Mobile and ubiquitous computing




Technological advances in device miniaturization and wireless networking have led increasingly to the integration of small and portable computing devices into distributed systems.

These devices include:

  • Laptop computers.
  • Handheld devices, including mobile phones, smart phones, GPS-enabled devices, pagers, personal digital assistants (PDAs), video cameras and digital cameras.
  • Wearable devices, such as smart watches with functionality similar to a PDA.
  • Devices embedded in appliances such as washing machines, hi-fi systems, cars and refrigerators.

The portability of many of these devices, together with their ability to connect conveniently to networks in different places, makes mobile computing possible. Mobile computing is the performance of computing tasks while the user is on the move, or visiting places other than their usual environment. In mobile computing, users who are away from their ‘home’ intranet (the intranet at work, or their residence) are still provided with access to resources via the devices they carry with them. They can continue to access the Internet; they can continue to access resources in their home intranet; and there is increasing provision for users to utilize resources such as printers or even sales points that are conveniently nearby as they move around. The latter is also known as location-aware or context-aware computing.

Mobility introduces a number of challenges for distributed systems, including the need to deal with variable connectivity and indeed disconnection, and the need to maintain operation in the face of device mobility.
Ubiquitous computing is the harnessing of many small, cheap computational devices that are present in users’ physical environments, including the home, office and even natural settings. The term ‘ubiquitous’ is intended to suggest that small computing devices will eventually become so pervasive in everyday objects that they are scarcely noticed. That is, their computational behaviour will be transparently and intimately tied up with their physical function.

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Mobile and ubiquitous computing

The presence of computers everywhere only becomes useful when they can communicate with one another. For example, it may be convenient for users to control their washing machine or their entertainment system from their phone or a ‘universal remote control’ device in the home. Equally, the washing machine could notify the user via a smart badge or phone when the washing is done. Ubiquitous and mobile computing overlap, since the mobile user can in principle benefit from computers that are everywhere. But they are distinct, in general. Ubiquitous computing could benefit users while they remain in a single environment such as the home or a hospital. Similarly, mobile computing has advantages even if it involves only conventional, discrete computers and devices such as laptops and printers. Figure 1.4 shows a user who is visiting a host organization. The figure shows the user’s home intranet and the host intranet at the site that the user is visiting. Both intranets are connected to the rest of the Internet.

The user has access to three forms of wireless connection. Their laptop has a means of connecting to the host’s wireless LAN. This network provides coverage of a few hundred metres (a floor of a building, say). It connects to the rest of the host intranet via a gateway or access point. The user also has a mobile (cellular) telephone, which is connected to the Internet. The phone gives access to the Web and other Internet services, constrained only by what can be presented on its small display, and may also provide location information via built-in GPS functionality. Finally, the user carries a digital camera, which can communicate over a personal area wireless network (with range up to about 10m) with a device such as a printer.

With a suitable system infrastructure, the user can perform some simple tasks in the host site using the devices they carry. While journeying to the host site, the user can fetch the latest stock prices from a web server using the mobile phone and can also use the built-in GPS and route finding software to get directions to the site location. During the meeting with their hosts, the user can show them a recent photograph by sending it from the digital camera directly to a suitably enabled (local) printer or projector in the meeting room (discovered using a location service). This requires only the wireless link between the camera and printer or projector. And they can in principle send a document from their laptop to the same printer, utilizing the wireless LAN and wired Ethernet links to the printer.

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This scenario demonstrates the need to support spontaneous interoperation, whereby associations between devices are routinely created and destroyed – for example by locating and using the host’s devices, such as printers. The main challenge applying to such situations is to make interoperation fast and convenient (that is, spontaneous) even though the user is in an environment they may never have visited before. That means enabling the visitor’s device to communicate on the host network, and associating the device with suitable local services – a process called service discovery.



Frequently Asked Questions

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Ans: The Internet is also a very large distributed system. It enables users, wherever they are, to make use of services such as the World Wide Web, email and file transfer. (Indeed, the Web is sometimes incorrectly equated with the Internet.) view more..
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Ans: the emergence of ubiquitous computing coupled with the desire to support user mobility in distributed systems view more..
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Ans: a very different style of underlying architecture from the styles mentioned above (for example client-server), and such systems typically employ what is known as distributed event-based systems. view more..
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Ans: Technological advances in device miniaturization and wireless networking have led increasingly to the integration of small and portable computing devices into distributed systems. view more..
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Ans: The crucial characteristic of continuous media types is that they include a temporal dimension, and indeed, the integrity of the media type is fundamentally dependent on preserving real-time relationships between elements of a media type. view more..
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Ans: hysical resources such as storage and processing can be made available to networked computers, removing the need to own such resources on their own. At one end of the spectrum, a user may opt for a remote storage facility for file storage requirements view more..
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Ans: In practice, patterns of resource sharing vary widely in their scope and in how closely users work together. At one extreme, a search engine on the Web provides a facility to users throughout the world, users who need never come into contact with one another directly. At the other extreme, in computer-supported cooperative working (CSCW), a group of users who cooperate directly share resources such as documents in a small, closed group. view more..
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Ans: Data types such as integers may be represented in different ways on different sorts of hardware – for example, there are two alternatives for the byte ordering of integers. These differences in representation must be dealt with if messages are to be exchanged between programs running on different hardware view more..
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Ans: the publication of interfaces is only the starting point for adding and extending services in a distributed system. The challenge to designers is to tackle the complexity of distributed systems consisting of many components engineered by different people. view more..
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Ans: a firewall can be used to form a barrier around an intranet, restricting the traffic that can enter and leave, this does not deal with ensuring the appropriate use of resources by users within an intranet, or with the appropriate use of resources in the Internet, that are not protected by firewalls. view more..
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Ans: ly and efficiently at many different scales, ranging from a small intranet to the Internet. A system is described as scalable if it will remain effective when there is a significant increase in the number of resources and the number of users. The number of computers and servers in the Internet has increased dramatically. view more..
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Ans: Failures in a distributed system are partial – that is, some components fail while others continue to function. Therefore the handling of failures is particularly difficult. The following techniques for dealing with failures are discussed throughout the book view more..
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Ans: he process that manages a shared resource could take one client request at a time. But that approach limits throughput. Therefore services and applications generally allow multiple client requests to be processed concurrently. view more..
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Ans: oncealment from the user and the application programmer of the separation of components in a distributed system, so that the system is perceived as a whole rather than as a collection of independent components view more..
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Ans: Reliability and security issues are critical in the design of most computer systems. The performance aspect of quality of service was originally defined in terms of responsiveness and computational throughput, but it has been redefined in terms of ability to meet timeliness guarantees, as discussed in the following paragraphs view more..
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Ans: The Web began life at the European centre for nuclear research (CERN), Switzerland, in 1989 as a vehicle for exchanging documents between a community of physicists connected by the Internet [Berners-Lee 1999]. A key feature of the Web is that it provides a hypertext structure among the documents that it stores, reflecting the users’ requirement to organize their knowledge. view more..
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Ans: Resource sharing is the main motivating factor for constructing distributed systems. Resources such as printers, files, web pages or database records are managed by servers of the appropriate type. For example, web servers manage web pages and other web resources. Resources are accessed by clients – for example, the clients of web servers are generally called browsers. view more..
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Ans: Physical models consider the types of computers and devices that constitute a system and their interconnectivity, without details of specific technologies. view more..



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