3G:3G, short for third Generation, is the3rd generation of mobile telecommunications technology. Also called Tri-Band 3G.

3G telecommunication networks support services that provide an information transfer rate of at least 200Kbit/s. However, many services advertised as 3G provide higher speed than the minimum technical requirements for a 3G service. Recent 3G releases, often denoted 3.5G and 3.75G, also provide mobile broadband access of several Mbit/s  to smartphones and mobile modems in laptop computers.
3G finds application in wireless voice telephony, mobile internet access,fixed wireless Internet access, video calls and mobile TV..

This is a set of standards used for mobile devices and mobile telecommunication services and networks that comply with theInternational Mobile Telecommunications-2000 (IMT-2000) specifications by the International Telecommunication Union. 3G finds application in wireless voice telephony, mobile Internet access, fixed wireless Internet access, video calls and mobile TV.

The above systems and radio interfaces are based on spread spectrum radio transmission technology. While the EDGE standard ("2.9G"), DECT cordless phones and Mobile WiMAX standards formally also fulfill the IMT-2000 requirements and are approved as 3G standards by ITU, these are typically not branded 3G, and are based on completely different technologies.
A new generation of cellular standards has appeared approximately every tenth year since 1G systems were introduced in 1981/1982. Each generation is characterized by new frequency bands, higher data rates and non backwards compatible transmission technology. The first release of the 3GPP Long Term Evolution (LTE) standard does not completely fulfill the ITU 4G requirements called IMT-Advanced. First release LTE is not backwards compatible with 3G, but is a pre-4G or 3.9G technology, however sometimes branded 4G by the service providers. Its evolution LTE Advanced is a 4G technology. WiMAX is another technology verging on or marketed as 4G.

Detailed breakdown of 3G systems

The 3G research and development projects started in 1992. In 1999, ITU approved five radio interfaces for IMT-2000 as a part of the ITU-R M.1457 Recommendation; WiMAX was added in 2007.
There are evolutionary standards (EDGE and CDMA) that are backwards-compatible extensions to pre-existing 2G networks as well as revolutionary standards that require all-new network hardware and frequency allocations. The cell phones used utilize UMTS in combination with 2G GSM standards and bandwidths, but do not support EDGE. The latter group is the UMTS family, which consists of standards developed for IMT-2000, as well as the independently developed standardsDECT and WiMAX, which were included because they fit the IMT-2000 definition.

Data rates
ITU has not provided a clear definition of the data rate users can expect from 3G equipment or providers. Thus users sold 3G service may not be able to point to a standard and say that the rates it specifies are not being met. While stating in commentary that "it is expected that IMT-2000 will provide higher transmission rates: a minimum data rate of 2 Mbit/s for stationary or walking users, and 384 kbit/s in a moving vehicle,"the ITU does not actually clearly specify minimum or average rates or what modes of the interfaces qualify as 3G, so various rates are sold as 3G intended to meet customers' expectations of broadband data.
Security
3G networks offer greater security than their 2G predecessors. By allowing the UE (User Equipment) to authenticate the network it is attaching to, the user can be sure the network is the intended one and not an impersonator. 3G networks use theKASUMI block cipher instead of the older A5/1 streamcipher. However, a number of serious weaknesses in the KASUMI cipher have been identified.
In addition to the 3G network infrastructure security, end-to-end security is offered when application frameworks such as IMS are accessed, although this is not strictly a 3G property.
Applications of 3G
The bandwidth and location information available to 3G devices gives rise to applications not previously available to mobile phone users. Some of the applications are:

• Mobile TV
• Video on demand
• Video conferencing
• Telemedicine
• Location based services
• Global Positioning System(GPS).

Reference:

Wireless communication
By:
 Andrea Goldsmith
 Stanford University MCSE TRAINING GUIDE
 TCP/IP
By:
  Emmett Dulaney
 John white
 Sherwood Lawrence
 Raymondwilliams
 Robert Scrimger
 kevinwolford
 Anthony tilke
 http://en.wikipedia.org/wiki/3G

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