Near Field Communication (NFC) is the standard for short distance (up to 10 cm) contactless data exchange. The technology is a simple extension of the ISO/IEC 14443 proximity-card standard (contactless card, RFID) that combines the interface of a Smart Card and a reader into a single device. An NFC device can communicate with both existing ISO/IEC 14443 Smart Cards and readers, as well as with other NFC devices, and is thereby compatible with existing contactless infrastructure already in use for public transportation and payment. NFC is primarily aimed at usage in mobile phones. Newest inventions allow the customer to use their mobile phone, due to NFC, as virtual entrance card or to pay with it by holding it closely to a till.
NFC devices are able to communicate with Smart Cards, readers and other NFC devices. They can receive and send data simultaneously and therefore have the ability to check the received radio frequency field and detect a collision if the received response does not match with the expected signal. In the field of mobile phone technology where the NFC devices are used, three main modes are distinguished: