The selected solution for LIPA works as follows: (Reference http://www.3gpp.org/ftp/specs/html-info/23829.htm )
To get access to devices on a local network to which a femto is connected to, the mobile device can use a special APN. The APN tells the SGSN (UMTS) or the MME (LTE) that the mobile device wants to get a connection to the local network and not to the network operator’s core network. Optionally, a LIPA flag is defined that can be sent by the mobile device during the PDP context establishment (UMTS) or the Default Bearer activation (LTE) for the same purpose (This requires some additional software in the mobile device).
For simultaneous access to the local network and the Internet, two solutions are given in the TR -
First, the mobile could have two PDP contexts (UMTS) or two default bearers (LTE), one that terminates in the local network and one that goes through the core network to the GGSN/P-GW.
Also the TR specifically says that the in case Internet connectivity is available through the local network, LIPA does allow the UE to reach the Internet this way. This might be desirable in many cases as it nicely offloads Internet traffic as well but has some consequences for IP based network operator services such as MMS as these can’t be reached that way.
TR specifies a (logical) Local Gateway (L-GW) in the femtocell that acts as a GGSN (UMTS) or P-GW (LTE). Once the LIPA PDP context / default bearer is established data flows directly to the L-GW and from there into the local network without traversing the radio access network or the core network of the network operator.
I hope this will clarify the doubt about the call-flow.
