http://www.rfc-editor.org/rfc/rfc6429.txt
RFC 6429: TCP Sender Clarification for Persist Condition, M. Bashyam, M. Jethanandani, A. Ramaiah2011-12-01T23:00:00-00:00This document clarifies the Zero Window Probes (ZWPs) described in RFC 1122 ("Requirements for Internet Hosts -- Communication Layers"). In particular, it clarifies the actions that can be taken on connections that are experiencing the ZWP condition. Rather than making a change to the standard, this document clarifies what has been until now a misinterpretation of the standard as specified in RFC 1122. This document is not an Internet Standards Track specification; it is published for informational purposes.