Single WireProtocol (SWP) is a standardized interface through which SIM cards communicate with the Near Field Communication (NFC) controller in the smartphone
. The SWP interface is also referred to as the Single Wire Interface because it has only one data and ground wire. Conceptually, it is similar to the I2C bus. The SWP protocol can be used to control NFC applications in the smartphone SIM card. The SWP protocol has been standardized by the European Telecommunications Standards Institute (ETSI).