended to provide high speed wireless communications for
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multimedia, data, and video
Personal communications services (PCSs) and personal
communication networks (PCNs) are objectives for thirdgeneration wireless.
Planned technology is digital using TDMA or CDMA to provide
efficient spectrum use and high capacity
PCS handsets are designed to be low power, small and light
Future public land mobile telecommunications systems
(FPLMTS) includes both terrestrial and satellite-based services
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Wireless Application Protocol
(WAP)
 A universal, open standard developed by WAP forum to provide
services:

wireless phone, pager, personal digital assistants, Internet, web,
etc.
 It is designed to work with all wireless network technologies
 It is based on Internet standards:

IP, XML, HTML and http
 WAP specification includes:
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WWW Programming Model
Wireless markup language (WML)
Specification of a small browser
A lightweight communications protocol stack
A framework for wireless telephony applications (WTAs)
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The WAP Architecture
Web Server
WAP Gateway
WML
WML Encoder
WMLScript
WSP/WTP
WMLScript
Compiler
HTTP
CGI
Scripts
etc.
WTAI
Protocol Adapters
Content
WML Decks
with WML-Script
Client
Etc.
19
WAP Protocol Stack
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Comparison between Internet
and WAP Models
Wireless Application Protocol
Wireless Application
Environment (WAE)
HTML
JavaScript
Other Services and
Applications
Session Layer (WSP)
HTTP
Transaction Layer (WTP)
Security Layer (WTLS)
TLS - SSL
Transport Layer (WDP)
TCP/IP
UDP/IP
Bearers:
SMS
USSD
CSD
IS-136
CDMA
CDPD PDC-P
Etc..
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*WAP Protocols
 WSP (Wireless Session Protocol)

Provides the application layer of WAP
with a consistent interface for two session
services.
 A connection-oriented service that operates
above the transaction layer protocol WTP.
 A connectionless service that operates above
a secure or non-secure datagram service
(WDP).
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*WAP Protocols
 WTP (Wireless Transaction Protocol)

Provide efficient request/reply based
transport mechanism suitable for devices
with limited resources over networks with
low to medium bandwidth.
 WTP Push mode allows server to “push” data
to a client without request (e.g. notification
of stock hitting target price)
 WTP/WDP uses less than half the packets
that TCP/IP uses to transfer the same
amount of data.
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*WAP Protocols
 WTLS (Wireless Transport Layer
Security)

A security protocol based upon the
industry-standard Transport Layer
Security (TLS) protocol, formerly known
as Secure Sockets Layer (SSL). WTLS is
intended for use with the WAP transport
protocols and has been optimized for use
over narrow-band communication
channels.
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*WAP Protocols
 WDP (Wireless Datagram Protocol)

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
The Transport layer protocol in the WAP
architecture
Provides a common interface to the
Security, Session, and Application layers
Allows these upper layers to function
independently of the underlying wireless
network. This is the key to global
interoperability
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Wireless Telephony
Applications
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WML
Wireless Markup Language
 Tag-based browsing language:
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Screen management (text, images)
Data input (text, selection lists, etc.)
Hyperlinks & navigation support
 XML-based language
 Inherits technology from HTML
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WML
Wireless Markup Language
 Card metaphor
User interactions are split into cards
 Navigation occurs between cards
 Explicit inter-card navigation model
 Hyperlinks
 UI Event handling
 History
 State management and variables
 Reduce network traffic
 Results in better caching

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A WML Example
<WML>
<CARD>
<DO TYPE="ACCEPT" LABEL="Next">
<GO URL="#card2"/>
</DO>
Acme Inc.<BR/>Directory
</CARD>
<CARD NAME="card2">
<DO TYPE="ACCEPT">
<GO URL="?send=$type"/>
</DO>
Services
<SELECT KEY="type">
<OPTION VALUE="em">Email</OPTION>
<OPTION VALUE="ph">Phone</OPTION>
<OPTION VALUE="fx">Fax</OPTION>
</SELECT>
</CARD>
</WML>
Demon
Acme Inc.
Directory
_____________
Next
Services
1>Email
2 Phone
3 Fax
____________
OK
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Simple Object Access Protocol
(SOAP)
 A way for a program running in one kind of OS to
communicate with a program in the same or another
kind of OS by using HTTP and XML as the
mechanisms for information exchange.
 SOAP specifies exactly how to encode an HTTP
header and an XML file so that a program in one
computer can call a program in another computer
and pass it information. It also specifies how the
called program can return a response.
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SOAP
 Developed by Microsoft, DevelopMentor, and
Userland Software and has been proposed as a
standard interface to the Internet Engineering Task
Force (IETF).
 Somewhat similar to the Internet Inter-ORB Protocol
(IIOP), a protocol that is part of the Common Object
Request Broker Architecture (CORBA).
 Program calls are much more likely to get through
firewall servers that screen out requests other than
those for known applications. Since HTTP requests
are usually allowed through firewalls, programs using
SOAP to communicate can be sure that they can
communicate with programs anywhere.
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SOAP and Mobile Applications
 Two recently introduced products available for the Java
2 Micro Edition (J2ME) and Microsoft Windows CE
platforms make XML and SOAP on handheld products a
reality.


The first of these products is the open source kXML parser
for J2ME. kXML is a "pull-based" XML parser, which
basically means that the developer must loop through the
XML document tree to "pull" the necessary elements out.
Also included is support for WBXML parsing and a SOAP
API (to be named kSOAP is in the works).
Another recently announced XML/SOAP tool is PocketSOAP
for Windows CE. PocketSOAP is the result of the efforts of
Simon Fell. According to Simon, the PocketSOAP client can
call other SOAP servers implemented using 4s4c, ROPE,
Apache SOAP, SOAP::Lite, DM's SOAP/Perl and the
XMethods soap Server.
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*SOAP Example: Request
<soap:Envelope>
<soap:Body>
<xmlns:m=
"http://www.amzn.org/books" />
<m:GetBookPrice>
<m:BookName>Fast Food
Nation</m:BookName>
</m:GetBookPrice>
</soap:Body>
</soap:Envelope>
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*SOAP Example: Response
<soap:Envelope>
<soap:Body>
<xmlns:m="http://www.amzn.org/books" />
<m:GetBookPriceResponse>
<m:Price>34.5</m:Price>
</m:GetBookPriceResponse>
</soap:Body>
</soap:Envelope>
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*SOAP Example: Error
<soap:Fault>
<faultcode>0x800700E</faultcode>
<faulstring>Unknown
book</faultstring>
</soap:Fault>
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*SOAP Structure
 Envelope contains

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Header
Body
 Header is optional

Out-of-band information
such as…
 Authentication
information
 Message routes
 Logging
 Transaction flow
 Body contains XML body
of RPC call
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*SOAP Example 2
<?xml version="1.0" encoding="UTF-8" ?>
<env:Envelope xmlns:env="http://www.w3.org/2001/09/soapenvelope">
<env:Header>
<n:alertcontrol
xmlns:n="http://example.org/alertcontrol">
<n:priority>1</n:priority>
<n:expires>2001-06-22T14:00:00-05:00</n:expires>
</n:alertcontrol>
</env:Header>
<env:Body>
<m:alert xmlns:m="http://example.org/alert">
<m:msg>Pick up Mary at school at 2pm</m:msg>
</m:alert>
</env:Body>
</env:Envelope>
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*Values and References
 By value
- Add([in] int a, [in] int b);
<m:Add xmlns:m=“http://a.com/Calculator”>
<a xsi:type=“integer”>3</a>
<b xsi:type=“integer”>4</b>
</m:Add>
 By reference - Square([in, out] int &a);
<m:Add xmlns:m=“http://a.com/Calculator”>
<a href=“#arg” />
</m:Add>
<a id=“arg” xsi:type=“integer”>8</a>
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*Arrays
 Arrays
int a[3] = {1, 2, 3};
b = Add([in]a);
<m:Add xmlns:m=“http://a.com/Calculator”
xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/”>
<a SOAP-ENC:arrayType=“xsd:int[3]”>
<SOAP-ENC:int>1</SOAP-ENC:int>
<SOAP-ENC:int>2</SOAP-ENC:int>
<SOAP-ENC:int>3</SOAP-ENC:int>
</a>
</m:Add>
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*SOAP over HTTP (Request)
POST /Calculator.pl HTTP/1.0
Host: www.a.com
Accept: text/*
Content-type: text/xml
Content-length: nnnn
SOAPAction: “http://www.a.com/Calculator#Add”
{CR}{LF}
<SOAP-ENV:Envelope
xmlns:SOAP-ENV=“http://schemas.xmlsoap.org/soap/envelope/”
SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/”>
<SOAP-ENV:Header>
<t:transId xmlns:t=“http://a.com/trans”>1234</t:transId>
</SOAP-ENV:Header>
<SOAP-ENV:Body>
<m:Add xmlns:m=“http://a.com/Calculator”>
<a xsi:type=“integer”>3</a>
<b xsi:type=“integer”>4</b>
</m:Add>
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>
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*SOAP over HTTP (Response)
HTTP/1.0 200 OK
Content-type: text/xml
Content-length: nnnn
{CR}{LF}
<SOAP-ENV:Envelope
xmlns:SOAP-ENV=“http://schemas.xmlsoap.org/soap/envelope/”
SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/”>
<SOAP-ENV:Header>
<t:transId xmlns:t=“http://a.com/trans”>1234</t:transId>
</SOAP-ENV:Header>
<SOAP-ENV:Body>
<m:AddResponse xmlns:m=“http://a.com/Calculator”>
<c xsi:type=“integer”>7</c>
</m:AddResponse>
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>
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Geostationary Satellites
 Circular orbit 35,838 km above the
earth’s surface
 rotates in the equatorial plane of the
earth at exactly the same angular speed
as the earth
 will remain above the same spot on the
equator as the earth rotates.
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Advantages of
Geostationary Orbits
 Satellite is stationary relative to the earth, so no
frequency changes due to the relative motion of the
satellite and antennas on earth (Doppler effect).
 Tracking of the satellite by its earth stations is
simplified.
 One satellite can communicate with roughly a fourth of
the earth; three satellites separated by 120° cover most
of the inhabited portions of the entire earth excluding
only the areas near the north and south poles
43
Problems with
Geostationary Orbits
 Signal can weaken after traveling > 35,000 km
 Polar regions and the far northern and southern
hemispheres are poorly served
 Even at speed of light, about 300,000 km/sec,
the delay in sending a signal from a point on the
equator beneath the satellite 35,838 km to the
satellite and 35,838 km back is substantial.
44
LEO and MEO Orbits
 Alternatives to geostationary orbits
 LEO: Low earth orbiting (320-1100 Km)

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Stronger signals
Propagation time is smaller
Coverage can be better localized
Needs more satellites (66 for Iridium system)
 MEO: Medium earth orbiting (>10,000Km)
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Satellite Orbits
46
Types of LEOs
 Little LEOs: Intended to work at
communication frequencies below1 GHz
using no more than 5 MHz of bandwidth
and supporting data rates up to 10 kbps
 Big LEOs: Work at frequencies above 1
GHz and supporting data rates up to a
few megabits per second
47
rd
3
Iridium: A
Generation
Satellite System

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66 small LEOs
Services: voice, paging, wireless phone
Proposed in 1987
Put in service 1999
Named for the element iridium because 77 electrons match the
number of satellites
Transmissions between satellites
$5 billion to implement
Motorola 9505 terminal for Iridium weighs about 13 oz. (370g)
2.4 hour talk time, 24 hours standby time
Using L band (1600-1700 MHz) for ground communications and
18-30 GHz between satellites
48