Live detection is based on lack of response from a site, i.e. timeouts.
Accurate detection, on the other hand, cannot be based on communication since the network is assumed to be asynchronous. The systems research community has long harbored an intuitive notion of what a path is. A fast and general implementation of Mach IPC in a network . For example, Mach is the basis of the NeXTStep operating system, OSF 1, and the GNU Hurd operating system. Another useful property of both SR and Mach is that they are both freely available.