We have all known the existence of GSM and CDMA techniques of mobile communication. Many would know that CDMA is Code Division Multiple Access but only a few would know the technique used by GSM. Actually GSM doesn't refer to the name of a technology like CDMA does. GSM stands for Global System for Mobile communication which is a set of rules agreed upon by several countries and companies. GSM uses the technology called as TDMA. The expansion of TDMA is Time Division Multiple Access. In TDMA the data packets are all sent in a round robin manner based on the time allotted. Equal time periods are allotted and the data packets can be sent only during those time periods.