Hi;
I agree with kunal.Many of the TCP/IP features are not really needed for an instrument network.Stuff like fragmentation and reassemebly can be left out to reduce the code and ram usage.Also another troublesome thing is ARP.if the instruments are going to have known MAC ID then you can leave out that part too.CMX micronet specfication is a way to go if somebody wants to implement a stack of his own.
Also for a typical TCP/IP implementation put jim brady TCP/IP in google.one can find link to circuitcellar site and a fantastic article.
Pranav