A comprehensive network management function built into the interconnection network provides a means of meeting user needs of fault tolerance, performance, accounting, and security. However, meeting these needs on a heterogeneous interconnection network is several levels more complex than on a homogeneous network because of the existence of multiple protocol stacks for communication. An architecture that will solve this problem by analyzing the heterogeneous interconnection network as a single entity is proposed. The authors present the design issues evaluated in choosing this approach and establish the need for the various components in this architecture. An overview is presented of each of the components, and their place in the architecture is pointed out.>

Broad-band technology provides several advantages for personal computer local area networks (PC LAN's) including mature readily available transmission technology, large total bandwidth, support for multiple services, and cost-effective expansion from very small to very large systems. This paper presents an overview of basic broad-band technology, hardware, software, and protocols needed for PC LAN's. Gateways and network management are also considered. Recent PC LAN products are compared, with a more detailed case study of the PC LAN developed by IBM and Sytek.

Interconnection of multiple broadband local area networks to form an integrated packet transport system presents several challenges. To take full advantage of broadband systems, assignment of nodes to channels must be dynamic, leading to the use of a flat address space. Combined with the desire to avoid reliance on a central server or complex routing in packet forwarders, this addressing scheme leads to adoption of a controlled flooding technique to “discover” the best path to a destination node. This discovery procedure sets up a path through internetwork forwarders for use by subsequent packets to the same destination. This paper describes the design and implementation of such a technique in Sytek's LocalNet(TM) systems along with several refinements which increase performance and keep the worst case load for route discovery below a few percent of network capacity.

It is becoming increasingly important that communication protocols be formally specified and verified. This paper describes a particular approach–the state transition model–using a collection of mechanically supported specification and verification tools incorporated in a running system called AFFIRM. Although developed for the specification of abstract data types and the verification of their properties, the formalism embodied in AFFIRM can also express the concepts underlying state transition machines. Such models easily express most of the events occurring in protocol systems, including those of the users, their agent processes, and the communication channels. The paper reviews the basic concepts of state transition models and the AFFIRM formalism and methodology and describes their union. A detailed example, the alternating bit protocol, illustrates varous properties of interest for specification and verification. Other examples explored using this formalism are briefly described and the accumulated experience is discussed.

A new approach to situation assessment is an automated distributed sensor network (DSN) consisting of many "intelligent" sensor devices that can pool their knowledge to achieve an accurate overall assessment of a situation. Laboratory experiments were conducted to investigate potential DSN organizations and to ascertain some general design principles. These experiments have been performed with a network of "sensor nodes," each of whom sees only a small portion of the entire environment and attempts to identify the environmental mobile entities as quickly as possible. To do this, they must cooperatively communicate their hypotheses and data, using a limited number of messages. Two general DSN organizations were tested. The first was hierarchical. The second was an "anarchic committee" whose nodes could each send messages to one, some, or all other nodes. The performance of the committee organization consistently surpassed the hierarchical one. This lent support to the contention that DSN architectures need to emphasize cooperative aspects of problem-solving. A machine-based simulation of such a network that achieved performance levels comparable to that of the human committee DSN organization was also constructed and tested. Because most situation assessment communications concern hypothesis updating and revision, minimizing communication requirements through the concept of active "hypothesis processes," which are responsible for predicting their own evolution over time, is suggested.

While early protocol design efforts had to rely largely on seat-of-the-pants methods, a variety of more rigorous techniques have been developed recently. This paper surveys the formal methods being applied to the problems of protocol specification, verification, and implementation. In the specification area, both the service that a protocol layer provides to its users and the internal operations of the entities that compose the layer must be defined. Verification then consists of a demonstration that the layer will meet its service specification and that each of the components is correctly implemented. Formal methods for accomplishing these tasks are discussed, including state transition models, program verification, symbolic execution, and design rules.

CCITT has proposed Recommendation X.75 as a technique for interconnecting public data networks in a standard way. However, this is not the only or necessarily the best approach. This paper focuses on two major factors in determining the merits of different network interconnection approaches, and compares the X.75 approach to a few alternatives in each of these areas.

Reliable and efficient communication in computer networks requires specialized communication protocols. Previous research has emphasized system performance at lower levels, within the communication network itself, while this work considers the efficiency of protocols for communication between processes in the host computers attached to a computer network. Throughput and delay are chosen as the primary performance measures. Network transmission characteristics, protocol parameters, and process behavior all interact in determining the efficiency of communication between remote processes. Models are developed to determine the impact of protocol parameters such as retransmission interval, window size, buffer allocation, packet size, and acknowledgment strategy on protocol performance. Several graphs showing quantitative performance results for representative situations are included.