Radio waves are the carriers of data between the reader and tags. The approach generally adopted for RFID communication is to allocate frequencies depending on application. The frequencies used cover a wide spectrum. These specified bands are: Low Frequency (LF) 125 - 135 kHz High Frequency (HF) 13.56 MHz Ultra High Frequency (UHF) 400 -1200 MHz Microwave 2.45 and 5.8 GHz The allocation of frequencies is regulated by government agencies, requiring care in considering RFID applications in different countries. Efforts at standardization should avert these problems. The many varied applications will work their best at different frequencies, therefore, it is important to understand the requirements before selecting a particular type of RFID system. The most common uses of low frequency systems are in security access, asset tracking and animal identification. They generally have short reading ranges and lower system costs. High-frequency systems are used for such applications as railroad car tracking and automated toll collection. They offer long reading ranges and high reading speeds. This higher performance usually entails higher costs. The power level of the interrogator and the power available within the tag to respond will determine the reading range that can be achieved in an RFID system. Like the restrictions on carrier frequencies there are legislative constraints on power levels. Environmental conditions, particularly at the higher frequencies, can also influence the range of communication.