Mobile Networks
The power of a mobile application lies in its ability to communicate with other applications and so receive and transmit current information. For this a communication network is required. The king of networks is today the internet which in reality consists of a network of networks offering a standard set of mechanism’s for computers to identify each other and applications to exchange data. In the traditional world of desktop computers and servers the communication network is physically provided by cables between machines through which the network traffic flows. With mobile devices we lose the cables and we get in place a wireless network.
Voice and data services provided by the mobile network operators are provided though their cellular networks. Through a network of base stations, each of which serves a particular cell or region, nationwide coverage is built up. This offers the mobile subscriber access to the network with close to 100% coverage. Areas of intermittent or no coverage are termed black spots. These can include geographic areas where it is difficult to provide complete coverage such as valleys and tunnels, and the interior of some buildings in places such as basements etc.
This is an important point as a connection to the network may be required for certain applications and data services.
The cellular mobile networks provided by the public mobile operators were originally developed for voice communications only. Before the development of public cellular networks a number proprietary networks existed for use by certain communities for the delivery of voice or data services to mobile users. Following the massive adoption of the cellular networks many of the earlier proprietary networks have been discontinued with their service transferred to the public mobile operators. Some still remain however such as those used by the emergency services where a dedicated network is required.
All European mobile networks are built to a specification termed GSM. This means that a user in one European country can use their mobile phone in another. GSM was designed as a network for carrying voice traffic in what is know as circuit switched mode. (CSD). This can simply be though of as one user talking to another over a dedicated circuit setup for that conversation. The main point to make about CSD is that the user is billed based on the time spent on the call.
When GSM was being designed a small data service was built into the specification. This was termed the ‘short message service’ which is now know as SMS and which has grown beyond all initial expectations. Applications using this service are described in SMS section.
Alongside the growth of networks in the desktop computing environment came the increasing use of dialup connections for computers to connect to other computers via a standard fixed telephone line using a circuit switched connection. This was accomplished through the use of a device know as a modem which performed the physical link between computer and phone network. Eventually the same concept was carried over to the GSM Mobile phone networks with modems being built into the phones. This meant a mobile phone could be plugged into a computer via a cable and the computer could then dialup and connect to other computers via the mobile network. Public use of mobile computing was underway and this approach is still widely used today.
There are some drawbacks to connecting through a GSM modem however. The biggest problem is the cost. Because the connection is through CSD the user pays for the time of the connection. The mobile networks could not transmit data as fast as fixed line networks and so typically connection times would be long and costs high.
To fix this problem the GSM network was extended with a feature known as GPRS (General Packet Radio Switch). This allowed data to be transmitted across the mobile network in packets rather than through a CSD connection. This had two main benefits. The data transmission rates were faster than previously and, more importantly, the user was only billed for the amount of data sent and received on the mobile network. GPRS offered the first truly usable public data network for use by mobile computing devices. It also allowed mobile computing devices of many shapes and sizes to become part of the massive Internet phenomenon. Internet connected applications from mobile devices had become a reality!
Bookmark at del.ico.us
Bookmark at Digg