Pages

Ads 468x60px

Labels

Friday, 13 April 2012

ppt on mobile computing


MOBILE COMPUTING


INTRODUCTION

                   What will computers look like in ten years, in the next country?  No wholly accurate prediction can be made, but as a general feature, most computers will certainly be portable.  How will users access networks with the help of computers or other communication devices?  An ever-increasing number without any wires, i.e., wireless. How will people spend much of their time at work, during vacation? Many people will be mobile already one of the key characteristics of today’s society.  Think, for example, of an aircraft with 800 seats.  Modern aircraft already offer limited network access to passengers, and aircraft of the next generation will offer easy Internet access.  In this scenario, a mobile network moving at high sped above ground with a wireless link will be the only means of transporting data to an from passengers.  Furthermore, think of cars with Internet access and billions of embedded processors that have to communicate with for instance cameras, mobile phones, CD-players, headsets, keyboards, intelligent traffic signs and sensors.

                    There are two different kinds of mobility: user mobility and device portability.  User mobility refers to a user who has access to the same or similar telecommunication services at different places, i.e., the user can be mobile, and the services will follow him or her.  Examples for mechanisms supporting user mobility are simple call-forwarding solutions known from the telephone or computer desktops supporting roaming (i.e., the desktop looks the same no matter which computer a user uses to into the network)

                   With device portability the communication device moves (with or without a user).  Many mechanisms in the network and inside the device have to make sure that communication is still possible while it is moving.   A typical example for systems supporting device portability is the mobile phone system, where the system itself hands the device from one radio transmitter (also called a base station) to the next if the signal becomes too weak.  Most of the scenarios described in this book contain both user mobility and device portability at the same time.
 
                    With regard to devices, the term wireless is used.  This only describes the way of accessing a network or other communication partners, i.e., without a wire. The wire is replaced by the transmission of electromagnetic waves through the air (although wireless transmission does not need any medium).

What is Mobile Computing?

                   Mobile Computing and Communications is a major part of wireless communication technology. Mobile communication today is a defector standard by itself.  It commands the single largest share of the Global wireless technologies in the market.  Mobile communications popularity grew many folds over the past few years and is still growing to a greater extent.  Through WAP development of Mobile Computing Applications is becoming easy and affective.  It has also become a foundation for many wireless LAN applications.

APPLICATIONS
         
                   Although wireless networks and mobile communications can be used for many applications.  Some of them are given as follows.

1.Vehicles:  
                    Tomorrow’s cars will comprise many wireless communication systems and mobility aware applications.  Music, news, road conditions, weather reports, and other broadcast information are received via digital audio broadcasting (DAB) with 1.5 Mbits/s.  For personal communication, a global system for mobile communications (GSM) phone might be available offering voice and data connectivity with 384 kbits/s.  For remote areas satellite communication can be used, while the current position of the car is determined via global positioning system (GPS).  Additionally, cars driving in the same area build a local adhoc network  for fast information exchange in emergency situations or to help each other keeping a safe distance.   In case of an accident, not only will the airbag be triggered, but also an emergency call to a service provider informing ambulance and police.  Cars with this technology are already available.  Future cars will also inform other cars about accidents via the ad hoc network to help them slow down in time, even before a driver can recognize the accident.  Buses, trucks, and train are already transmitting maintenance and logistic information to their home base, which helps o improve organization (fleet management), and thus save time and money.

                   GSM, UMTS will be interconnected with trucked radio systems (TETRA) and wireless LANs (WLAN).  Additionally, satellite communication links can be used.  The networks between cars and also inside a car will more likely work in an ad hoc works between cars ad also inside a car will more likely work in an ad hoc fashion. 
Wireless pico networks inside a car can comprise PDAs, laptops, or mobile phones, e.g., connected with each other using the Bluetooth technology.

2. Emergencies:     
                    Just imagine the possibilities of an ambulance with a high quality wireless connection to a hospital.  After an accident, vital information about injured persons can be sent to the hospital immediately.  There, all necessary steps for this particular type of accident can be prepared or further specialists can be consulted for an early diagnosis.  Furthermore,           wireless networks are the only means of communication in the case of natural disasters such as hurricanes or earthquakes.

3.Business
                   Today’s typical traveling salesman needs instant access to the company’s database: to ensure that the files on his or her laptop reflect the actual state, to enable the company to keep track of all activities of their traveling employees, to keep databases consistent etc., with wireless access, the laptop can be turned into a true mobile office.

MOBILE AND WIRELESS DEVICES

                   Currently, laptops are considered to be the upper end of the mobile device range.  Following list gives some examples of  mobile  and wireless devices graded by increasing performance (CPU , Memory , Display , Input devices etc.,) 



Sensor:
                    A very simple wireless device is represented by a sensor transmitting state information.  An example for such a sensor could be a switch sensing the office door.  If the door is closed, the switch transmits this state to the mobile phone inside the office and the mobile phone will not accept incoming calls. Thus, without user interaction the semantics of a closed door is applied to phone calls.

Pager:
                    A very simple receiver, a pager can only display short text messages, has a tiny display, and cannot send any messages.  Pagers can even be integrated into watches.  

Mobile Phones:
                    The traditional mobile phone only had a simple black and white text display and could send / receive voice or short messages.  Today, however, mobile phones migrate more and more toward PDAs.  Mobile phones with full color graphic display, on the internet browser are available.

Personal digital assistant:
                    PDAs typically accompany a user and officer very simple versions of office software (calendar, notepad, mail).  The typical input device is a pen, with built in character recognition translating hand writing into characters.  Web browsers and many other software packages are already available for these devices. 

Palmtop/pocket computer:
                    The next step toward full computer are pocket computers offering tiny keyboards, color displays, and simple versions of programs found on desktop computers (Text processing, Spread Sheets etc.,).

Notebook/Laptop:
                    Finally, laptops offer more or less the same performance as standard desktop computers; use the same software, the only technical difference being size, Weight, and ability to run on a battery.



A SIMPLIFIED REFERENCE MODEL
                                            The above diagram shows a personal digital assistant (PDA) which provides an example for a wireless and portable device.  This PDA communicates with a base station in the middle of the p9ictue.  The base station consists of a radio transceiver (sender and receiver) and an interworking unit connecting the wireless link with the fixed link.  Finally, on the right-hand side, the communication partner of the PDA, a conventional computer, is shown. 

                    Underneath each network element (such as PDA, interworking unit, computer), the figure shows the protocol stack implemented in the system according to the reference model.  End-systems, such as the PDA and computer in the example, need a full protocol stack co0mprising the application layer, transport layer, network layer, data link layer, and physical layer.  Applications on the end-systems communicate with each other using the lower layer services.  Intermediate systems, such as the interworking unit, do not necessarily need all of the layers. The figure shown only shows the network, data link, and physical layers. As (according to the basic reference model) only entities at the same level communicate with each other (i.e., transport with transport, network with network), the end-system applications do not notice the intermediate system directly in this scenario.  The following explain the functions, of each layer in more detail in a wireless and mobile environment.

  Physical Layer:
                    This lowest layer in a communication system is responsible for the conversion of a stream of bits into signals that can be transmitted on the sender side.  The physical layer of the receiver then transforms the signals back into a bit stream.  For wireless communication, the physical quency, signal detection (although heavy interference may disturb the signal), modulation of data onto a carrier frequency and (depending on the transmission scheme) encryption.

Data Link Layer:
                    The main tasks of this layer include accessing the medium, multiplexing of different data streams, correction of transmission errors, and synchronization (i.e., detection of a data frame). It is responsible for a reliable point-to-point connection between two devices or a point-to-multipoint connection between one sender and several receivers.

Network Layer:
                    This third layer is responsible for routing packets through a network or establishing a connection between two entities over many other intermediate systems.  Important topics are addressing, routing, device location, and handover between different networks. 

Transport Layer:
                    This layer is used in the reference model to establish an end-to-end connection.  Topics like quality of service, flow and congestion control are relevant, especially if the transport protocols known from the Internet, TCP and UDP, are to be used over a wireless link.

Application Layer:
                    Finally, the applications are situated on top of all transmission oriented layers.  Topics of interest in this context are service loation, support for multimedia applications, adaptive applications that can handle the large variations in transmission characteristics, and also wireless access to the World Wide Web using a portable device. 




Mobile world meets cyberspace

                   Mobile Internet is all about Internet access from mobile devices. Well, it’s true, but the ground realities are different. No doubt Internet has grown fast, well really fast! but mobile Internet is poised to grow even faster. The fundamental difference lies in the fact that whereas academics and scientists started the Internet, the force behind mobile Internet access is the cash-rich mobile phone industry. Mobile industry has always been looking for more avenues to make more money and in this attempt; the mobile industry besides carefully finding about the needs and requirements for a mobile data user is also creating new demand patterns also. What makes things even more favorable for the mobile Internet is that it already has a lot of Internet-based content from which to draw. This can be adapted for display on mobiles in a number of ways. A website can be viewed using a phone that is WAP-enabled.

                   A mobile is something that we take along with us where ever we go (unlike our computers) and that is one of the reasons many analysts believe that within three years more people will be accessing the Internet from mobile phones than from office or home computers.

                   Well, a variety of mobile wireless standards exist today, each have different levels of data capabilities. Thanks to the developments taking place in all the 2nd generation mobile wireless data technologies, and the high data speeds being promised by the 3rd generation systems, the distinction between the wireless, wireline and the Internet service providers is beginning to blur. Mobile Internet access surely is poised to be a major commercial success. While the underlying network technologies keep on evolving, what is going to differentiate on network from the other is finally the services that it provides to the end user. Data services provided by the mobile networks are fast becoming popular and in some countries in Europe people are spending more on mobile data access compared to voice services. This presents a huge opportunity for the mobile data service developers.

                   The issue is that with a range of mobile devices and underlying mobile wireless technologies, developing services specific to each type of equipment and specific to a particular technology is troublesome. An application written for specific equipment and a specific technology won’t work anywhere else. This calls for a standardization, which provides a generic model where applications can be written without keeping in mind the equipment and the technology. On the equipment side, the wireless devices represent the ultimate constrained computing device with:

·        Less powerful CPUs,
·        Less memory (ROM and RAM)
·        Restricted power consumption
·        Smaller displays
·        Different input devices (e.g., a phone keypad, voice input, etc.)
·        and on the network side, wireless networks are constrained by
·        Less bandwidth
·        More latency
·        Less connection stability
·        Less predictable availability

                   However, most important of all, wireless subscribers have a different set of essential desires and needs than desktop or even laptop Internet users.  With the emergence of 3G technologies, the constraint on the low data rates may not be as limiting as it is today but is must be understood clearly that, as bandwidth increases, the handset’s power consumption also increases which further taxes the already limited battery life of a mobile device. Therefore, even as wireless networks improve their ability to deliver higher bandwidth, the power availability at the handset will still limit the effective throughput of data to and from the device. A wireless data solution must be able to overcome these network limitations and still deliver a satisfactory user experience.

Here comes WAP!
                   The Wireless Application Protocol (WAP) is the de-facto world standard for the presentation and delivery of wireless information and telephony services on mobile phones and other wireless terminals. The WAP Forum has published a global wireless protocol specification, based on existing Internet standards such as XML and IP, for all wireless networks. The WAP specification is developed and supported by the wireless telecommunication community so that the entire industry and most importantly, its subscribers, can benefit from a single, open specification. WAP is designed to work with most wireless networks such as CDPD, CDMA, GSM, PDC, PHS, TDMA, FLEX, ReFLEX, iDEN, TETRA, DECT, DataTAC, Mobitex. Actually Phone.com, Ericsson, Nokia and many others began developing standards independently of each other, but it was soon realized that it would make more sense to focus development around a common standard. WAP forum was thus born with a desire to establish a common format for Internet transfers to mobile telephones, without having to customize the Internet pages for the particular display on every different mobile telephone or personal organizer.

                   The Wireless Application Protocol (WAP) addresses the issues mentioned above by introducing the concept of the Internet as a wireless service platform. By addressing the constraints of a wireless environment, and adapt existing Internet technology to meet these constraints, the WAP Forum has succeeded in developing a standard that scales across a wide range of wireless devices and networks. The WAP specifications complement existing wireless standards. For example, the WAP specification does not specify how data should be transmitted over the air interface. Instead, the WAP specification is intended to sit on top of existing bearer channel standards so that any bearer standard can be used with the WAP protocols to implement complete product solutions. It defines a protocol stack that can operate on high latency, low bandwidth networks such as Short Message Service (SMS), or GSM Unstructured Supplementary Service Data (USSD) channel. In addition to being air interface independent, the WAP specification is also independent of any particular device. Instead, it specifies the bare minimum functionality a device must have, and has been designed to accommodate any functionality above that minimum.

                   The WAP specification uses the best of existing standards, and has developed new extensions where needed. For example, a WAP Gateway communicates with other Internet nodes using the standard HTTP 1.1 protocol and the wireless handsets use the standard URL addressing scheme to request services. The WAP forum is also working with many other standards organizations to develop or modify standards related to new technologies, which need modifications for wireless environment. The WAP forum has liaison relationships (or is in the process of having) with Cellular Telecommunications Industry Association (CTIA), World Wide Web Consortium (W3C), Telecommunications Industry Association (TIA) and Internet Engineering Task Force (IETF). This ensures that when new standards emerge, these standards remain compatible with the work of the WAP Forum. For example, the WAP Forum will be working with the W3C and IETF to ensure future convergence with HTML-NG (Next Generation) and HTTP-NG specifications, and to provide input to these groups regarding the requirements of future wireless network technologies.

                   The Wireless Application Protocol is a standard developed by the WAP Forum, a group founded by Nokia, Ericsson, Phone.com (formerly Unwired Planet), and Motorola. The WAP Forum has now expanded to include more than 200 members, including operators, infrastructure suppliers, software developers and content providers.

Wireless Application Protocol – WAP


Where does WAP Fit in the Wireless Computing Application?

                   Three are three essential product components that you need to extend your host applications and data to WAP-enabled devices. These three components are:

1.     WAP Microbrowser – residing in the client handheld device
2.     WAP Gateway – typically on wireless ISP’s network infrastructure
3.     WAP Server - residing either on ISP’s infrastructure or on end user organization’s infrastructure

WAP Micro-browser
                   A WAP micro-browser is a client software designed to overcome challenges of mobile handheld devices that enables wireless access to services such as Internet information in combination with a suitable network server

                   Lots of WAP browsers and emulators are available free of cost which can be used to test your WAP pages. Many of these browsers and emulators are specific to mobile devices. For example the R380s WAP emulator is intended to be used for testing WML applications developed for the WAP Browser in the Ericsson Smart phone R380s. You can find a list of downloadable WML Browsers/ Emulators at

                    WAP emulators can be used to see how your site will look like on specific phones. As these images show, the same thing can look different on different mobile phones. So, the problems that web developer faces with the desktop browsers (Netscape/Iexplorer) is present here also. So, make sure you test your code on different mobile phones (or simulators)

WAP Products - Microbrowser, WAP Gateway, WAP servers WAP Gateway
                   The idea behind WAP specifications is to connect the mobile networks to the Internet.To connect these two mega-networks, the WAP Specification assumes there will be a WAP Gateway. At its simplest level, this is a stack converter, which will convert the WAP request into a Web request and the Web response into a WAP response. WAP Gateway is a piece of software that sits between the mobile device and the external network like the Internet. The gateway does the job of converting Internet content i.e. the WML pages into byte code (WMLC) which can be understood by a WAP device. Usually located on a server of a mobile operator it handles incoming requests from your WAP phone, takes care of the conversion required during WTLS/SSL sessions and handles incoming requests from your WAP phone. Although in theory, the gateway could also be made to convert the HTML page content itself on-the-fly as well, there are some problems. HTML pages can be full of graphics and with inline scripting. Converting these to WML may return something that is not of any relevance to anybody. Some of the WAP Gateway products that are now coming on to the market (such as Nokia's WAP Server) also provide hosting capabilities themselves. In future it could be possible to integrate your WAP Server into the mobile network to gain information about the subscriber's location.If you host your own gateways, then it may be required to maintain some sort of connection with the mobile network. For example, in case of GSM networks you may need to have say a dial up connection with the network's SMS engine or you may need to provide dial in modems for CSD access

(Circuit Switched Data, around 9.6 kbps data rate)
Source: WAP for web developers, anywhereyougo.com
                  
                   A WAP server is simply a combined web server and WAP gateway. WAP devices do not use SSL. Instead they use WTLS. Most existing web servers should be able to support WAP content as well. Some new MIME types need to be added to your web server to enable it support WAP content. MIME stands for Multipurpose Internet Mail Extension, and in the web context, MIME can be thought of as a piece of header information that comes down with every file sent from a web server to a browser.

Mobile Network Layer

                 This describes protocols and mechanisms developed for the network layer to support mobility.  The most prominent example is Mobile IP, which adds mobility support to the Internet network layer protocol IP.  While systems like GSM have been designed with mobility in mind from the very beginning, the Internet started at a time when no-one had a concept of mobile computers.  Therefore, the Internet of today lacks mechanisms for the support of users traveling through the world.  IP is the common base for thousands of applications and runs over dozens of different networks.  This is the reason for supporting mobility at the IP layer, mobile phone systems, for example, cannot offer this type of mobility for heterogeneous networks.

                    Another kind of mobility, rather portability of equipment, is supported by DHCP. In former times computers did not change their location often.  Today, due to laptops or notebooks, e.g., students show up at the university with their computers, want to plug them in or use wireless access.  A network administrator does not want to configure dozens of computers every day or hand out a list of valid IP addresses, DNS servers, subnet prefixes, default routers etc.  At this point the dynamic host configuration protocol (DHCP) sets in to support automatic configuration of computers.

Goals, assumptions, and requirements:

                    The Internet is the network for global data communication with hundreds of millions of users.  So why not simply use a mobile computer in the Internet?
                    The reason is quite simple: you will not receive a single packet as soon as you leave your home network, i.e., the network your computer is configured for, and reconnect your computer (wireless or wired) at another place.  The reason for this is quite simple if you consider routing mechanisms in the Internet.  A host sends an IP packet with the header containing a destination address besides other fields.  The destination address not only determines the receiver of the packet, but also the physical subnet of the receiver.  For example, the destination address 129.13.42.99 shows that the receiver must be connected to the physical subnet with the network prefix 129.13.42 (unless CIDR is used).  Routers in the Internet now look at the destination addresses of incoming packets and forward them according to internal look-up tables.  To avoid an explosion of routing tables, only prefixes are stored and further optimizations are applied.  Otherwise a router would have to store the addresses of all computers in the Internet, which is obviously not feasible.  As long as the receiver can be reached within its physical subnet, it gets the packets; as soon as it moves outside the subnet, no packet will reach it anymore.  Thus, a host needs a so called topologically correct address.




Quick ‘Solutions’:
                   
                   One might think of a quick solution to this problem by assigning the computer a new, topologically correct IP address.  So moving to a new location would also mean assigning a new address.  Now the problem is that nobody knows of this new address.  It is almost impossible to find a (mobile) host in the Internet which has just changed its address.  Especially the domain name system (DNS) need some time before it updates its internal tables necessary for the mapping of a logical name to an IP address.  This approach does not work if the mobile node moves quite often.  Furthermore, the Internet and DNS have not been built for frequent updates.  Just imagine millions of nodes moving at the same time.  DNS could never present a consistent view of names and address, for it uses caching to improve scalability.  It is simply too expensive to update quickly.
          Furthermore, there is a severe problem with higher layer protocols like TCP that rely on IP addresses. Changing the IP address while still having a TCP connection open means breaking the connection.  A TCP connection can be identified by the tuple (source IP address, source port, destination IP address, destination port), also known as a socket.  Therefore, a TCP connection cannot survive any address change.  Breaking TCP connections is not an option, using programs like telnet would be impossible.  Additionally, the mobile node would have to notify all communication partners about the new address.
         
                   Another approach is the creation of specific routes to the mobile node.  Routers always choose the best-fitting prefix for the routing decision.  If a router now has an entry for a prefix 129.13.42 and an address 129.13.42.99, it would choose the port associated with the latter for forwarding, if a packet with the destination address 129.13.42.99 comes in.  While it is theoretically possible to change all routing tables all over the world to create specific routes to a mobile node, this does not scale at all with the number of nodes in the Internet.  Routers are built for extremely fast forwarding, but not for fast updates of routing tables.  While the first is done with special hardware support, the latter is typically a piece of software which cannot handle the burden of frequent updates.  Furthermore, routers are the ‘brains’ of the Internet, holding the whole net together.  No service provider or system administrator would allow changes to the routing tables, probably sacrificing stability, just for the mobility of individual users.

Requirements:
         
                   Since the quick ‘solutions’ obviously did not work, a more general architecture had to be designed.  Many field trials and proprietary systems finally led to mobile IP as a standard to enable mobility in the Internet.  Several requirements accompanied the development of the standard:

·        Compatibility:    The installed base of Internet computers, i.e., computers running TCP/IP and connected to the Internet, is huge.  A new standard cannot require changes for applications or network protocols already in use.  People still want to use their favorite browser for WWW and do not change applications just for mobility.  The same holds for operating systems.  No-one would use another operating system only for mobility, so mobile IP has to be integrated into existing operating systems or at least work together with them.  Routers within the Internet should not necessarily require other software.  While it is possible to enhance the capabilities of some routers to support mobility, it is almost impossible to change all routers.  Furthermore, mobile IP has to remain compatible to all lower layers used for the standard non-mobile IP.  This means that mobile IP must not require special media or MAC/LLC protocols.  So mobile IP has to use the same interfaces and mechanisms to access the lower layers as IP does.  Finally, end-systems enhanced with a mobile IP implementation should still be able to communicate with fixed systems without mobile IP.  Mobile IP has to ensure that users can still access all the other servers and systems in the Internet.  But that also implies access all the other servers and systems in the Internet.  But that also implies using the same address format and routing mechanisms.

·        Transparency:  Mobility should remain ‘invisible’ for many higher layer protocols and applications.  Besides maybe noticing a lower bandwidth and some interruption in service, higher layers should continue to work even if the mobile computer changed its point of attachment to the network.  For TCP, for example, this means that the computer must keep its IP address as explained above.  If the interruption of the connectivity does not take too long, TCP connections survive the change of the attachment point.  Clearly, many of today’s applications have not been designed for use in mobile environments.  Therefore, the only effects of mobility should be a higher delay and lower bandwidth.  However, there are some applications for which it is better to be ‘mobility aware’.  Examples are cost-based routing or video compression.  Knowing that it is currently possible to use different networks, the software could choose the cheapest one.  Or if a video application knows that currently only a low bandwidth connection is available, it could use a different compression scheme.  Therefore, additional mechanisms are necessary to inform these applications about mobility.

·        Scalability and efficiency:   Introducing a new mechanism into the Internet must not jeopardize the efficiency of the network.  Enhancing IP for mobility must not generate many new messages flooding the whole network.  Furthermore, special care has to be taken considering the lower bandwidth of wireless links.  Many mobile systems will have a wireless link to an attachment point.  Therefore, only some additional packets should be necessary between a mobile system and a node in the network.  Looking at the number of computers connected to the Internet and at the growth rates of mobile communication, it is clear that a myriad device will participate in the Internet as mobile components.  Just think of cars, trucks, mobile phones, every seat in every plane around the world etc. – many of them will have some IP implementation inside and move between different networks, thus requiring mobile IP. Therefore, it is indispensable for a mobile IP to be scalable over a large number of participants in the whole Internet, worldwide.


·        Security: Mobility poses many security problems.  A minimum requirement is the authentication of all messages related to the management of Mobile IP.  It must be sure for the IP layer if it forwards a packet to a mobile host that this host really is the receiver of the packet.  The IP layer can only guarantee that the IP address of the receiver is correct.  There are no ways of preventing faked IP addresses or other attacks.  According to Internet philosophy this is left to higher layers.



CONCLUSION

                    Mobile Computing and Communications is useful for wireless Networks.  The study of different versions will give differences between Mobile Computing and Communications, Access Control, Security etc., the traditional mobile phone only had a simple black and white text display and could send / receive voice or short messages.  Today, however, mobile phones migrate more and more toward PDAs.  Mobile phones with full color graphic display, on the internet browser are available.

2 comments:

  1. This post is written in a very good and entails a lot of useful information for me. I am glad to find a good way of writing the post.

    Task management software

    ReplyDelete