  As the Software Defined Networking (SDN) paradigm gains momentum, every
network operator faces the obvious dilemma: when and how to migrate from
existing IP routers to SDN compliant equipments. A single step complete
overhaul of a fully functional network is impractical, while at the same time,
the immediate benefits of SDN are obvious. A viable solution is thus a gradual
migration over time, where questions of which routers should migrate first, and
whether the order of migration makes a difference, can be analyzed from techno
economic and traffic engineering perspective. In this paper, we address these
questions from the techno economic perspective, and establish the importance of
migration scheduling. We propose optimization techniques and greedy algorithms
to plan an effective migration schedule, based on various techno economic
aspects, such as technological gains in combinations with CapEx limitations. We
demonstrate the importance of an effective migration sequence through two
relevant network management metrics, namely, number of alternative paths
availed by a node on migration, and network capacity savings. Our results
suggest that the sequence of migration plays a vital role, especially in the
early stages of network migration to SDN.
