Computer Networks (1976)最新文献

This paper presents the agreements (by June 1982) which have been achieved on the international standardization level with respect to the Transport Layer. After defining the architectural environment of Transport Protocols, the functionality of the Transport Layer is described. This results in the identification of groups of Transport Layer functions and protocol classes. By this the specific performance of each protocol class is given. The quality of the service enhancement capability of each protocol class is emphasized. This paper does not present protocol details on formats and mechanisms. The actual status of the agreements between ISO, CCITT and ECMA and the short term expectations are given.

Packet switching has found widespread application in computer communications. Packet radio is the application of packet switching techniques to radio channels. The paper considers packet switching in multiple radio channels with random access. First, a markovian model and an approximate model called “fluid approximation” are formulated and numerical results are presented. Then, the paper demonstrates and analyses an important aspect of the dynamic characteristics of packet radio, namely, the stability considerations. In addition, the stability region is determined.

To the author's knowledge previous studies have been limited to analysis of single radio channels. Besides, the considerations in previous papers have been concentrated only on demonstration if a system is stable or not, while in this paper additionally the stability region is calculated.

Given the current network evolution path, the designer of a data, record, or stored-voice communications store-and-forward system, must generally piggy-back the latter onto an existing bona fide circuit-switched system. This implies relinquishing some ports on the circuit-switched machine to accomodate the store-and-forward system. These ports come at a premium and thus the intermachine link must be optimized in the number of trunks.

The normal design methodologies to obtain the number of trunks are reviewed; an improved approach based on the new concept of the “contrained average” is presented. The constrained average is a methematical construct which derives an appropriate equivalent traffic level L(f,ϵ), with L(f,ϵ) bounded below by the average of the traffic f(t) on an interval [a,b], and above by the maximum of f(t) in [a,b].

The increasing practical importance of data communications, computer networking and distributed data processing has increased the benefits to be gained from a systematic approach to the design, specification, validation, implementation and testing of these kind of systems.

This paper presents an introduction to the State Architecture approach to protocol system specification and also describes an important companion simulation tool.

State Architecture concepts and definitions are presented. Complex protocol systems are built up of interconnections of state-system primitives; specifically, combinational functions, finite-state machines, queues, clocks, delays and derivatives. Aspects of component state and input/output behavior are treated explicitly.

State Architecture Notation (SAN), a formal machine-readable language for specifying protocol systems, is outlined.

The State Architecture Simulator (SAS), a general purpose SAN model simulator is described and example SAS runs on a model of the ADCCP protocol (similar to HDLC and SDLC) are included.

A preliminary evaluation of the State Architecture approach is presented along with a brief comparison to other methods of formal specification.

Numerous modeling approaches exist to formally describe protocols such as: state machines, Petri nets, abstract data types, high level languages, temporal logic. This paper deals with one of them, Petri nets including related models. It presents the most important classes of nets, gives their analysis possibilities and shows how they can be used to model and analyze communication and cooperation protocols.