Communications Architecture

The figure below shows NetAlive in the context of the Open Systems Interconnect (OSI) model. NetAlive supports two fundamentally different communications paradigms: First, a paradigm based on parallel processing involving one part of an Intertask communicating with another part. Second, a paradigm where NetAlive on one computer accesses non-NetAlive resources located on another computer. An Intertask can use both methods at once.

As a parallel processing language, the Intertask bridges the top of the OSI stack. This view of an Intertask applies when using NetAlive to make an application with multiple GUIs or which explicitly controls multiple computers. Here, several NetAlive system programs work together to interpret one Intertask. Where an arrow connects tasks on different hosts, NetAlive generates an internal message. These NetAlive system programs communicate internally via the path shown in red.

An Intertask can also interact with a remote computer via a protocol such as HTTP, Gopher, FTP, etc. In this case, a NetAlive instance on one computer interacts with a server program on another. Certain tasks access remote resources internally. For example, the HTTP access task takes a URL as input and produces a document as output. The figure shows these paths in green and blue.

NetAlive has both a Winsock and Netscape Client API (NCAPI) interface which it uses under different circumstances. NetAlive uses a variant on HTTP for internal communication, forcing Net Alive! to implement this protocol using its Winsock interface. This protocol extends HTTP to permit loading of an Intertask besides sending data. The figure shows this path in red.

NetAlive generally uses the NCAPI interface for client-server access to remote resources. This path appears in green. NetAlive can access resources via HTTP directly, however, as shown in blue.

NetAlive can operate with Winsock, NCAPI, or both. A configuration dialog lets the user specify which interfaces NetAlive will use. An application will not run when it requires a form of communication that is not available.

NetAlive generally conforms to "industry standards" for interfacing with a Web browser. Vendor implementations are buggy, however, probably because the "standard" is new. The current version of NetAlive (0.0.14) uses the installed Web browser if possible with the built-in Winsock interface as a backup.

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