This month's jargon buster looks back at the evolution of mobile phone technology and forward to the world of 3G.

The first generation of mobile phones provided voice communications. They are known as analogue systems because they used analogue modulation. Modulation is the method by which information (ie voice) is carried by the radio signal. The system used in the UK was TACS (Total Access Cellular System).

The second generation (2G) of mobile phones in the UK used the Global System for Mobile Communications (GSM) standard, which is a digital system (it uses digital modulation to place the speech and data onto the radio channel). Short Messaging Services (SMS), which enables mobile phone users to send text messages of up to 160 charcers to other GSM mbile phone users, is part of the GSM standard.

Standard GSM communications are circuit switched, which means that a physical path is obtained for and dedicated to a single connection between two end-points in the network for the duration of the connection. Circuit switched communications are suitable for voice calls, where there is continuous transfer of information at a fairly constant data rate.

Data commuinications, where short bursts at a high data rate are interspersed with periods of no communication, need a different type of connection: packet switched communications send data in units or packets that can be sent to their destination by different routes and mixed up with packets from otehr users' communciations.

Where the move from first to second generation mobile systems was a revolution, the move from 2G to third generations (3G) will be an evolution. 3G aims to provide users with broadband packet-based transmission of text, digitized voice, video and multimedia at data rates up to 2Mbps (megabits per second). 3G networks will be based on evolved GSM networks, and in the meantime 2G standards continue to develop, with new services and capabilities being introduced.

2.5G (generation 2.5) refers to these enhanced 2G networks which will introduce users to basic 3G type services, including:

WAP (wireless application protocol), a communication protocol which standardizes the way that wireless devices, particularly cellular telephones, can be used for Internet access, including e-mail (see Oftel News 49). i-mode, the packet-based service for mobile phones offered by NTT DoCoMo in Japan, uses a simplified version of Hypertext Markup Language (HTML) called Compact Wireless Markup Language (CWML), whereas WAP uses Wireless Markup Language (WML). The i-mode wireless data service offers colour and video over many phones. Its mobil computing service enables users to send and receive e-mail, access the Internet, conduct stock transactions and make airline reservations.

HCSD (high-speed circuit switched data), circuit-switched wireless data transmission which will increase data rates for GSM users up to 38.4 kbps, comparable to the speed of current domestic modems and four times faster than the standard GSM data rate.

GPRS (General Packet Radio Service), a packet-based wireless communication service that promises data rates on GSM networks from 56 up to 114 kbps and continupus connection to the Internet. The higher data rates will allow users to take part in video conferences and interact with multimedia websites and similar applications using mobile handheld devices, eg phones, PDAs (personal digital assistants) and notebook computers.

EDGE (Enhanced Data GSM Environment) is designed to deliver data on GSM networks at rates up to 384 kbps and enable the delivery of multimedia and other broadband applications to mobile phone and computer users.

The standard being finalised for 3G systems in Europe is based on GSM. It is being developed by the Third Generation Partnership Project (3GPP), a group of regional standards bodies from Europe (European Telecommunication Standards Institute ETSI)), Japan, China, Korea and the United States.

This standard will be one of the international family of 3G standards, known as IMT2000 (International Mobile Telecommunications 2000), brought together in the Internaional Telecommunications Union (ITU).