I'm not expert on the subject and i never designed a TCP/IP for microcontrollers (YET!) but lets assume you want to design air conditioning unit for a huge hall and the rich man offered you big bucks to reuse his 20 old small air conditioning units in his store to save money. The other requirement would be to be as energy friendly as possible how would you do it?
One good way of doing it would be to put a microcontroller and temperature sensor next to each unit and space the units equally in the huge hall and make TCP/IP connection between them to make them all communicate with each other to know the temperature in each ones area then some can be switched on while others can be switched off giving very tight temp management and control over the whole hall area.
Hope this helps
Good Luck