sending UDP frames at a fixed rate

I have an application where I would like to send UDP frames at a fixed
rate. (for example, 200 byte frames at 50 frames per second.)
But, using the example above, I may only get 320 frames sent in 10
seconds instead of the 500 I would expect.

I've put GetTickCount()s around the sendto() function to see if that
was taking longer than I would expect, but it always says 0 ms.

The code I'm using to transmit the frames is below. I'd love to hear
any suggestions.

Thanks,
PaulH

    //
    // create an empty buffer to pad the frames to the appropriate
size
    //
    std::vector< char > buffer( 200 );

    //
    // Throw unicast frames at the given rate & size to the DUT
    //
    int totalFrames = static_cast< int >( frames_per_second *
runtime / 1000.0f );
    DWORD dwStartTick = GetTickCount();
    int err = 0;
    const char *pBuf = &buffer.front();
    const int bufSize = static_cast< int >( buffer.size() );

    //
    // Create a timer to send frames at a given rate
    //
    HANDLE hTimer = ::CreateWaitableTimer( NULL, FALSE,
NULL );
    LARGE_INTEGER transmitTime = { 0 };
    transmitTime.QuadPart = static_cast< LONGLONG >(
        -( 10000000.0f / static_cast< float


    const int period = 1000 / frames_per_second;
    ::SetWaitableTimer( hTimer, &transmitTime, period, NULL, NULL,
0 );

    //
    // transmit the test frames
    //
    while( ( err = sendto( dutSocket,
                           pBuf,
                           bufSize,
                           0,
                           reinterpret_cast< SOCKADDR* >( DUTAddr-


                           DUTAddr->ai_addrlen ) ) != SOCKET_ERROR &&
           ( GetTickCount() - dwStartTick ) < static_cast< UINT


    {
        sentFrames++;
        ::WaitForSingleObject( hTimer, period );
    }