Abstract: Nowadays, the schemes of file transfer between smart-phones can be divided into two categories, Internet-based and Ad-hoc-network-based. When the clients connect to the Internet, they can use P2P direct technology or a file server to forward files. Otherwise, WiFi hotspots or Bluetooth technologies are used to set up Ad-hoc networks between clients to realize file transfers. But in the case of network environment changing, the switch between the two schemes will lead to retransmission of files, and the parts that have already been transferred will be wasted. To solve this problem, this article puts forward a file transfer scheme which can adapt to dynamic network environments, choose the optimized route for users, and improve the speed of file transmission.
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Key words:  file transfer, dynamic network, Ad-hoc network, XMPP, automatic switch