misunderstanding of TCP/IP in a gen_server

[info]

Hello,
I have a problem of TCP/IP understanding.
I set the socket server like this:
Opts = [binary, 
             {reuseaddr, true},
             {backlog,5}, 
  {packet, 0},  
  {active, false},
             {nodelay, true}], 

and, after the listen and the accept, I do:

case gen_tcp:recv(Socket, 0) of
        {ok, Data} ->

I monitor the TCP/IP frames and I see (client  ->  server):
AP ->               
<- AF 
->  A
->  AR

I don't understand why the server set the flag "F". The consequence is the reset (AR) by the client.

J-Ph. Constantin
ITS3 Genève
www.its3.ch