It defines two types of contactless cards ("A" and "B")[6] and allows for communications at distances up to 10 cm (3.9 in)[citation needed]. There had been proposals for ISO/IEC 14443 types C, D, E, F and G that have been rejected by the International Organization for Standardization. An alternative standard for contactless smart cards is ISO/IEC 15693, which allows communications at distances up to 50 cm (1.6 ft).