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Topic 9: Wireless Networks- Chapter 13: Wireless Networks

Business Data Communications, 4e, William Stallings

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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

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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

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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.

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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.

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Major Cellular Phone Companies in the US

Sprint PCS wireless serviceAT&TCellular OneVerizonCingularGTE

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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.

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Advanced Mobile Phone Service

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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 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.

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Frequency Reuse

A Seven-Cell Cluster

Space-division multiplexing (SDM):using the same spectral band in two physically disjoint places

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West Europe

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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)

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GSM Layout

Mobile Service Switching Center (MSSC)

HLR, VLR, AuC, EIR

HLR: home location register database VLR: visitor location registerAuC: authentication center EIR: equipment identity register database

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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)

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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

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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

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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:

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

Content

CGIScriptsetc.

WML D

ecks

with

WML-Script

WAP Gateway

WML Encoder

WMLScriptCompiler

Protocol Adapters

Client

WML

WML-Script

WTAI

Etc.

HTTPWSP/WTP

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WAP Protocol Stack

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Comparison between Internet and WAP Models

HTMLJavaScript

HTTP

TLS - SSL

TCP/IPUDP/IP

Wireless Application Protocol

Wireless ApplicationEnvironment (WAE)

Session Layer (WSP)

Security Layer (WTLS)

Transport Layer (WDP)

Other Services andApplications

Transaction Layer (WTP)

SMS USSD CSD IS-136 CDMA CDPD PDC-P Etc..

Bearers:

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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 ProtocolsWTP (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 ProtocolsWTLS (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 ProtocolsWDP (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

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Wireless Telephony Applications

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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

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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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<WML><WML> <CARD><CARD> <DO TYPE="ACCEPT" LABEL="Next"><DO TYPE="ACCEPT" LABEL="Next"> <GO URL="#card2"/><GO URL="#card2"/> </DO></DO> Acme Inc.<BR/>DirectoryAcme Inc.<BR/>Directory </CARD></CARD>

<CARD NAME="card2"><CARD NAME="card2"> <DO TYPE="ACCEPT"> <DO TYPE="ACCEPT"> <GO URL="?send=$type"/><GO URL="?send=$type"/> </DO></DO> ServicesServices <SELECT KEY="type"><SELECT KEY="type"> <OPTION VALUE="em">Email</OPTION><OPTION VALUE="em">Email</OPTION> <OPTION VALUE="ph">Phone</OPTION><OPTION VALUE="ph">Phone</OPTION> <OPTION VALUE="fx">Fax</OPTION><OPTION VALUE="fx">Fax</OPTION> </SELECT></SELECT> </CARD></CARD></WML></WML>

Acme Inc.Directory

_____________Next

Services1>Email 2 Phone3 Fax

____________OK

A WML Example

Demon

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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 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/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>

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*Values and References

By value - Add([in] int a, [in] int b);

By reference - Square([in, out] int &a);

<m:Add xmlns:m=“http://a.com/Calculator”> <a xsi:type=“integer”>3</a> <b xsi:type=“integer”>4</b> </m:Add>

<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

Arraysint 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/1.0Host: www.a.comAccept: text/*Content-type: text/xmlContent-length: nnnnSOAPAction: “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 OKContent-type: text/xmlContent-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

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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.

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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)

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Satellite Orbits

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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

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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