1. A method to query a plurality of Tags, the method comprising: broadcasting through an antenna, one or more first query commands, a first query command of the one or more first query commands including a first value of a probability parameter, the first value of the probability parameter indicating a first level of probability of reply according to which each of the plurality of Tags randomly determines whether or not to reply with handshaking data which comprises a random number, wherein the first value of the probability parameter includes a first number Q, and the probability of reply for one of the plurality of tags includes a second number p based on the first number Q; and detecting a reply in response to the first query command, the reply including the handshaking data comprising the random number generated in response to the first query command, wherein the first query command further includes a state fin indicating a first state, wherein Tags in a second state do not reply to the first query command and Tags in the first state reply to the first query command randomly according to the first value of the probability parameter; broadcasting a second query command including a second value of the probability parameter and a state flag indicating the second state, wherein Tags in the first state do not reply to the second query command and Tags in the second state reply to the second query command randomly according to the second value of the probability parameter; and detecting a reply in response to the second query command, wherein the first and second query commands arc symmetric with respect to the first and second states.