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Ph.D. Thesis

Yoram Ofek

Department of Electrical and Computer Engineering University of Illinois at Urbana-Champaign, May 1987.



To Barbara, and our Children: Tidhar, Gidon, and Daphna; and Maya who came later

The complete pdf file of Ph.D. Thesis can be found here.

List of chapters of Ph.D. Thesis:


One of the main challenges in computer engineering today is the question of how to connect a large number of computing nodes, which are distributed over a large area, into one integrated system. The functions performed by the system are varied from electronic mail, distributed file servers to parallel processing, and real-time data communication (e.g., voice and video).

The research, presented in thesis, involves a bottom-up design of a fiber optic hypergraph network. The network is constructed of nets, which are passive optical stars, and constitute a multiple access medium. The topology and the high bandwidth (>1 gigabit/second) enable the construction of a low-dimension, synchronous, hypergraph network. The system maintains a global event synchronization with total ordering and uniformly integrates various functions by using distributed algorithms. It will be shown how voice and data are integrated on the system and how time stamps are used for implementing concurrency control algorithms (e.g., mutual exclusion). These algorithms are designed for a real-time operation in a very high bandwidth.

The following new ideas were incorporated:

  • a new family of conservative codes, for preserving time integrity and decoding, without a phase-locked loop,
  • a hierarchical interface to one gigabit/second serial link,
  • a protocol for periodic exchange of state and time information, which enables the implementation of a hybrid multiple-access control scheme, and the integration of other network control functions,
  • an algorithm for maintaining global event synchronization and total event ordering,
  • a scheme for integrating voice and data by constructing virtual multiplexers and demultiplexers,
  • an isolate and skip mechanism for graceful degradation of the network performance, and
  • a partial hypergraph as a centralized switch.

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