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Figure 3. Basic EPS architecture<br />
The EPS architecture has a similar functional distribution as the HSPA -Direct Tunnel PS core<br />
network architecture. This allows for a very easy integration of HSPA networks to the EPS, as<br />
shown in Figure 4. Reference point S12 between UTRAN and Serving GW is for user plane<br />
tunneling when Direct Tunnel is established. It is based on the Iu-u/Gn-u reference point using<br />
the GTP-U protocol as defined between SGSN and UTRAN or respectively between SGSN and<br />
GGSN. Reference point S4 provides related control and mobility support between GPRS Core<br />
and the <strong>3GPP</strong> Anchor function of Serving GW. In addition, if Direct Tunnel is not established, it<br />
also provides the user plane tunneling.<br />
125 Ericsson. Q2 2007.<br />
www.3G<strong>Americas</strong>.org February 2009 Page 40<br />
125
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