As the name suggests, EDGE (Enhanced Data rates for GSM Evolution), is a technology developed with the basic technology for GSM and GPRS. An EDGE system using devices developed with the remains found on GSM / GPRS network. So can not EDGE alone. A GPRS system is comprised of SGSN (Serving GPRS Support Node) and the GGSN (Gateway GPRS Support Node), which is a network corenya, which added to a previous GSM network. While on the radio, a GPRS network requires the addition of PCU in the previous GSM network radio devices. The figure below shows the general diagram of the GPRS network.
EDGE implementation in the existing GPRS network requires only additions to the radio access side only. While the core network side, EDGE uses the same tools and protocols to those used in previous GPRS networks. GPRS and EDGE network differences found only in akssnya radio side only, while the core network side, EDGE and GPRS using the same tools and protocols. A GPRS network could be upgraded into a network with EDGE system by simply adding an EDGE Transceivier Unit (TRU) on the radio side of the access.
Source : http://id.wikipedia.org/wiki/Enhanced_Data_Rates_for_GSM_Evolution#Implementasi_EDGE