GERAN is the radio part of GSM/EDGE together with the network that joins the base stations (the Ater and Abis interfaces) and the base station controllers (A interfaces, etc.) The network represents the core of a GSM network, through which phone calls and packet data are routed from and to the PSTN and Internet to and from subscriber handsets.
:"to support the market for voice communication and related voiceband communication (such asfacsimile) between users . . . to ensure that users connected to IP based networks can communicate with users in Switched Circuit Networks (such as PSTN/ISDN and GSM), and vice versa."