mobile client

7/25/2019 Mobile Client

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Mobile Client and Mobile IP


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CONTENTS Mobile Client

Moving beyond desktop Mobile handset overview

Mobile phones and their features

PDA

Design Constraints in applications for handheld

devices


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CONTENTS MOBILE IP

Introduction Discovery

Registration

Tunneling

Cellular IP

Mobile IP with IPv6


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Client Programming

Introduction ArthurC Clark (1997) quoted information is not

knowledge, knowledge is not wisdom and wisdom is

not foresight. Each grows out of the other and we need

them all

In essence hardware, software and network together make

powerful applications possible, each is not more or less than

theother


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MOVING BEYOND DESKTOP

Handheld devices have evolved Mobile devices have been traditionally classified as phones,

pagers and personal data assistants (PDAs)

Cell phone- used for communication, similar to wired phones

Pagers provides text message

PDAs provide portable data applications like calendar and

notepad

Most cell phones now include address books and SMS, e-mail

access and almost all contemporary PDAs includecommunication capabilities

Today devices offer many permutation and combinations of these

features leading to one-size-fits-all devices


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EVOLUTION OF CELLULAR TECHNOLOGY


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EVOLUTION OF PDA


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COMPARISON OF CAPABILITIES OF DIFFERENT DEVICES


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EVOLUTION OF MOBILE TECHNOLOGY


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SUMMARIZING

All applications thus have basic requirement The least they require is:

Some input to provide some useful output

Memory for runtime and persistent storage

Some communication capabilities

Most of these are device capabilities , but programming

at a device level is cumbersome and generally not

advisable

There is a need for some level of abstraction on thebare hardware this layer of abstraction is the device

operating system


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Palm programming is mostly done in C / C++ Symbian in C++ / Java

WinCE or PocketPC in embedded VB or embedded VC


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STRUCTURE OF A MOBILE DEVICE


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A PEEK UNDER THE HOOD: HARDWARE OVERVIEW

Modern devices have a Million Instructions PerSecond(MIPS) capability to process information stream

(voice/data) stream

Both classes of devices essentially consists of:

A microprocessor A power source

A signal converter

An I/O unit

Some memory (both persistent and volatile)


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Overview of a Digital Communication Device


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MOBILE PHONES


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The above diagram depicts the internal components of a cell phone

Antenna: the signal reception unit

Circuit board: this is the control unit of the system, it has several important chipsmounted on it, the prominent amongst these are:

1.The analog-to-digital and digital-to-analog conversion chips This is represented as RF to Digital block

This is the entry and exit point to the phone

This chip is designed to convert analog network signals to digital for the phone toprocess and reverse

2. The microprocessor

This controls and co-ordinates the handset functions It includes the user input / output and network interfaces that include

communication with the base station

3. The ROM and Flash memory chips provide storage for the phones storagerequirements, which include system memory and application memory

Additional memory is also provided through external detachable memory cards

4. The Digital Signal Processor (DSP) is a highly sophisticated chip that managesthe signal manipulations

5. The radio frequency chip manages the signal channels while the power section isresponsible fro power management and recharging


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Other components are

Display unit is the output, generally a Liquid CrystalDisplay (LCD) panel

Keyboard (qwerty or T): This is the input unit

Microphone: To facilitate speech transmission

Speaker: The microphones listener counter part

Battery: The source of electrical energy


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FEATURES OF MOBILE PHONES

Features Baseband architecture

Processor

Audio / video components

Data storage Display


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Baseband

Functionality is architecturally a larger concept

Helpful in provision of cellular control logic, signal processingand user interface management

Contributes in memory and energy management

Conglomeration of tradeoffs between electromagnetic

capability, performance, power consumption and cost Electromagnetic capability is determined by placement of

high speed circuits and RF transmitter location along withother mechanical constructions

Performance is calibrated in terms of user requirements (likeuser interfaces, mobile phone execution engine etc.),instructions processed per second and other systemrequirements


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Design constraints in Applications for Handheld Devices

Device characteristics: Low-end processors

Small screen size

Cumbersome input device

Limited battery power Memory limitations


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Design Constraint 1: Processing Power

Processing speed starts from 16MHz Some heavy duty computations like encryption key

generation is a drain on the devices resources, thus

needs a good processor design

Offloading the computations to the server is always agood idea, but will leads to poor response, which is

frustrating experience for the user

Too many computations on the client while allowing

for faster response eat into valuable memory


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Categorizing client based on the functionality and

specificity of the software

Thin clients:

Generic, cater to wide range of sources

Similar to web browsers

Communication from the server is mainly based ondifferent flavors of Markup Language(ML)

Requires a local parser The server needs to send large amount of display

information to the client, to adequately represent data,chocking up the transmission channel

Thus the thin client offers generality at the cost of bandwidth

This is a major consideration in networks where the userspay for the data and not call time


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Thick Clients: The intelligence resides in the device and a call is made to

the server only for data

Computation is done locally

While this approach resolves the bandwidth problem but

introduces two major concerns viz., size of the application

on the device and the distribution of the application when

an update of fix happens


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Thin plus or semi-thick clients: These lie somewhere in between thick and thin

Based on the functionality of the application

The bandwidth availability

Cost constraints


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Design Constraint 2: Screen Size:

Handheld device characterized by Small screen size

Limiting information that we can display at one time

Screen should be designed very carefully to fit the small

screen display

Good practice to limit the scrolling to two screens below

Navigation should be easy using a single click

General thumb rule is to consider the depth of the

navigation should be at most four clicks


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Design Constraint 3: Cumbersome Input Devices

Most devices sport stylus or T keypad or very smallqwerty keyboard keying is a pain

Input should be kept to the minimum

Try to device inputs as a single click kind of option like

Yes / No may be substituted by a radio button as scrolland click in most devices is easier than clicking


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Design Constraint 4: Application Load Time

Generally, user switch on their handhelds for shortduration

Eg: Often it is used to retrieve a contact number

The load time for such application should be low as the

user would not like to wait for the application to loadeach time


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Design Constraint 5: Battery

Batteries are scarce resource One of the keys to the success of the application is long

battery life

Sound, extended animations, Serial or IR

communications and many MIME intensiveapplications use CPU for longer period and thus

consume large amounts of power


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Design Constraint 6: Memory

Most of the handheld devices have limited storagespace, ranging from 512MB to 8GB

Dynamic heap ranging from 32K to 256K

Such circumstances optimization is very crucial

The optimization mantra is heap first

speed second

code size third


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Design Constraint 7: Data Storage

All devices provide some amount of persistent storage

This is very limited

Different devices organize data in different ways

Palm OS-based devices

Treat all storage as database blocks


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Design Constraint 8: Backward Compatibility

Devices are rapidly evolving and in very short span of

time the user feel their device a being obsolete

Users are not expected to upgrade their system every

time an advanced version becomes available

So, to gain wider acceptance, there is a need to writeapplications in such a manner that they will run on all

versions of the device

At the same time give the users of a later version better

functionality


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Design Constraint 9: Application Size

Applications need to be stored on the devices

Most devices have limit on the size of executables

This needs to be taken care during the design phase

Should ensure that only absolutely necessary stuffresides on the device


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RECENT DEVELOPMENTS IN CLIENT TECHNOLOGIES

Mobile devices are becoming increasingly popular

Grown upto 3.5 billion by the end of 2009

Dividing line between mobile phones, PDAs or mobilecomputers are slowly disappearing

Host of multimedia features introduced Services and portals having specific affinity to support

these devices are gaining popularity

Several independent service providers catering tovarious sets of use cases

Range of OS like Symbian, Windows Mobile, Samsung'sBada, Palm OS, Blackberry OS, Iphone OS, GooglesAndroid etc.


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MOBILE IP


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INRODUCTION TO MOBILE IP

Mobile computing aids user with continuous access to

data and services in a state of mobility

Mobile Computing vs Portable Computing

Portable Computing

We move with the computing device from one location to another Use network while stationary

Mobile Computing

Offers seamless computing and data networking facility even if the

user is in a state of mobility and changes the network

Handling Mobility Management where a user is at a

vehicular state and accessing the network


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IP and TCP working

IP routes packets from a source endpoint to thedestination endpoint

IP address of a node is a combination of network address and the node address

The network portion of an IP address is used by routers

to deliver the packet to the last router in the chain towhich the target computer is attached

The last router then uses the host portion of the IPaddress to deliver the IP packet to the destination

computer In addition to IP we need TCP / UDP port of the

applications


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Connections scenario

A TCP connection is identified by a quadruplet that contains

the IP address and the port number of the senderendpointalong with the IP address and the port number ofthe receiving endpoint

In case the users are mobile, it is essential that all of these four

identifiers remain constant(physically / virtually) The TCP ports are application specific and thus are generally

constant

IP address will change when a node moves from one subnet toanother

To fix this problem, Mobile IP allows the mobile node to usetwo IP addresses

The IP addresses are called home address and care-of-address


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Home address and Care-of-address

Home address

Original static IP address of the node

Known to everybody as the identity of the node

Care-of-address

Changes at each new point of attachment Is mobile nodes location specific address

These are similar to MSISDN number and the MSRN(Mobile

Station Roaming Number) respectively as in GSM network


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Two more network elements in Mobile IP that play a

very significant role in routing of the packets as part of

mobility management are home agent and foreign

agent

Home agent It is a router on a mobile nodes home network

It forwards datagrams for delivery to the mobile node

through a tunnel when it is away from home

The home agent also maintains current locationinformation of the mobile node


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Foreign Agent

It is a router on a mobile nodes visited network which

provides routing services to the mobile node while registered

The foreign agent detunnels and delivers datagrams to the

mobile node that were tunneled by the mobile nodes home

agent

For datagrams sent by a mobile node, the foreign agent may

serve as a default router for registered mobile nodes

This is similar to the concept of HLR and VLR in cellular

network

Step 1:


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Step 1: When a mobile node is located on its home network, it operates with its

mobility services

Step 2: When the mobile node detects that it has moved to a foreign network,

it registers with the foreign agent and obtains a care-of address on theforeign network

Step 3: The care-of address can either be determined from a foreign agents

advertisement or by some external assignment mechanism like DHCP

Step 4: The mobile node registers its new care-of address with its home agent

informing its new location and new care-of address

Step 5: The home agent forwards all the incoming data packets to the foreign

network using the care-of address

Step6: The delivery requires that the packet header is modified so that the

care-of address becomes its destination IP address


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Step 7:

The new header encapsulates the original packet, causing the

mobile nodes home address to have no impact on the

encapsulated packet routing Diagram depicting how Mobile IP works

The diagram shows

General terms how Mobile IP deals with the problem of

dynamic IP addressesOn returning to its home network from being registered

elsewhere, the mobile node deregisters with its foreign agent,

through exchange of a Registration Request and the

Registration Reply message


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Mobile IP Architecture


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Let us look at the example of IP datagrams being

exchanged over a TCP connection between the mobile

node A and another host Server X, following are the

steps involved: Step 1:

Server X wants to transmit an IP datagram to node A

The home address of A is advertised and known to X

X does not know whether A is in the home network or somewhereelse, thus X sends the packet to A with As home address as the

destination IP address in the IP header

The IP datagram is routed to As home network


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St 3


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Step 3:

At the foreign network, the incoming IP datagram isintercepted by the foreign agent

The foreign agent is the counterpart of the home agent in theforeign network

The foreign agent strips off the outer IP header, and deliversthe original datagram to A

Step 4:

A intends to respond to this message and sends traffic to X In this example X is fixed IP address

For routing As IP datagram to X, each datagram in sent tosome router in the foreign network

This router is the foreign agent A uses Xs static IP address as the destination address in the

IP header

S 5


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Step 5:

The IP datagram from A to X travels directly across the

network using the Xs IP address as the destination address


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Discovery

Agent advertisement is transmitted by both home and

foreign agents to advertise their services on a link

Mobile node uses these advertisements to determinetheir current point of attachment to the Internet

The Mobile IP discovery procedure has been built on

top of existing ICMP (Internet Control MessageProtocol)

router discovery

router advertisement

router solicitation procedure Mobile IP uses control messages that are sent to and

rom UDP port number 434


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Additional ICMP router information includes

0 One-byte Padding

16 Mobility Agent Advertisement

19 Prefix-Length

Mobile IP control messages include extension like 1 Registration Request

3 Registration Reply

32 Mobile-Home Authentication

33 Mobile Foreign Authentication 34 Foreign-Home Authentication


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The discovery process

For discovery

The router or an agent periodically issues a router advertisementICMP message

The mobile mode on receiving the advertisement packetcompares the network portion of the router IP address with thenetwork portion of its own IP address allocated by the home

network If they do no match then the mobile node knows that it is in a

foreign network

What is router advertisement?

A router advertisement can carry information about default router

and one or more care-of address If a mobile node needs a care-of address without waiting for the

agent advertisement, then the mobile node can broadcast asolicitation that will be answered by any foreign agent


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Registration

Once a mobile node obtained a care-of address from

the foreign network, same needs to be registered with

the home agent

The mobile node sends a registration request to a

home agent with the care-of address information When the home agent receives this request, it updates

its routing table and sends a registration reply back to

the mobile node


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Authentication

As part of registration, the mobile node needs to be

authenticated Each mobile node, foreign agent and the home agent

support a mobility security association (SA) for mobileentities

This is indexed by their security parameters index (SPI)and IP address, which must be its Home Address

Registration messages between a mobile node and its homeagent MUST be authenticated with an authorization-enabling extensions

Eg: The Mobile-Home Authentication Extension, this MUST be thefirst authentication extension, foreign agent-specificationextensions MAY be added to the message after the mobile nodecomputes the authentication

The registration process involves the following four


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The registration process involves the following four

steps:

The mobile node requests for forwarding service from the

foreign network by sending a registration request to theforeign agent

The foreign agent relays this registration request to the home

agent of that mobile node

The home agent either accepts or rejects the request and

sends a registration reply to the foreign agent

The foreign agent relays this reply to the mobile node


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Tunneling

In mobile IP, an IP-within-IP encapsulation mechanism

is used

Here the home agent adds a new IP header called the

tunnel header

The new tunnel header uses the mobile nodes care-ofaddress as the tunnel destination IP address

The tunnel source IP address is the home agents IP address

The tunnel header uses 4 as the protocol number

In IP-within-IP, the entire original IP header is preserved sthe first part of the payload of the tunnel header

The foreign agent after receiving the packet, drops the

tunnel header and delivers the rest tit he mobile node


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Tunneling in Mobile IP


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IP header in Mobile IP

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