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Topic 9: Wireless Networks - Chapter 13: Wireless Networks


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Title: Topic 9: Wireless Networks - Chapter 13: Wireless Networks

Topic 9 Wireless Networks- Chapter 13 Wireless
  • 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
  • Allows cellular phone access to Internet services

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
  • Mobile communication is needed.
  • Communication must take place in a terrain that
    makes wired communication difficult or
  • A communication system must be deployed quickly.
  • Communication facilities must be installed at low
    initial cost.
  • The same information must be broadcast to many

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
  • Sprint PCS wireless service
  • ATT
  • Cellular One
  • Verizon
  • Cingular
  • GTE

Mobile Telephony
  • First Generation (AMPS)
  • analog voice communication using frequency
  • Second Generation (GSM)
  • digital techniques and time-division multiple
    access (TDMA) or code-division multiple access
  • Third Generation
  • evolving from second-generation wireless systems
  • will integrate services into one set of standards.

Advanced Mobile Phone Service
AMPS Components
  • Mobile Units
  • contains a modem that can switch between many
  • 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
  • The bandwidth has been split into two 12.5 MHz in
    each direction for two operators to compete each
  • 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.

Space-division multiplexing (SDM) using the same
spectral band in two physically disjoint places
West Europe
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
    (935960 MHz), 25 MHz for mobile transmission
    (890915 MHz)

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
  • Four ways to divide the spectrum among active
  • frequency-division multiplexing (FDM)
  • time-division multiplexing (TDM)
  • code-division multiplexing (CDM)
  • space-division multiplexing (SDM)

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,
  • FDM, used in 1st generation systems, wastes
  • 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
  • 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
  • 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)
  • 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
  • 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

The WAP Architecture
WAP Protocol Stack
Comparison between Internet and WAP Models
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 Protocols
  • WTP (Wireless Transaction Protocol)
  • Provide efficient request/reply based transport
    mechanism suitable for devices with limited
    resources over networks with low to medium
  • 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 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 Protocols
  • WDP (Wireless Datagram Protocol)
  • The Transport layer protocol in the WAP
  • 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

Wireless Telephony Applications
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
LABEL"Next"gt ltGO URL"card2"/gt
lt/DOgt Acme Inc.ltBR/gtDirectory
lt/CARDgt ltCARD NAME"card2"gt ltDO
URL"?sendtype"/gt lt/DOgt
Services ltSELECT KEY"type"gt
ltOPTION VALUE"em"gtEmaillt/OPTIONgt
ltOPTION VALUE"ph"gtPhonelt/OPTIONgt
lt/SELECTgt lt/CARDgt lt/WMLgt
Acme Inc. Directory _____________ Next
Services 1gtEmail 2 Phone 3 Fax
____________ OK
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
  • 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
  • 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, SOAPLite, DM's SOAP/Perl and the XMethods
    soap Server.

SOAP Example Request
  • ltsoapEnvelopegt
  • ltsoapBodygt
  • ltxmlnsm "http//" /gt   
  • ltmGetBookPricegt
  • ltmBookNamegtFast Food
  • Nationlt/mBookNamegt  
  •     lt/mGetBookPricegt
  • lt/soapBodygt
  • lt/soapEnvelopegt

SOAP Example Response
  • ltsoapEnvelopegt
  • ltsoapBodygt
  • ltxmlnsm"http//" /gt
  • ltmGetBookPriceResponsegt
  • ltmPricegt34.5lt/mPricegt
  • lt/mGetBookPriceResponsegt
  • lt/soapBodygt
  • lt/soapEnvelopegt

SOAP Example Error
  • ltsoapFaultgt
  • ltfaultcodegt0x800700Elt/faultcodegt
  • ltfaulstringgtUnknown booklt/faultstringgt
  • lt/soapFaultgt

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

SOAP Example 2
  • lt?xml version"1.0" encoding"UTF-8" ?gt
  • ltenvEnvelope xmlnsenv"http//
  • ltenvHeadergt
  • ltnalertcontrol
  • xmlnsn"http//
  • ltnprioritygt1lt/nprioritygt
  • ltnexpiresgt2001-06-22T140000-0500lt/nexpi
  • lt/nalertcontrolgt
  • lt/envHeadergt
  • ltenvBodygt
  • ltmalert xmlnsm"http//"gt
  • ltmmsggtPick up Mary at school at
  • lt/malertgt
  • lt/envBodygt
  • lt/envEnvelopegt

Values and References
  • By value - Add(in int a, in int b)
  • By reference - Square(in, out int a)

ltmAdd xmlnsmhttp//
lta xsitypeintegergt3lt/agt ltb
xsitypeintegergt4lt/bgt lt/mAddgt
ltmAdd xmlnsmhttp//
lta hrefarg /gt lt/mAddgt lta
idarg xsitypeintegergt8lt/agt
  • Arrays

int a3 1, 2, 3 b Add(ina)
ltmAdd xmlnsmhttp//
coding/gt lta SOAP-ENCarrayTypexsdint3gt
ltSOAP-ENCintgt3lt/SOAP-ENCintgt lt/agt lt/mAddgt
SOAP over HTTP (Request)
POST / HTTP/1.0 Host Accept text/ Content-type
text/xml Content-length nnnn SOAPAction
http// CRLF ltSOAP-E
NVEnvelope xmlnsSOAP-ENVhttp//schemas.xml SOAP-ENVencodingStyle
ltSOAP-ENVHeadergt ltttransId
lt/SOAP-ENVHeadergt ltSOAP-ENVBodygt
ltmAdd xmlnsmhttp//
lta xsitypeintegergt3lt/agt ltb
xsitypeintegergt4lt/bgt lt/mAddgt
lt/SOAP-ENVBodygt lt/SOAP-ENVEnvelopegt
SOAP over HTTP (Response)
HTTP/1.0 200 OK Content-type text/xml Content-len
gth nnnn CRLF ltSOAP-ENVEnvelope
velope/ SOAP-ENVencodingStyle"http//schemas
ltSOAP-ENVHeadergt ltttransId
lt/SOAP-ENVHeadergt ltSOAP-ENVBodygt
ltmAddResponse xmlnsmhttp//
ltc xsitypeintegergt7lt/cgt
lt/mAddResponsegt lt/SOAP-ENVBodygt lt/SOAP-ENVEn
Geostationary Satellites
  • Circular orbit 35,838 km above the earths
  • 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
  • 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 withGeostationary Orbits
  • Signal can weaken after traveling gt 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
  • 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 (gt10,000Km)

Satellite Orbits
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
  • Big LEOs Work at frequencies above 1 GHz and
    supporting data rates up to a few megabits per

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