The Serving GPRS Support Node (SGSN) and the Gateway GPRS Support
Node (GGSN) both support the role of controlling the data transfer to other packet
networks.
The GPRS protocol is obviously different than SS7, which does not support packet
services. The GPRS protocol and its associated interfaces support connectivity to the
various SGSN/GGSNs within a wireless network, and the control of those connections
(referred to as Packet Data Protocol [PDP] contexts).
Yet GPRS answers the needs for supporting packet service in the core, and not the
air interface. With the addition of messaging and video services came the need for more
bandwidth at the air interface, and thus UMTS was created. The UMTS network only
covers the air interface consisting of new radio functionality interfacing back into the
traditional GSM network as well as the GPRS packet network.
There are other similar technologies that enable bandwidth at the air interface in
support of broadband services. Code Division Multiple Access (CDMA) 2000 is one example,
as is Enhanced GPRS. Ultimately, SIP will become the standard across-the-air
interface as well, once mobile devices have been SIP-enabled.
The IMS extends all of these capabilities using SIP as the primary session control once
the session reaches the IMS domain. Eventually, handsets will be equipped with SIP capability
and will perform as SIP user agents.
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