This paper demonstrates IP over ATM with congestion avoidance flow control, CEFLAR : Congestion Estimation Feedback by Limited Acceleration-Ratel-Ratio. CEFLAR terminal adapter for STM-I and CEFLAR node are developed to evaluate this characteristic. Experimental results confirm that CEFLAR can avoid the congestion state in ATM networks and control the transmitting rate without upper layer's anomalies, IP packer loss and TCP re-transmission. Fair sharing of the available bandwidth is realized in local area networks. Loss-less transmission on UDP/IP over ATM can be attained even in wide area networks of more than 1000 km in diameter.