Try to replace h_t_t_p/1.0 with H_T_T_P/1.1 , but use capital letters, and place / before document name. A generic req. should look like:
GET / H_T_T_P/1.1 . Of course, remove the "_".
Do not request a specific filename, make a request for a generic document, like:
GET / H.T.T.P/1.1 , take the first three points out, and use capitals.
If you specify at the requested URI the "/", the server will return the index document. Try to listen the traffic on port 80 with an ethernet sniffer and see how a standard web browser make this request.