  Network monitoring and measurement are crucial in network management to
facilitate quality of service routing and performance evaluation. Software
Defined Networking (SDN) makes network management easier by separating the
control plane and data plane. Network monitoring in SDN is lightweight as
operators only need to install a monitoring module into the controller. Active
monitoring techniques usually introduce too many overheads into the network.
The state-of-the-art approaches utilize sampling method, aggregation flow
statistics and passive measurement techniques to reduce overheads. However,
little work in literature has focus on reducing the communication cost of
network monitoring. Moreover, most of the existing approaches select the
polling switch nodes by sub-optimal local heuristics. Inspired by the
visibility and central control of SDN, we propose FlowCover, a low-cost
high-accuracy monitoring scheme to support various network management tasks. We
leverage the global view of the network topology and active flows to minimize
the communication cost by formulating the problem as a weighted set cover,
which is proved to be NP-hard. Heuristics are presented to obtain the polling
scheme efficiently and handle flow changes practically. We build a simulator to
evaluate the performance of FlowCover. Extensive experiment results show that
FlowCover reduces roughly 50% communication cost without loss of accuracy in
most cases.
