Robocopy is the best option for copying files in this case. Robocopy has functionality to tolerate connection failure and still resume copying.
Robocopy, for "Robust File Copy", is a command-line directory and/or file replication command for Microsoft Windows. Robocopy functionally replaces Xcopy, with more options. Created by Kevin Allen and first released as part of the Windows NT 4.0 Resource Kit, it has been a standard feature of Windows since Windows Vista and Windows Server 2008. The command is robocopy.