In its Judgment on the dispute between Sony Communications and SSH Communications the UK High Court has deemed invalid patent EP(UK) 2254311 which relates to the use of keepalive packets.

The invention under consideration relates to ensuring that the IPsec protocol suite could be used reliably and securely through Network Address Translation (NAT). At issue was whether Sony’s Xperia phone would infringe the patent when using internet calling.

Around the priority date of the patent work was under way to deal with the proliferation of computers and other devices connecting with the internet. At the heart of the problem was the finite number of possible IP addresses provided by the Internet Protocol IPv4.

To give some background to the field Network Address (and port) Translation (NAT) solves the IPv4 addressing problem by permitting devices in a private network to have a private address which may be the same as an internal address in another network. A NAT device, usually incorporated in a router, maps private internal addresses to an external address (and port number) and stores the mapping in a mapping table maintained in the NAT device. After a period of inactivity mapping is no longer maintained to avoid internal memory of the NAT device being filled with obsolete data. This causes problems where an application is running but has not generated data within a timeout period. If the transport control protocol (TCP) is used, an address could look for a FIN message to drop a mapping. However, for a use of the user datagram protocol (UDP) there is no such termination indication to utilise.

The invention proposed the sending of keepalive packets frequently enough that a useful address translation remained cached.

The Judgment provides an insight into the interpretation of how obviousness over common general knowledge (CGK) alone should be judged. CGK is the technical background to the notional skilled person against which the prior art should be considered. The judgment reiterated that this does not mean everything on the shelf which is capable of being referred to without difficulty is CGK nor that every word in a textbook is either. The skilled person reads each specific piece of prior art with his CGK but does not read a specific citation with another specific citation in mind unless the first causes them to do so. Use of keepalives for various applications were deemed CGK but the documents indicating that people were using keepalives themselves were not.

The Judgment also reiterated that a lack of a starting point for the assessment of obviousness is a particular problem with obviousness over CGK as such a starting point is not encumbered with inconvenient details of the kind found in documentary disclosures such as misleading directions. Lack of a starting point makes it impossible to apply the Pozzoli questions, particularly the third question which can itself indicate a fatal flaw in an attack based solely on CGK.

A key prior art reference considered was the question and answer notes, minutes and associated guidelines from a meeting of the 43rd IETF NAT Working Group. These were cross referenced so that they could be read together for prior art purposes. It was found that a statement from the audience was deemed highly relevant to the extent that overall the disclosure anticipated the key claims of the patent. The Patent was thus ruled invalid.

The Judgment went on to consider if SIP messages, sent over the control channel associated with internet calling using Sony’s Xperia phones, are keepalives. The conclusion was that SIP OPTIONS messages are generally sent solely for the purpose of renewing timeout of a NAT. As such it was ruled that key claims were found infringed.

In summary, it is key for clients to understand the need to file patent applications prior to any detailed group discussions. Attorneys need to consider the complexities of raising CGK based validity attacks.