The introduction of SDN fundamentally changes the way that the
application layer traffic optimization (ALTO) works. This draft
describes two architectures, the Vertical Architecture and the
Horizontal Architecture, allowing coherent coexistence of ALTO and
software defined network (SDN). Unique requirements for design and
operations are identified and summarized, suggesting that the
Vertical Architecture allows better division, management,
flexibility, privacy control and long-term evolution of the network.
We also define the main interactions and information flows, and
present a set of use cases to illustrate how we extend ALTO to
support SDN, in the Vertical Architecture.