Pros and Cons of Emulating 3G-SGSN

As an alternative to the interconnection of WLAN to 3G-SGSN, it can also
directly be connected to the GGSN of the UMTS network. Figure 2.17
shows the interconnection of WLAN to the GGSN of the UMTS network.
Architecture in Figure 2.17 is a modification to that of Figure 2.13 in
that the interface between WLAN and UMTS is now via a 3G-SGSN–like
device, which is called a 3G-SGSN emulator. The protocol stack is very similar
to the one depicted in Figure 2.14. In this interconnection the Iu interface
and the protocols between 3G-SGSN and 3G-GGSN are not used, and
the functions supported by those protocols are thus not available. It is possible
to bypass some of the RNC-related functions by using a 3G-SGSN emulator,
and mobility management is again handled by UMTS.