Chapter 16 Distributed systems, concepts and design, 4th edition, 2005, Coulouris et al
Gabriella Hammarin
Ylva-Li
Lindh

• Mobile computing: How to handle connectedness of mobile devices
• Ubiquitous computing: Ubiquitous computing is the method of enhancing computer use by making many computers available throughout the physical environment, but making them effectively invisible to the user.
Mark Weiser the “father” of ubiquitous computing

• From the point of view of distributed systems, there is no essential difference between mobile and ubiquitous computing
• Volatility is not a definining property of m and u systems, other systems have that property as well. But mobile and ubiquitous computing is concerned about all kinds of volatility:
– failures of devices and communication links
– changes in the characteristics of communication such as bandwidht
– the creation and destruction of associations – logical communication relationships between software components resident on the devices

• Continuous connectivity
• Wireless communication without infrastructure
• Location awareness and resource discovery
• Security

Issues: How to stay connected when moving between networks or when external factors such as weather or environment interfere with signal reception, or nodes are removed
Possible solution: Solution exists to some of the problems but development is still in progress
– which way is the most efficient?

Issue: different networks use different infrastructures and standards to structure its inhabitant devices. As an outsider enters, it might be hard to find, recognize and interact with other devices in the network.
Possible solution: Standard protocols for association

Ubiquitous computing is the method of enhancing computer use by making many computers available throughout the physical environment, but making them effectively invisible to the user.
Mark Weiser, the “father” of ubiquitous computing

• Localized scalability. Communication over small and big distances.
• Invisibility/visibility. To find all relevant devices in a ”smart space” and only the relevant
• Resource constraints. E g size, battery limits, cost
• Ad hoc networks and topology control

Issue 1: to integrate devices in our environment to such degree that we no longer are aware of them
Issue 2: To find all relevant devices in a ”smart space” and only the relevant devices
Possible solution 2: The boundary principle: smart systems need to have system boundaries that correspond accurately to meaningful spaces as they are normally defined territorially and administratively.
Also, Discovery services, a directory service in which services in a smart space are registered and looked up by their attributes .

Ubiquitous computing: Localized scalability-
Communication over small and big distances
Issue: A greater distance between nodes leads to weaker communication because it’s more failure prone
Possible solution: Ad hoc networks which not includes an access point or base station. They are built ”on the fly” as a result of the mutual detection of two or more mobile devices with wireless interfaces on the same vicinity.

Issues: Both mobile and devices in a smart space need to be small (to be mobile and to be invisible) which makes battery time decrease. Also the range, cost and maintaining the connection is important. With and increased number of nodes, there will be a higher pressure on the network, causing negative effects on it’s bandwith.
Possible solution: …

1. How to reach nodes which are out of range – ad hoc networks, a combination of several smaller networks
2. Which devices should know about each other? Hierarchy, should all devices be aware of all other?

Issues:
- What basis of trust can there be between components that are able to associate spontaneously? (man in the middle)
- Privacy is a major issue for users who may distrust systems because of their sensing abilities.
- Users might not always be aware of being sensed. (Big brother problem/surveillance).

http://searchmobilecomputing.techtarget.com/searchMobileC omputing/downloads/Mobile_Computing_chp18.pdf

The End