Applying the server-proxy-client 3-tier networking architecture to the mobile network for multimedia transmission is acquiring more attention and effort recently. Proxy servers can improve the transmission quality between wired network and wireless network in the 3-tier networking architecture. However, because of the client's "keeping moving" characteristic, the server-proxy-client architecture must also take user mobility into consideration. We assume that mobile clients should dynamically select a local proxy according to network condition, geographical dependency, and the moving path. In this paper, Application-layer Proxy Handoff (APH) is proposed to have the applications executed smoothly and seamlessly even if mobile clients are moving. The proposed APH employs IPv6 application anycasting technique to resolve how to select the next served proxy. Using the application anycasting technique can not only consider network condition between the mobile client and the nearest proxy, but also achieve load balance among proxy servers in the same subnet. Furthermore, APH provides a session recovery mechanism based on the multicast transmission. The session recovery scheme not only re-constructs the original session on the next served proxy server, but also forwards the unsent media data cached in the original served proxy to the next served proxy.