When wireless networks as connected to wired networks, e.g. ATM networks, mobile hosts can gain access to the resources stored on the wired networks. Handoffs originally used in wireless networks must be extended if the wired network is connection-oriented, such as ATM. In the new environment, if a mobile host is moving out of its current cell, radio signals and connections must be switched accordingly. For a seamless handoff, the related operations must be performed with low latency, minimal cell loss and no change in the cell sequence. In this paper, we propose a cluster structure to link wireless networks to ATM networks, which can greatly reduce the handoff delay and improve performance. The performance of this method is analyzed and studied in simulation, which shows that it is superior to other methods