Sony Communications International AB v SSH Communications Security Corporation

A keepalive packet is construed by reference to its technical purpose: maintaining a network address and port mapping through a network address translator. It may contain meaningful information and need not be limited to a packet carrying no meaningful payload. A claim requiring determination of the shortest timeout period does not require accurate measurement. An approximation is sufficient if it establishes a period shorter than the relevant timeout.

For obviousness, common general knowledge must be assessed as the stock of knowledge informing the skilled person from the outset. Information which could be found by a search is not necessarily common general knowledge. An attack based on common general knowledge alone requires an identifiable starting point before the Pozzoli questions can properly be applied.

Sony sought revocation of SSH’s European patent concerning the maintenance of address translations for datagram communications through network address translators. SSH counterclaimed for infringement by Sony Xperia devices and proposed three sets of conditional amendments.

The principal construction issues concerned the meaning of a keepalive packet and the requirement in claim 6 to determine a shortest timeout period. The court also considered validity over common general knowledge and two documents relating to NAT design, and made conditional findings on infringement.

1. Construction. A keepalive packet is a packet repeatedly transmitted for the purpose of maintaining the IP address and port mapping at the NAT. The expression is not confined to packets containing no meaningful data. The packet may contain meaningful information, provided it performs the relevant keepalive function.
2. The requirement to determine a shortest timeout period does not require accurate determination of the actual timeout. A rough determination, including one obtained by trial and error, is sufficient if it establishes a period shorter than the timeout and results in keepalives being sent frequently enough to preserve the mapping.
3. Amendments. The conditional amendments did not cure the invalidity. The court rejected the suggested confusion between disclosure and coverage, applying the distinction identified in AC Edwards v Acme [1992] RPC 391 and AP Racing v Alcon Components [2014] EWCA Civ 40. The third amendment was sufficiently disclosed because the skilled person would understand that the specification permitted multiple keepalives within 30 seconds.
4. Obviousness. The court applied the Pozzoli questions. The common general knowledge relied upon did not establish a sufficient starting point for the attack based on common general knowledge alone. The warning in Ratiopharm v Napp [2009] RPC 11 was material. The Minutes and Guidelines, read together, clearly disclosed the use of keepalives to prevent NAT timeouts affecting UDP communications. Claims 1 and 2 were anticipated. The remaining claims, including the product claims, were obvious because their additional features would have been obvious to the skilled addressee.
5. Infringement. Although all claims were invalid, the Xperia devices would have infringed claims 1, 3, 6, 8, 10 and 13 as granted and in the proposed amended forms, if valid.