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Overview
The Femto Application Platform Interface (FAPI) is an initiative within the femto industry to encourage competition and innovation between suppliers of platform hardware, platform software and application software by providing a common API around which suppliers of each component can compete. In doing this, we imitate a long and distinguished engineering tradition of providing an “interchangeability of parts” to ensure that the systems vendors can take advantage of the latest innovations in silicon and software with the minimum of entry barrier, and the least amount of custom re-engineering.
The FAPI is defined via a reference architecture shown below, which is generic to 3G or 4G femtocells. Several APIs are defined, as follows:
P1 – the Security coprocessor interface
P2 – the Service Discovery Interface
P3 – the GPS interface
P4 – the Network Listen Results interface
P5 – the PHY mode control interface
P6 – the ciphering coprocessor interface
P7 – the main datapath interface
M1 – the scheduler interface

Currently public APIs are available for LTE femtocells, but others have been defined for 3G applications.
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