Lightweight thread tunnelling in network applications

Active Network nodes allow for non-trivial processing of data streams. These complex network applications typically benefit from protection between their components for fault-tolerance or security. However, fine-grained memory protection introduces bottlenecks in communication among components. This paper describes memory protection in Expert, an OS for programmable network elements which re-examines thread tunnelling as a way of allowing these complex applications to be split over multiple protection domains. We argue that previous problems with tunnelling are symptoms of overly general designs, and we demonstrate a minimal domain-crossing primitive which nevertheless achieves the majority of benefits possible from tunnelling.