2G

2G (or 2-G) is short for second-generation wireless telephone technology. Second-generation 2G cellular telecom networks were commercially launched on the GSM standard in Finland by Radiolinja (now part of Elisa Oyj) in 1991. Three primary benefits of 2G networks over their predecessors were that phone conversations were digitally encrypted; 2G systems were significantly more efficient on the spectrum allowing for far greater mobile phone penetration levels; and 2G introduced data services for mobile, starting with SMS text messages. 2G technologies enabled the various mobile phone networks to provide the services such as text messages, picture messages, and MMS (multimedia messages). All text messages sent over 2G are digitally encrypted, allowing for the transfer of data in such a way that only the intended receiver can receive and read it.

After 2G was launched, the previous mobile telephone systems were retroactively dubbed 1G. While radio signals on 1G networks are analog, radio signals on 2G networks are digital. Both systems use digital signaling to connect the radio towers (which listen to the handsets) to the rest of the telephone system.

2G has been superseded by newer technologies such as 2.5G, 2.75G, 3G, and 4G; however, 2G networks is already obsolete.

2G Technologies
2G technologies can be divided into time division multiple access (TDMA)-based and code division multiple access (CDMA)-based standards depending on the type of multiplexing used. The main 2G standards are:
 * GSM (TDMA-based), originally from Europe but used in most of the world outside North America. Today accounts for over 80% of all subscribers around the world. Over 60 GSM operators are also using CDMA2000 in the 450 MHz frequency band (CDMA450).
 * IS-95 a.k.a. cdmaOne (CDMA-based, commonly referred as simply CDMA in the US), used in the Americas and parts of Asia, accounts for about 17% of all subscribers globally. Over a dozen CDMA operators have migrated to GSM including operators in Mexico, India, and Australia.
 * PDC also known as JDC (Japanese Digital Cellular) (TDMA-based), used exclusively in Japan
 * iDEN (TDMA-based), proprietary network used by Nextel in the United States and Telus Mobility in Canada
 * IS-136 a.k.a. Digital AMPS or D-AMPS (TDMA-based, commonly referred as simply 'TDMA' in the US), was once prevalent in the Americas, but most have migrated to GSM.

2G services are frequently referred as Personal Communications Service, or PCS, in the United States.

Capacity
Using digital signals between the handsets and the towers increases system capacity in two key ways:
 * Digital voice data can be compressed and multiplexed much more effectively than analog voice encodings through the use of various codecs, allowing more calls to be transmitted in same amount of radio bandwidth.
 * The digital systems were designed to emit less radio power from the handsets. This meant that cells had to be smaller, so more cells had to be placed in the same amount of space. This was possible because cell towers and related equipment had become less expensive.

2G Data Transmission Capacity:
 * With General Packet Radio Service (GPRS), there is a theoretical maximum transfer speed of 50 kbit/s (40 kbit/s in practice).
 * With EDGE (Enhanced Data Rates for GSM Evolution), there is a theoretical transfer speed of max. 1 Mbit/s (500 kbit/s in practice).

Disadvantages

 * In less populous areas, the weaker digital signal transmitted by a cellular phone may not be sufficient to reach a cell tower. This tends to be a particular problem on 2G systems deployed on higher frequencies, but is mostly not a problem on 2G systems deployed on lower frequencies. National regulations differ greatly among countries which dictate where 2G can be deployed.
 * As distance increases, analog reception degrades gradually, but digital reception abruptly transitions from clear reception to no reception. This can be both an advantage and a disadvantage. Under good conditions, digital will sound better. Under slightly worse conditions, analog will experience static, while digital has occasional dropouts. As conditions worsen, though, digital will start to completely fail, by dropping calls or being unintelligible, while analog slowly gets worse, generally holding a call longer and allowing at least some of the audio transmitted to be understood.

Advantage

 * Digital calls tend to be free of static and background noise, although the lossy compression used reduces audio quality, meaning that the range of call sound is reduced. Talking on a digital cell phone, a caller hears less of the tonality of someone's voice.

Evolution
2G networks were built mainly for voice services and slow data transmission (defined in IMT-2000 specification documents), but are considered by the general public to be 2.5G or 2.75G services because they are several times slower than present-day 3G service.

2.5G (GPRS)
2.5G ("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 service because bundling of timeslots is used for circuit-switched data services (HSCSD) as well.

The first major step in the evolution of GSM networks to 3G occurred with the introduction of General Packet Radio Service (GPRS). CDMA2000 networks similarly evolved through the introduction of 2.5G. Its approach centred on the use of packet data. Up until this time all circuits had been dedicated to a given user in an approach known as circuit switched, i.e. where a complete circuit is switched for a given user. This was inefficient when a channel was only carrying data for a small percentage of the time. The new packet switched approach routed individual packets of data from the transmitter to the receiver allowing the same circuit to be used by different users. This enabled circuits to be used more efficiently and charges to be metered according to the data transferred.

2.75G (EDGE)
GPRS networks evolved to EDGE networks with the introduction of 8PSK encoding, While the symbol rate remained the same at 270.833 samples per second, each symbol carried three bits instead of one. Enhanced Data rates for GSM Evolution (EDGE), Enhanced GPRS (EGPRS), or IMT Single Carrier (IMT-SC) is a backward-compatible digital mobile phone technology that allows improved data transmission rates, as an extension on top of standard GSM. EDGE was deployed on GSM networks beginning in 2003—initially by AT&T in the United States.

EDGE is standardized by 3GPP as part of the GSM family and it is an upgrade that provides a potential three-fold increase in capacity of GSM/GPRS networks.The 2G digital service provided very useful features, such as caller ID, call forwarding, and short messaging.

Australia
Telstra announced that they will shut down their GSM network by the end of 2016.

Optus announced that they will shut down their GSM network in April 2017.

Canada
Rogers Wireless is the only provider still having a 2G network, until 2018.

Singapore
The NEA which is the national authority for radiation protection in Singapore, only requires to comply with the World Health Organisation recommendation, compared to bigger markets, where the statutory requirements have 10 times stricter exposure limits even with more topography challenges.

All 2G services are shut down by 2015, and by now nobody is using 2G networks as of now. All of them are using 3G or 4G networks, which is better and more efficient for elderly, adults and young children, as we have passed many generations.

United States
Various carriers such as AT&T have made announcements that 2G GSM technology in the United States is in the process of being shut down so that carriers can reclaim those radio bands and re-purpose them for future technology needs. The shutdown will be complete by the end of 2016. All users of AT&T's 2G GSM service will lose service before the end of 2016. However, T-Mobile has no plan of shutting down their 2G network.

This shutdown is having a notable impact on the electronic security industry, where many 2G GSM radios are in use for alarm signal communication to Central Station dispatch centers. 2G GSM radios must be replaced by newer generation radios to avoid service outages.