2.5G networks offer some improvements over 2G networks but are not quite as fast as 3G networks. They use a circuit-switching domain for voice communication and a packet-switching domain for data communication. This set of standards enables high-speed data transfer over existing 2G GSM or CDMA networks that have been upgraded, and it usually describes when a 2G network has been upgraded with GPRS for data transmission. Technologies that are directly related to 2.5G are GPRS, EDGE, and iDEN.
GPRS
The first improvement in mobile data transmission, Generated Packet Radio Service (GPRS), can be added to 2G, GSM, or 3G networks. GPRS achieves moderate improvements in data transmission by using TDMA to improve packet switching over the mobile network. As with many other technologies, after its initial deployment, GPRS technology was later integrated into GSM.
EDGE
Enhanced Data Rates for GSM Evolution (EDGE) was launched in the United States by Cingular in 2003. Through optimization of packet switching, it provides better than a threefold improvement over other networks in capacity and performance of data transmission, making mobile computing and data transmission much more valuable. Sometimes referred to as 2.75G, EDGE improved the rate of data transmission over GSM networks. Although it was originally intended for GSM, it can be added to 2G, 2.5G, and GPRS networks as well.
iDEN
Integrated Digital Enhanced Network (iDEN) combined voice compression with TDMA to improve on 1G radio telephony. It is a proprietary subset of 2G technology developed by Motorola and used by Nextel in the United States and Telus in Canada. The technology is important for Nokia and Telus because it allows for push-to-talk radio and dispatch functionality that enables mobile phones to be used as long-range walkie-talkies. Many airports also use iDEN networks to enable their push-to-talk handsets.
