US Patent 9705775 Passive performance measurement for inline service chaining

A method is implemented by a network device to monitor the performance of packet processing in an in-line service chain, the network device one of a plurality of network devices forming a software defined network (SDN) and the in-line service chain. The SDN includes a controller to configure the plurality of network devices. The method includes receiving a sequence of packets of a data flow traversing the in-line service chain, applying a hash function to the sequence of packets of the data flow to generate a set of hash values for the sequence of packets, and sending the set of hash values and a set of timestamps for the sequence of packets to the controller to determine delay and loss across a service of the in-line service chain.