What is 2G?
2G (or 2-G) is short for second-generation wireless telephone technology. The main differentiator to previous mobile telephones, retroactively dubbed 1G, is that 1G networks process analog data but 2G networks are digital. This allowed a considerable improvement in voice quality, as digital information is not subject to distortions in the same way as analog information, and also increased capacity as calls can be multiplexed more efficiently. 2G networks may offer an optional service to transfer low-speed data, such as email or software, in addition to the digital voice call itself. SMS messaging is also available as a form of data transmission for some standards.
2G services are frequently referred as Personal Communications Service or PCS in the US.
2G technologies can be divided into TDMA-based and CDMA-based standards depending on the type of multiplexing used. The main 2G standards are: GSM (TDMA-based), IDEN (TDMA-based), IS-136 aka D-AMPS, (TDMA-based, IS-95 aka cdmaOne, (CDMA-based).
2.5G is a stepping stone between 2G and 3G cellular wireless technologies. The term “second and a half generation” is used to describe 2G-systems that have implemented a packet switched domain in addition to the circuit switched domain. It does not necessarily provide faster services because bundling of timeslots is used for circuit switched data services (HSCSD) as well.
While the terms “2G” and “3G” are officially defined, “2.5G” is not. It was invented for marketing purposes only. 2.5G provides some of the benefits of 3G (e.g. it is packet-switched) and can use some of the existing 2G infrastructure in GSM and CDMA networks. GPRS is a 2.5G technology used by GSM operators.
Source: Wikipedia
