TCPIP_UDP_SOCKET_DEFAULT_TX_QUEUE_LIMIT Macro

#define TCPIP_UDP_SOCKET_DEFAULT_TX_QUEUE_LIMIT 3 

The maximum number of TX packets that can be queued by an UDP socket at a certain time. For sockets that need to transfer a lot of data (Iperf, for example), especially on slow connections this limit prevents running out of memory because the MAC/PHY transfer cannot keep up with the UDP packet allocation rate imposed by the application. Adjust depending on the TCPIP_UDP_SOCKET_DEFAULT_TX_SIZE, the connection speed and the amount of memory available to the stack.