Centripetal Networks sued Cisco Systems for infringing three patents related to network security and packet filtering. The case underwent a bench trial in 2020, where the district court initially found Cisco willfully infringed. However, the judgment was vacated and remanded after the original judge was found to have a conflict of interest due to his wife's ownership of Cisco stock. Following a recusal and reassignment to a new judge, the district court entered a final judgment of noninfringement for the three patents at issue. Centripetal appealed, arguing the district court misinterpreted the patent claims and overlooked evidence of infringement.
The Federal Circuit applied de novo review to claim construction and clear error review to factual findings. Regarding the '193 patent, the court analyzed the specification and prosecution history, which defined a two-stage filtering process. The first stage filters based on source and destination (the 5-tuple rule), while the second stage filters based on the specific method or type of data transfer. The court found that Cisco's quarantine rule only performed the first stage, filtering by source and destination, and did not filter by the specific technique required by the second stage. Centripetal's statements to the Patent Office during an Inter Partes Review confirmed this two-stage requirement. For the '806 patent, the court interpreted the claim term 'responsive to' to require but-for causation. The claims required the device to cease processing packets specifically in response to a signal to swap rules. The court found that Cisco's devices ceased processing during normal idle periods between packets, not as a direct result of the rule-swap signal. Regarding the '176 patent, the claims required the system to automatically generate and provision rules without human intervention. The court found that Cisco's Stealthwatch system only generated alerts for human administrators to review and act upon, failing to meet the automatic generation requirement.
Centripetal's infringement claims for the three patents are dismissed, and the district court's judgment in favor of Cisco stands. The decision clarifies that 'responsive to' in patent claims can require strict but-for causation and reinforces the importance of prosecution history in defining claim scope for two-stage filtering processes. No further proceedings are required on these specific patents.
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