We have shown that it is possible to fit a full scale TCP/IP implementation well within the limits of an 8-bit microcontroller, but that the throughput of such a small implementation will suffer. We have not removed any TCP/IP mechanisms in our implementations, but have full support for reassembly of IP fragments and urgent TCP data. Instead, we have minimized the interface between the TCP/IP stack and the application.
The maximum achievable throughput for our implementations is determined by the send window size that the TCP/IP stack has been configured to use. When sending data with uIP, the delayed ACK mechanism at the receiver lowers the maximum achievable throughput considerably. In many situations however, a limited system running uIP will not produce so much data that this will cause problems. lwIP is not affected by the delayed ACK throughput degradation when using a large enough send window.