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UBC Theses and Dissertations

An experiment in high level protocol design Scotton, Geoffrey Richard


High level communication system design is of increasing interest as the interconnection of computer systems becomes more widespread. High level communication, systems provide users/applications with a convenient virtual communication environment that is an abstraction of the underlying transport communication mechanism. Examples include high level protocol support for file transfer, virtual terminal and mail delivery applications. We describe the implementation of communication software support for the ITI virtual terminal protocol using an existing X.25 protocol implementation. The design and implementation of a high level communication system using an experimental research computer system is described within this thesis. We also present a design that is a generalization of the model implemented and compare this with other communication models, notably the ISO Open Systems Interconnection model and the Xerox Pup internetwork architecture. In particular we address the following issues: (a) Dynamic protocol layer initiation from an incoming call. (b) Utilization of a uniform interface between protocol layers and at the user interface. Within the implementation described this is achieved using an interprocess message based I/O protocol. (c) The suspension of higher layers and application processes after a transport level failure and the subsequent reconnection when the transport connection is re-established. The design utilizes layered communication modules that provide external (high level) protocol support or alternatively may provide local services and functions such as local data transformation and reconnection functions. The utilization of a uniform interface between modules and at the user interface allows the liberal interconnection of modules to provide the required communication services with a minimum of overhead.

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