Unit 12 Mobile systems Flashcards
What are the two types of portability?
(Part 2) The two types of portability:
- Physical portability is the ability ot move the computational device easily from one location to another
- Application portability is the ability to easily adapt an application in order to make it run on various platforms
Even if the system is not mobile, why are wireless sensor networks usually ad-hoc?
(Part 2) Being ad-hoc allows the network to automatically accomodate the addition and removal of sensors. Moreover, ad-hoc networks are more robust to node failure, which in this case means that routing can dynamically bypass any sensors that are not working.
Give an example of mobile code from a previous unit?
(Part 3) A typical example of mobile code is an applet (Unit 9 Subsection 3.1), which is transferred from the server to the client’s machine and executed there.
Does the JVM implement strong mobility?
(Part 3) JVM has the required common memory areas for storing all code and all the objects (the heap), and a per-thread area to store the program counter, registers and activation stack. However, the only mechanisms to transfer information across JVMs are object serialisation and class loading. Threads (execution units) can hence not be transferred from one JVM to another, which means that only weak mobility is supported.
In what way do mobile systems reinforce he fallacy that, the network is reliable?
(Part 5) Mobile systems often use wireless communication, which is less reliable than wired communication. For example, a simple movement of a device may interrupt its line-of-sight intfra-red communication with another device. Or radio signals can be cut off by going underground.
