Next Generation Wireless Applications: Creating Mobile Applications in a Web 2.0 and Mobile 2.0 World, 2nd Edition

10.5 NETWORK LAYER

Now, we come to consider the final layer in our layered abstraction of a mobile device that we have been discussing (refer to Figure 10.1) – the networking layer. This layer is concerned with getting data on and off of the device, so it is a key enabler of our mobile service world. Part of the network layer is the actual hardware to achieve wireless networking. We have already introduced some wireless networking technologies, particularly those that enable us to connect to the IP network layer in our mobile network model, namely digital cellular technologies and wireless LAN technologies. In Chapter 12, we shall describe in detail the RF network and explain its functions and characteristics.

In terms of the implementation of a wireless connection on a mobile device, we can think of the wireless hardware as a separate entity or module, usually referred to as a modem (stands for modulator/demodulator). An RF modem is a peripheral on the mobile device, just as the interfaces usually are (e.g. LCD display driver chip), and so we can generalise from the previous discussion about device drivers and software abstraction and apply the same principles to the task of interfacing to the modem. Typically, the modem will have a controller that facilitates the low-level software messaging interface with the microprocessor in our mobile device via the bus. This controller chip will have its own command set and protocols for receiving data via the bus to drive the functions ...