111//SP193: should be at least ((TCP_WND/PBUF_POOL_BUFSIZE)+1). But that is too small to accommodate data not accepted by the application layer and multiple connections.
112//NETMAN will also always have PBUFs reserved for incoming frames (currently 64).
120//SP193: this should be around the size of the TCP window because the TCPIP thread may take a while to execute (non-preemptive multitasking), otherwise incoming frames may get dropped.