To ensure that we can all watch YouTube without interruption, major Internet service providers must manage two very different switching technologies. Wide area "IP" networks made up of packet switches are interconnected over long distances by circuit-switched "transport" networks. Past efforts to bridge packet-based and circuit-based technologies have approached the problem with the assumption that the two networks, which have very different architectures, must remain distinct. As a result, trying to span the two networks has resulted in very complex solutions.

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