Ethernet, wireless LAN, ADSL, cable modem, and dialup are common access networks that have dramatically different characteristics. Fast and accurate classification of access networks can benefit a wide range of applications. In this paper, we propose a simple and efficient end-to-end scheme to classify access networks into three categories: Ethernet, wireless LAN and low-bandwidth connection. Our scheme is based on the intrinsic characteristics of the various access networks, and utilizes the median and entropy of packet-pair inter-arrival times. Extensive experiments show that our scheme obtains accurate classification results in a very short time (95% accuracy in 2s, with 10 packet pairs).