Chapter 13 Wireless Networks

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Chapter 13 Wireless Networks Powered By Docstoc
					Topic 9: Wireless Networks
- Chapter 13: Wireless Networks

Business Data Communications,
4e,
William Stallings



                                  1
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




                                                      2
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
                                               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


                                                       9
AMPS
 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.


                                                                        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
    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 database
                                                                             14
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)



                                              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
      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

                                                                       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
    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

                                                                               17
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)
                                                                         18
The WAP Architecture


Client                                         Web Server
                    WAP Gateway
 WML




                                                         with WML-Script
                                                CGI
                     WML Encoder




                                                           WML Decks
 WML-                                          Scripts
          WSP/WTP     WMLScript
                                        HTTP    etc.
 Script
                       Compiler
 WTAI
                    Protocol Adapters          Content
  Etc.


                                                              19
WAP Protocol Stack




                     20
Comparison between Internet
and WAP Models
             Wireless Application Protocol

  HTML                  Wireless Application          Other Services and
JavaScript              Environment (WAE)                Applications

                          Session Layer (WSP)
  HTTP
                          Transaction Layer (WTP)


 TLS - SSL                Security Layer (WTLS)

                         Transport Layer (WDP)
  TCP/IP
  UDP/IP     Bearers:
              SMS       USSD   CSD   IS-136    CDMA   CDPD PDC-P    Etc..

                                                                      21
*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).


                                                       22
*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.
                                                          23
*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.

                                             24
*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

                                                  25
Wireless Telephony
Applications




                     26
                 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


                                                 27
                 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


                                              28
   A WML Example
<WML>
    <CARD>
        <DO TYPE="ACCEPT" LABEL="Next">
            <GO URL="#card2"/>
        </DO>                                     Acme Inc.
        Acme Inc.<BR/>Directory                    Directory
    </CARD>                                     _____________
                                                     Next
    <CARD NAME="card2">
        <DO TYPE="ACCEPT">
            <GO URL="?send=$type"/>
        </DO>
        Services
        <SELECT KEY="type">                        Services
            <OPTION VALUE="em">Email</OPTION>      1>Email
            <OPTION VALUE="ph">Phone</OPTION>      2 Phone
            <OPTION VALUE="fx">Fax</OPTION>        3 Fax
        </SELECT>                                ____________
    </CARD>                                           OK
</WML>


      Demon
                                                           29
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.



                                                     30
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.
                                                    31
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.

                                                              32
*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>



                                          33
*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>


                                       34
*SOAP Example: Error
<soap:Fault>
    <faultcode>0x800700E</faultcode>
    <faulstring>Unknown
  book</faultstring>
</soap:Fault>




                                       35
*SOAP Structure
                   Envelope contains
                        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
                                               36
*SOAP Example 2
<?xml version="1.0" encoding="UTF-8" ?>
<env:Envelope xmlns:env="http://www.w3.org/2001/09/soap-
   envelope">
   <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>



                                                           37
*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>



                                                 38
*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>




                                                            39
  *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>                                            40
   *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>


                                                               41
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.

                                        42
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)
     Stronger signals
     Propagation time is smaller
     Coverage can be better localized
     Needs more satellites (66 for Iridium system)
 MEO: Medium earth orbiting (>10,000Km)


                                                      45
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
Iridium: A     Generation
                     3rd

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


                                                              48

				
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