When connecting to the SGSN, a Packet Data Protocol (PDP)
context is created. Think of the PDP context as the connection into the packet network,
each connection being identified by its own unique PDP context.
When connecting from a wireless device to an application server in the IMS domain,
the SGSN/GGSN creates a PDP context for the session and then manages this connection
52 Chapter 2
on the GPRS side. The GGSN then interfaces with the P-CSCF, which provides the
session control within the IMS domain. When connecting to servers and applications,
the GPRS network uses the Access Point Name (APN) for the device to identify which
services it is accessing (based on the server name being connected to).
UMTS and CDMA Domains
The Universal Mobile Telecommunications Service (UMTS) provides broadband packet
services enabling wireless subscribers to use Internet services and other multimediatype
services such as video and multimedia messaging. With a bandwidth of 2 MBps,
UMTS provides the bandwidth required to support some of these services that require
more bandwidth, such as video (IPTV). Voice is also supported through this interface
but is routed from the UMTS nodes to the MSC (the circuit-switched portion of the
network).
As you can see in Figure 2.6, accessing the IMS through a UMTS interface (or any
other access technology for that matter) within a GSM network still involves routing
the packet data through the GPRS SGSN/GGSN nodes.
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