[Synalist] understanding UDP sockets

[S.C.T.N G. <mes...@sc...>]

Hello 
I need help to understand the basic concept of UDP sockets:
I am trying to set up a point-to-point connection between host
A(192.168.2.222:4000)  and host B(192.168.2.224:4000)

 

I am opening the socket like this:

------------------------------------------------------------------

function UDP_trx.s_open(IP,PORT:string):boolean;

begin

    udpsock:=TUDPBlockSocket.Create;

    udpsock.Bind('0.0.0.0',PORT);  // bind socket to local NIC ?

    udpsock.Connect(IP,PORT);     // connect socket to remote IP:PORT ?

end;     

-----------------------------------------------------------------

 

I am sending one byte over the socket (do I need to connect for every
SendByte?)

-----------------------------------------------------------------

procedure UDP_trx.s_tx(txbyte:byte; IP,PORT:string);

var i:integer; s:string;

begin

  //udpsock.Connect(IP,PORT);   // do I need to reconnect every time?

  udpsock.SendByte(txbyte);

end;

-----------------------------------------------------------------

 

And I am receiving one byte over the socket like this:

-----------------------------------------------------------------

function UDP_trx.s_rx(var rxbyte:byte; IP,UDPPRT:string):boolean;

var ipstr:string;  prt:integer;

begin

     if udpsock.WaitingDataEx=0 then begin result:=false; exit; end;

     rxbyte:=udpsock.RecvByte(1);

     //ipstr:=udpsock.GetRemoteSinIP;

     //prt:=udpsock.GetRemoteSinPort;

     //if (ipstr=IP) and (prt=StrToInt(UDPPRT)) then begin result:=true;
exit; end;      //filter for RemoteSin

     result:=true;

end;  

-----------------------------------------------------------------

 

What I do not understand is this: 

Whenever I send a byte to any IP adress (even one that does not exist) I am
receiving a byte at the remote end as long as the port is matching.

Only when I use the s_rx filter with GetRemoteSinIP and GetRemoteSinPort I
can be sure that I receive from the correct source IP.

So I suppose that I have not really understood how to use BIND and CONNECT 

Thank you for help

 

Mit freundlichem Gruß / Yours sincerely / Cordialement

Christian Sporer

 

 

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