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procedure TForm1.Button1Click(Sender: TObject);
begin
IdTCPServer1.DefaultPort:=80;
IdTCPServer1.Active:=true;

IdTCPClient1.Host:='127.0.0.1';
IdTCPClient1.Port:=80;
IdTCPClient1.Connect(IdTCPClient1.ReadTimeout);
end;					

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procedure TForm1.idTCPServer1Connect(AThread:TidPeerThread);
begin
 AThread.Connection.WriteLn('Hallo, ich bin '+idTCPServer1.LocalName);
end;

{...}

begin
 ShowMessage(idTCPClient1.ReadLn);
end;					

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procedure TMainForm.POPServerExecute(AThread: TIdPeerThread);
var uMsg,Msg:string;
begin
 with AThread.Connection do try
  Msg:=ReadLn;
  if length(Msg)=0 then exit;
  uMsg:=UpperCase(Msg);

  if copy(uMsg,1,5)='USER ' then begin
   WriteLn('Hallo '+copy(Msg,6,length(Msg));
  end else
  if {..} 
  else WriteLn('Fehler bei Befehlverarbeitung: '+Msg);
end;