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Topic 9: Wireless Networks - Chapter 13: Wireless Networks Business Data Communications, 4e, William Stallings Wireless LAN vs. WAN Wireless LAN Local area Built by the organization using the LAN WAN Wide area Built on exiting wireless communication networks

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Topic 9: Wireless Networks - Chapter 13: Wireless Networks

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topic 9 wireless networks chapter 13 wireless networks

Topic 9: Wireless Networks- Chapter 13: Wireless Networks

Business Data Communications, 4e,

William Stallings

wireless lan vs wan
Wireless LAN vs. WAN
  • Wireless LAN
    • Local area
    • Built by the organization using the LAN
  • WAN
    • Wide area
    • Built on exiting wireless communication networks
    • Allows cellular phone access to Internet services
cellular revolution
Cellular Revolution
  • In 1990 mobile phone users populate 11 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
reasons for wireless networks
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.
problems with wireless networks
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.
major cellular phone companies in the us
Major Cellular Phone Companies in the US
  • Sprint PCS wireless service
  • AT&T
  • Cellular One
  • Verizon
  • Cingular
  • GTE
mobile telephony
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.
amps components
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
  • Spectral allocation in North America
    • 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
    • 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.

Frequency Reuse

A Seven-Cell Cluster

Space-division multiplexing (SDM):

using the same spectral band in two

physically disjoint places




global system for mobile communication
Global System for Mobile Communication
  • Developed to provide common 2nd-generation technology for 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)
gsm layout
GSM Layout


Mobile Service Switching Center (MSSC)

HLR: home location register database VLR: visitor location register

AuC: authentication center EIR: equipment identity register database

multiple access
Multiple Access
  • Four ways to divide the spectrum among active users
    • frequency-division multiplexing (FDM)
    • time-division multiplexing (TDM)
    • code-division multiplexing (CDM)
    • space-division multiplexing (SDM)
choice of access methods
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
    • 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 third-generation systems
third generation systems
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 multimedia, data, and video
  • Personal communications services (PCSs) and personal communication networks (PCNs) are objectives for third-generation 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
wireless application protocol wap
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:
    • WWW Programming Model
    • Wireless markup language (WML)
    • Specification of a small browser
    • A lightweight communications protocol stack
    • A framework for wireless telephony applications (WTAs)
wap protocols
*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).
wap protocols23
*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.
wap protocols24
*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.
wap protocols25
*WAP Protocols
  • WDP (Wireless Datagram Protocol)
    • 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

WML Wireless Markup Language

  • Tag-based browsing language:
    • Screen management (text, images)
    • Data input (text, selection lists, etc.)
    • Hyperlinks & navigation support
  • XML-based language
  • Inherits technology from HTML

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

A WML Example




<GO URL="#card2"/>


Acme Inc.<BR/>Directory


<CARD NAME="card2">


<GO URL="?send=$type"/>



<SELECT KEY="type">







Acme Inc.






2 Phone

3 Fax




simple object access protocol soap
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.
  • 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.
soap and mobile applications
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.
soap example request
*SOAP Example: Request



<xmlns:m= "" />   


<m:BookName>Fast Food





soap example response
*SOAP Example: Response



<xmlns:m="" />






soap example error
*SOAP Example: Error



<faulstring>Unknown book</faultstring>


soap structure
Envelope contains



Header is optional

Out-of-band information such as…

Authentication information

Message routes


Transaction flow

Body contains XML body of RPC call

*SOAP Structure
soap example 2
*SOAP Example 2

<?xml version="1.0" encoding="UTF-8" ?>

<env:Envelope xmlns:env="">









<m:alert xmlns:m="">

<m:msg>Pick up Mary at school at 2pm</m:msg>




values and references
*Values and References
  • By value - Add([in] int a, [in] int b);
  • By reference - Square([in, out] int &a);

<m:Add xmlns:m=“”>

<a xsi:type=“integer”>3</a>

<b xsi:type=“integer”>4</b>


<m:Add xmlns:m=“”>

<a href=“#arg” />


<a id=“arg” xsi:type=“integer”>8</a>

  • Arrays

int a[3] = {1, 2, 3};

b = Add([in]a);

<m:Add xmlns:m=“”


<a SOAP-ENC:arrayType=“xsd:int[3]”>






soap over http request
*SOAP over HTTP (Request)



Accept: text/*

Content-type: text/xml

Content-length: nnnn

SOAPAction: “”






<t:transId xmlns:t=“”>1234</t:transId>



<m:Add xmlns:m=“”>

<a xsi:type=“integer”>3</a>

<b xsi:type=“integer”>4</b>





*SOAP over HTTP (Response)

HTTP/1.0 200 OK

Content-type: text/xml

Content-length: nnnn






<t:transId xmlns:t=“”>1234</t:transId>



<m:AddResponse xmlns:m=“”>

<c xsi:type=“integer”>7</c>




geostationary satellites
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.
advantages of geostationary orbits
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
problems with geostationary orbits
Problems withGeostationary 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.
leo and meo orbits
LEO and MEO Orbits
  • Alternatives to geostationary orbits
  • LEO: Low earth orbiting (320-1100 Km)
    • Stronger signals
    • Propagation time is smaller
    • Coverage can be better localized
    • Needs more satellites (66 for Iridium system)
  • MEO: Medium earth orbiting (>10,000Km)
types of leos
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
iridium a 3 rd generation satellite system
Iridium: A 3rd Generation Satellite System
  • 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