8.6 Local IP Access (LIPA)
The LTE network architecture is designed for the centralized gateways where the operator typically only has one or a few gateways. That architecture makes sense for the Internet access because the number of Internet peering points is limited. Different architecture, however, may be needed for the small base stations to allow access to the local content. The local access would be practical for accessing corporate intranet information or accessing a home network over LTE radio. This section considers the Local IP Access (LIPA) with LTE radio.
LIPA function enables a UE to access directly enterprise or residential network without user plane data travelling first to the centralized gateway. LIPA functionality would make sense together with Home eNodeB (femto). A Local gateway (LGW) is co-located with a femto for the local access. The Local gateway has a subset of P-GW functionalities. The LIPA architecture is illustrated in Figure 8.20. A Home Subscriber Server (HSS) includes information for each APN and for each subscriber whether local access is allowed or not. If local access is allowed, the MME selects the LGW IP address enabling a direct user plane path between the LGW and the Home eNodeB. It is also possible to have multiple PDN connections: one to the macro network PGW and another one to the LGW. An S5 interface is used for controlling the LGW.
LIPA requires the following updates to the network elements. ...