NDK2.0 TCP/IP Receive Window question.

Hi Anatoly,

It sounds like you are wondering how to configure some socket timings.  A few things I can think of are the keep alive probe times, keep idle times and send and receive timeouts.

To configure the send and receive timeouts, you can do this when creating a socket by setting the socket options SO_SNDTIMEO and SO_RCVTIMEO (see 'getsockopt()' API in NDK Programmer's Guide).

To configure the others, you would need to do this at run time via the NDK configuration infrastructure

        Int keepIdleTime = 100; // change to value you want ...
        CfgAddEntry(hCfg, CFGTAG_IP, CFGITEM_IP_TCPKEEPIDLE,
                CFG_ADDMODE_UNIQUE, sizeof(uint), (UINT8 *)&keepIdleTime, 0);

        Int keepProbeInterval = 100; // change to value you want ...
        CfgAddEntry(hCfg, CFGTAG_IP, CFGITEM_IP_TCPKEEPINTVL,
                CFG_ADDMODE_UNIQUE, sizeof(uint), (UINT8 *)&keepProbeInterval,
                0);

        Int keepProbeTimeout = 100; // change to value you want ...
        CfgAddEntry(hCfg, CFGTAG_IP, CFGITEM_IP_TCPKEEPMAXIDLE,
               CFG_ADDMODE_UNIQUE, sizeof(uint), (UINT8 *)&keepProbeTimeout, 0);

For more info, please again refer to the NDK Programmer's Guide, in Chapter 4 "Initialization and Configuration."

Steve

Thank for the information.

I referred to the user guide, and got that there is an option to set a value to receive/transmit buffers of the TCP.

But actually, I wonder how to configure the TCP Receive Window in the NDK?

Anatoly.

Hi Anatoly,

Yes, I believe you need to configure the TCP receive buffer size.

By definition, the TCP receive window is the amount of free receive memory available for the connection (the socket buffer).  The socket receive buffer size for a TCP socket is set by the TCP receive buffer.  So initially, the window size would be the size of the TCP receive buffer.  Then, as data is received, the window size shrinks to be the amount available in the buffer.

Looking at the TCP receive code (tcpin.c line 353), we can see the window size calculation comes from the size of the receive buffer (hSBRx):

 // Get our receive window (function should not return <0, but
 // check anyway). We also know our window can not shrink.
 // (We can not reduce the size of an allocated receive buffer).
 win = SBGetSpace( pt->hSBRx );
 if( win < 0 )
 win = 0;
 else if( win > TCP_MAXWIN )
 win = TCP_MAXWIN;

Steve

Isn't the receive window of TCP the size on which the protocol expects to receive acknowledges from the remote host?

I mean, if I set the receive window 5K for TCP, so the protocol app will receive an acknowledge only after 5K of data is being received on the side of the host. Am I wrong with the definition?

Anatoly.

Anybody have a clue?

Thank you.

Regards, Anatoly.