To enable executing a network provided with plural data transfer rates by evaluating the performance of mobile units, scanning the most appropriate access point by means of a set interval, when the performance is lower than a threshold and relating it with the most adequate access point by means of the highest data rate.

When each precise packet response(PPR) is received, the quality of a response signal is evaluated and updated, by measuring a reception signal strength display(RSSI). Appropriate group of the access points lower than the best detection RSSI value is selected, and each mobile unit executes full-scanning and inspects all channels with precision. A prefetching shift for adjusting a dynamic load is enabled in a system, and re-relating with the new access point is enabled. Thus, a possibility in which the mobile unit being unable to communicate with any one of the access points and experiences a period without communication is avoided.