The layered architecture used in large data communication networks provides modularity at the expense of efficiency. This paradigm has been successful in wired and many wireless networks. Modularity simplifies the design of large heterogenous and complex networks via a "divide-and-conquer" approach, decoupling an enormously difficult problem into tasks that can be pursued independently. Because of this, new applications can be developed independently of the medium access and routing strategies specified at lower layers, and new physical layer techniques can be implemented without changing upper layer implementations. Perhaps the most remarkable feature of the layered architecture is that it makes the network design scalable. A prime example is the Internet, which has grown from a hand full of nodes in the ARPAnet to hundreds of millions of nodes today.
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