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The emerging international standards for interconnecting computers will be important in IBMs future plans. The Open Systems Interconnection (OSI) protocols are already part of IBMs Systems Application Architecture® (SAA™), implying that they will be implemented across the dissimilar SAA operating systems. Building these complex OSI protocols is costly, and additional expense is involved in verifying conformance and interoperation with other systems. “Porting” a common implementation of these protocols to all SAA systems offers major cost savings, but the difference between systems and the need for high-performance, robust implementations poses problems. The OSI/Communications Subsystem Base solves many of these problems in a general way that may apply to other layered protocols and other systems. The Base provides all necessary operating system services to support the layered communications protocol machines of OSI and allows access to the I/O services of the native operating system as required. This paper discusses the sophisticated communications-oriented environment provided by the OSI/Communications Subsystem Base, which includes multiple threads, back-pressure flow control, resource monitoring, layer modularity, and steps to minimize process switches and data copying. The paper is addressed primarily to systems engineers and communications architects interested in OSI and portability in general.
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