Active Node
Active networks, highly programmable networks that perform computations on the user data that is passing through them. As we are describing the Architecture Of Active Node a high-level description of how active nodes might be organized and describe a node programming model that could provide the basis for cross-platform interoperability.
A more extreme view of active networks is one in which every message is a program. Every message, or capsule, that passes between nodes contains a program fragment that may include embedded data. When a capsule arrives at an active node, its contents are evaluated, in much the same way that a PostScript printer interprets the contents of each file that is sent to it. Figure 10 provides a conceptual view of how an active node might be organized. Bits arriving on incoming links are processed by a mechanism that identifies capsule boundaries, possibly using the framing mechanisms provided by traditional link layer protocols. The capsule's contents are dispatched to a transient execution environment where they can safely be evaluated. We hypothesize that programs are composed of "primitive" instructions, that perform basic computations on the capsule contents, and can also invoke external "methods", which may provide access to resources external to the transient environment. The execution of a capsule may result in the scheduling of zero or more capsules for transmission on the outgoing links and/or changes to the non-transient state of the node. The transient environment is destroyed when capsule evaluation terminates.