how to xmt 270Mb/s serial data with other data

my question is below :

at xmt port,the 270Mb/s serial data is oversampled and made serial-parellel to 10bit parallel data,and then I transmitter it with other data,like control and ethernet . at rcv port , I must do 10bit parallel to serial process to reconstruct the original 270Mb/s serial data. but this serial data is not sync with transmitter clock.so my fifo always overflow or empty? I donot know how to do?