  Middleboxes are increasingly deployed across geographically distributed data
centers. In these scenarios, the WAN latency between different sites can
significantly impact the performance of stateful middleboxes. The deployment of
middleboxes across such infrastructures can even become impractical due to the
high cost of remote state accesses.
  We introduce Constellation, a framework for the geo distributed deployment of
middleboxes. Constellation uses asynchronous replication of specialized state
objects to achieve high performance and scalability. The evaluation of our
implementation shows that, compared with the state-of-the-art [80],
Constellation improves the throughput by a factor of 96 in wide area networks.
