[lwip-users] LWIP configuration to maximize TCP throughput given RAM constraints

[Bruce Sutherland]

Hi everyone.

We are using lwip on an embedded target (LPC2368 microcontroller).

We have successfully used lwip to act as a serial device server. That is to
say, we accept data via a TCP connection on an Ethernet link, and transmit
the data out on an RS-232 serial port.

Now, our goal is to maximize throughput over the link. My impression is that
maximum TCP throughput is limited by lwip configuration options. These
options are mostly constrained by the available memory. This means that
maximum throughput is some function of memory size, capped by any other
bottlenecks in a system, something like this:

http://er6australia.com/images/tcp_thruput_vs_memory.png

My question is: given a certain amount of free RAM, how should lwip options
be configured for best throughput?

Say for example, we have 10 kb of RAM available for lwip to use. How should
we set options such as MEM_SIZE, MEMP_SANITY_CHECK, MEMP_OVERFLOW_CHECK,
TCP_WND, TCP_QUEUE_OOSEQ, TCP_MSS and so on? I know this is quite a broad
question. Links to discussions of this subject would be welcomed.

Regards,

Bruce.