"The best-laid plans of mice and men often go awry" - as the ISO team were designing a beautiful, structured layered model, people were already building their own. Dr Richard G Clegg of Queen Mary University London explains the network layers model. Computerphile is supported by Jane Street. Learn more about them (and exciting career opportunities) at: This video was filmed and edited by Sean Riley. Computerphile is a sister project to Brady Haran's Numberphile. More at