3.4 Connection Types
As discussed in Chapter 1, mobile devices typically operate in one of three modes: always connected, partially connected, and never connected (see Figure 3-15). These modes are described in more detail in the sections that follow.
Figure 3-15 Connection types
3.4.1 Always Connected
A mobile device, such as a cellular telephone or RIM device, normally operates in an always connected mode. In fact, RIM coined the phrase "always on, always connected."
An enterprise might have a wireless network and set of applications and servers that allow employees to connect and use their mobile devices while on company premises. Mobile devices, such as PDAs, Tablet PCs, and Laptop PCs, then essentially become extensions of the existing applications and infrastructure, permitting users the ability to always be connected to the applications while freely moving about the office.
3.4.2 Partially Connected
While the vision has been that mobile devices should always be connected, there are many scenarios where the mobile device is actually out of contact for extended periods of time.
Ironically, to a mobile application developer, this is where things are most interesting. For example, a mobile office worker might periodically connect to a server at the office to obtain email, contact information, or tasks to be done. The worker then disconnects the mobile device and carries out his/her normal tasks away from the office, during which time he/she might refer to the downloaded information. The user might also update the information locally on his/her mobile device before reconnecting at a later time to resynchronize the mobile device with the server.
3.4.3 Never Connected
There are also several mobile devices that never connect to back-end systems, such as certain gaming devices. While we have included this section for completeness, we will not be discussing these devices in this book.