This thesis presents the development and implementation of a token bus protocol for a Power Line Local Area Network (PLLAN) which utilizes intra-building power distribution circuit as the physical transmission medium. This medium provides a low cost means for data communications with a high degree of portability. Due to the characteristics of the power line and the prototype modem, the network would be easily saturated with data and would have a high collision probabilities. The IEEE 802.4 token bus standard is modified to fit the PLLAN and to bring its performance up. A comparative performance of the original protocol and the modified version shows that the latter provides an improvement in network throughput of up to 15 percent and a reduction in the network join-ring delay of up to 20 percent for a wide workload range. The performance figures of the modified version in a power line network of three SUN 3/50 workstations¹ transmitting at 9.6 kilo-bit per second is also presented and analyzed. ¹Sun workstation is a trademark of Sun Microsystems. / Science, Faculty of / Computer Science, Department of / Graduate

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This dissertation describes the design and implementation of the file system component of the Saguaro operating system for computers connected by a local-area network. Systems constructed on such an architecture have the potential advantage of increased file availability due to their inherent redundancy. In Saguaro, this advantage is made available through two mechanisms that support semi-automatic file replication and access: reproduction sets and metafiles. A reproduction set is a collection of files that the system attempts to keep identical on a "best effort" basis, relying on the user to handle unusual situations that may arise. A metafile is a special file that contains symbolic path names of other files; when a metafile is opened, the system selects an available constituent file and opens it instead. These mechanisms are especially appropriate for situations that do not require guaranteed consistency or a large number of copies. Other interesting aspects of the Saguaro file system design are also described. The logical file system forms a single tree, yet any file can be placed in any of the physical file systems. This organization allows the creation of a logical association among files that is quite different from their physical association. In addition, the broken path algorithm is described. This algorithm makes it possible to bypass elements in a path name that are on inaccessible physical file systems. Thus, any accessible file can be made available, regardless of the availability of directories in its path. Details are provided on the implementation of the Saguaro file system. The servers of which the system is composed are described individually and a comprehensive operational example is supplied to illustrate their interation. The underlying data structures of the file system are presented. The virtual roots, which contain information used by the broken path algorithm, are the most novel of these. Finally, an implementation of reproduction sets and metafiles for interconnected networks running Berkeley UNIX is described. This implementation demonstrates the broad applicability of these mechanisms. It also provides insight into the way in which mechanisms to facilitate user controlled replication of files can be inexpensively added to existing file systems. Performance measurements for this implementation are also presented.

This dissertation is concerned with the design of a high speed fiber optic campus backbone network which not only provides a high bandwidth connection to various LANs, PBXs, ISDNs, supercomputers, and other high speed computing facilities but also offers an integrated service of voice and data. The campus backbone network is based on an optical fiber dual ring structure. A new token ring protocol based on the IEEE 802.5 standard is proposed as the medium access protocol for the backbone network. In the proposed token ring network, the token holder transmits packets in an exhaustive way when no other nodes want to transmit voice packets. If any node has voice packets waiting for transmission, the token holder can transmit only a single packet during its access opportunity. In this way, not only can the voice delay be bounded at high voice traffic intensities, but a high data throughput can be achieved at low voice traffic intensities. The potential use of Time Division Multiplexing (TDM) was also considered, but the TDM technique was found to be less suitable for our campus environment mainly due to its low efficiency in bursty environments and complex hardware requirements. The backbone network was simulated using the Simscript II.5 discrete event simulation language. The simulation results indicated that the proposed token ring protocol provides satisfactory performances in every respect. A network interface unit (NIU) was designed, which consists of optical transmitter, receiver, and fault tolerance mechanisms as well as the protocol engine. The optimal values of major parameters for the NIU design were determined by the simulation.

This dissertation describes the analysis, design, and implementation of a session level communication system referred to as PLEXNET. PLEXNET was developed specifically to provide communication services required by Computer Supported Cooperative Work (CSCW) applications but which are not currently available as part of commercially available LAN products. CSCW services include such things as: reliable broadcast communications, dynamic multicasting, and message queuing. Analysis of CSCW networking requirements entailed: reviewing CSCW applications and communications systems; synthesizing a data exchange model for collaborative tools; and defining a target system (PC-LAN). PLEXNET design provides a discussion of: networking tradeoffs, the relationship between PLEXNET and NETBIOS, PLEXNET queue structure, and PLEXNET implementation details. The design and implementation of PLEXNET were validated by performing discrete event simulations comparing response times and resource utilization for three communication paradigms and by developing four collaborative applications which employ PLEXNET for data communications. These applications are: Multi-User LAN Editor, Electronic Discussion System, Contracts Procurement, and Video Switcher.

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