  Network Function Virtualization (NFV) and Service Function Chaining (SFC)
have been widely used to enable flexible and agile network management. To
enhance reliability, some research has proposed to deploy backup function
instances for prompt recovery when a primary instance fails. While most of the
recent studies focus on speeding up recovery, less attention has been paid to
the problem of minimizing the state update cost. In this work, we present
PiggyBackup (Piggyback-based Backup), an efficient backup instance deployment
and update protocol. Our key idea is to reuse the existing service chains
traversing through servers in a network to help piggyback the update
information. By doing this, we eliminate the header overhead and reduce the
amount of update traffic significantly. To realize such a piggyback-based
update more efficiently, we investigate the backup instance deployment and
chain selection problems to enhance piggybacking opportunities and reduce the
forwarding hop counts with explicit consideration of the distribution of
service chains. Our simulation results show that PiggyBackup reduces the
average overall update overhead by 47.65% and 39.56%, respectively, in a
fat-tree topology as compared to random deployment and shortest path based
deployment.
