GPRS is explained in the next section, but it provides an overlay network
supporting various data services such as Internet access, video and audio support, and
other packetized services.
General Packet Radio Service (GPRS)
The GPRS network works as an overlay to the existing GSM network. All packet data
received from a GSM handset is routed from the base station controller (BSC) to the
Serving GPRS Support Node (SGSN). The SGSN is a packet data node supporting
multiple media types in a packet network.
As shown in Figure 2.5, the SGSN provides connectivity to other SGSNs within the
same network, acting as the packet data network for the wireless operator. None of
this traffic is routed through the Mobile Switching Center (MSC), since this switch is
designed to support voice.
To interface to external packet networks, the Gateway GPRS Support Node (GGSN)
is used. The GGSN provides connectivity to other packet networks, including other
wireless carriers??™ GPRS networks. This overlay network then provides complete packet
data support within a wireless environment within the core network, but this does not
extend to the air interface. Other technologies exist to provide support of packetized
broadband services at the air interface.
The GPRS network provides and manages connections to packet networks. This
means that GPRS must provide some fashion of session control for each of the connections
within its domain.
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