Femtocell Reference Interfaces

The above illustration shows a generic femtocell network diagram that includes the main components and identifies the interface references defined by the Femto Forum. A description of the main components that can exist in a femtocell network and the associated Femto Forum–defined reference points is given below;

 The femto access point (FAP) is a hardware device located at the customer’s premise that interfaces with mobile devices over-the air radio interface. The FAP appears to a mobile device as an outdoor macrocell; however, it emits significantly less power. The FAP interfaces with the core mobile network via a broadband interface such as fiber, cable, or DSL. FAPs can support a varying number of mobile devices, typically ranging from four for residential service to eight for small businesses. Using a FAP femtocell to gain access to the mobile network dramatically improves indoor coverage and bandwidth availability for mobile devices. Some FAPs use an Fl interface to control parameters on the broadband access gateway. If a FAP has an integrated access gateway, then the Fl interface is implemented internal to the FAP.
 The femto gateway (FGW) interfaces with the FAP over the broadband access network. This is shown as reference point Fa in the illustration above. The femto gateway performs signaling protocol conversion and in some implementations bearer (voice, video…) channel conversions. The femto gateway also performs the function of a security gateway by protecting the mobile network operator (MNO) from attack attempts over the public broadband access at reference point Fa. The FGW interfaces with the different MNO network segments that have been defined as reference points. Fb-cs is the reference point between the FGW and the MNO’s circuit-switch network for transporting real-time applications such as voice and video. The Fb-ps is the reference point between the FGW and the MNO’s packet-switch network for routing user data such as text messages and e-mail. The Fb-ims interface is used by the FGW to communicate to the core IMS network.
 The subscriber databases are used to store customer provisioning information needed to offer service—information such as the FAP identity and associated settings for provisioning the FAP. The Femto Gateway gets access to the subscribers databases via the Fs and Fr interfaces.
 The femto management system supports two reference points, Fm and Fg. The Fm interface is used to manage the FAP device. The FAP provisioning protocol operates over the IP network between the FAP management system (FAP-MS) and the FAP. FAP vendors and service providers’ management protocols vary; however, they generally provide mechanisms for provisioning as well as reporting of faults. The FAP-MS would be expected to manage tens of thousands of FAP devices. The Fg interface is used to manage the femto gateway; its functions include signaling protocol settings, traffic management settings, codec provisioning options, and fault and alarm processing parameters. The femto gateway management system (FGW-MS) implements the Fg interface and should be able to manage multiple femto gateway devices. FGW vendors and service providers’ management protocols vary; however, they generally provide mechanisms for provisioning as well as reporting of faults.
 The femto application server interfaces to an IMS network at the Fas reference point.