Mobile Computing

Our Mobile System Architecture supports applications by a middleware stub. Based on these architecture prototypes for Mobile Database Access (MODBC), Mobile Information Access (MWWW) and Mobile File Access (MLDAP) have been built to demonstrate the usability of the proposed approach. The research addresses topics like Application Stability in mobile environments, Multimedia, Quality of Service, Bandwidth and cost awareness, application transparency and Security.Introduction: Mobile Computing is agenericterm describing your ability to use technology 'untethered', that is not physically connected, or in remote or mobile (non static) environments. The term is evolved in modern usage such that it requires that the mobile computing activity be connected wirelessly to and through the internet or to and through a private network. This connection ties the mobile device to centrally s through the use of battery powered, portable, and wireless computing and communication devices.This includes devices like laptops with wireless LAN or wireless WAN technology, smart mobile phones, wearable computers and Personal Digital Assistants (PDAs) with Bluetooth or IRDA interfaces.

Many types of mobile computers have been introduced since the 1990s, including the:

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• Laptop computer
• Subnotebook
• Personal digital assistant (PDA)
• Portable data terminal (PDT)
• Mobile data terminal (MDT)
• Tablet personal computer
• Smart phone
• UMPC What is mobile computer?
• A computer which you can take with you all around. You can do all the things which can be done with a desktop computer.
• You should be able to use same software, which you use on a desktop computer. Mobile computer - How?
• One possibility is to have a standalone computer capable of storing large amount of software and data files, processing power to support the required applications.
• Modern day laptop computer are something like this.
• Whenever you are static, connect to internet through an access point and you can do the file transfer, telnet, web browsing etc. While on the move, connectivity is desired for using software which requires cooperation of at least two machines.

History of mobile devices:

Originally, electronic devices such as radio transmitters, wireless communications systems, and the like, were base stations, operated at fixed locations, typically with large antenna towers. Widespread use of automobiles gave rise to smaller devices operating at 6 volts. In the 1950s, the transition to 12 volt automotive electrical systems gave rise to a large number of 12 volt devices, such as two-way radios, referred to as mobile rigs.A large industry, with companies such as Motorola sprung up to support the growing need for mobile devices, such as taxicab radios, police radios, and other 12 volt under dash equipment, as well as trunk mount systems. Today there are a wide variety of mobile computing platforms, including dash-mount VGA displays, and computers that can provide GPS and other navigation functions for automobile users.

Architecture:

Addressing the above mentioned tasks we propose a mobility supporting architecture.This architecture consists of a Mobility Service Architecture, describing the way we implement our mobility services in a computer system, and a Mobility Environment Architecture describing how data are transmitted between computers in mobile environments and what tasks the different stations fulfill in our architecture Mobility Services Architecture: Mobility services can be classified into three groups.

First there are services designed to overcome common restrictions of mobile computing, which arise mainly from the slowness, insecurity and instability of wireless or analogous connection lines utilized by the mobile user.These services are called common mobility services (CMS). Examples are connection management, caching or encryption services. The second group of services handles the management and administration of mobile users moving around and connecting their portables to networks at different places. These mobility management services (MMS) include tasks such as the authentication of users, accounting and billing issues or profiling of the users' habits.The tasks necessary to adapt certain existing applications to mobile usage are implemented by high level services, which are called special mobility services (SMS). Special mobility services adapt existing services to the mobile conditions.

For example to allow remote database access over a wireless connection line one has to take special care of possible frequent connection losses especially in the context of the state of the database. Viewing services as distinct building blocks, we are able to sketch an architecture for a "mobility services enhanced system".

Mobility environment architecture:

To overcome restrictions in mobile computing the above architecture was designed; the architecture consists of the following parts: The network environment consists of mobile hosts fixed hosts and certain access points. The fixed hosts are all connected to a backbone (i. e. the Internet). Mobile hosts usually don't contact them directly, but use physically closer located hosts as access points to the backbone for means of minimizing the distance which has to be bridged by a mobile connection line.

In addition to the users carrying a portable computer with them, also mobile users travelling between fixed hosts are considered in our system. MWWW: Using HTTP with wireless communication over slow and expensive lines produces long times of opened connection, unnecessary connection establishments and therefore high costs. Mobile-WWW introduces an extension for HTTP which uses an intelligent compression and administration mechanism to save connection time and money.Mobile-WWW consists of a special Web-client which requests a quality of service for the content; this QoS is defined according to the users preferences, the available bandwidth and the cost of transmission. The server compresses the data in accordance to the values of the quality of service. Because the server knows the type of the data that has to be compressed the optimal compression factor and method could be chosen. For text and hyper text compression we are using a Huffman code with dictionaries installed on every participating system.

For graphic, video and sound we are using standard compression tools with lossless or lossy compression according to the values of the requested quality of service.

MLDAP:

Ever since, because of its versatility the file system has been the favorite data storage for computer system users. Therefore optimizing file access from mobile systems is most important for certain applications. The MLDAP - Mobile file access using LDAP - system provides file access from mobile devices without bothering applications or users with the specific effects of their mobility. A consistent view of all files is generated even if the files are spread over different locations in heterogeneous environments. Files could be stored on both mobile and stationary systems, using different operating systems and eventually even replicating files within the global file system. The consistent view on this situation is achieved by exploiting the special properties of mobile systems and by falling back upon existing knowledge about distributed file systems such as Coda and Focus.

Mobile devices - namely PDAs like Apple Newton, Psion and Windows systems - are mainly characterized by their small size and their usually weak computing power if compared to stationary computer systems. These restrictions (among others, e. g. weak displays etc. ) lead to a number of classes of applications, which are especially well suited for being used with PDAs. Among the typical applications used with PDAs in every-day scenarios are "Notepad", "Address Book", "Calendar", "Communication" (by email), and "Information Retrieval" (by the means of the WWW).These applications can be found on almost every PDA by default.

The data are stored in files with well known file semantic, which is vital for the implementation of Rich File Access and automatic conflict resolution as used by MLDAP. MLDAP is open and useful to any class of application, which is achieved mostly by the consistent view of the file system without regard to the actual location of the different files. When working with mobile applications, users typically do not need all data but merely the part of it, which is relevant to the tasks performed by the user.For example, imagine the application "Calendar". Usually, not the whole calendar but only the actual and future appointments are required by the user. The data of the typical applications mentioned above can easily be split into logical parts, e. g. one day out of a one-year calendarium. Furthermore; it is quite easy to generate a summary of the data (e. g. the table of content of a lengthy text).

Challenges of Mobile Computing:

Mobility:

• Address Migration
• Current wired networks - not designed for dynamically Changing addresses. Each host name is bound to a network address (in TCP/IP world DNS server does this binding)
• Moving to new location means acquiring new network address the binding need to be modified.
• The binding info cannot be cached with long expiration time in the network.
• The address of mobile host is changing much faster due to mobility.
• To communicate with mobile host - message should be sent to its most recent address.
• For all active connections, mobile host should keep on informing about change in address to all the hosts at other ends.

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