Applied Research Laboratory
Publications by Author

Robert Engel


| 1997 | 1996 | | 1995 | request |

Engel, Robert; and Turner, Jonathan S. "Real Time Connection Admission Control with Multistate Traffic Sources," submitted to ICC 1997.

This paper develops a practical method for connection admission control in ATM networks. The method is based on a virtual cell loss probability criterion, is designed to handle heterogeneous traffic types and allows each traffic source to be described by an individual finite-state model with as many states as are needed to describe the source traffic. To make connection admission decisions with respect to individual links, an aggregate finite state model is computed from the individual models and used to estimate the virtual cell loss probabilities. To reduce the computational requirements for maintaining the aggregate traffic model, the aggregate model uses quantized data rates and is maintained incrementally using direct numerical convolution. The approximations required by the quantization process can be done in a strictly conservative way.

Meijler, Theo D.; and Engel, Robert. "Making Design Patterns explicit in FACE, a Framework Adaptive Composition Environment," submitted to Europlop 1996.

Creating applications using object-oriented frameworks is done at a relatively low abstraction level, leaving a large gap with the high abstraction level of a design. This makes the use of a framework difficult, and allows design and realization to diverge. Design patterns are more specific elements of design, and thus reduce this gap. We even bridge this gap by making design patterns and the classes that play a role within them into special purpose software components. System realization becomes a matter of composing special purpose class-components. We also introduce a system, FACE, which supports the visual composition of such specifications.

Huni, Hermann; Johnson, Ralph; and Engel, Robert. "A Framework for Network Protocol Software," submitted to OOPSLA 95.

Writing software to control networks is important and difficult. It must be efficient, reliable, and flexible. Conduits+ is a framework for network software that has been used to implement the signalling system of a multi-protocol ATM access switch. An earlier version was used to implement TCP/IP. It reduces the complexity of network software, makes it easier to extend or modify network protocols, and is sufficiently efficient. Condruits+ shows the power of a componentized object-oriented framework and of common object-oriented design patterns.

Engel, Robert; Bieri, Toni; Keller, Beat. "Signaling in ATM Networks: An Object-Oriented Solution," submitted to IPCCC March 95.

Today the Asynchronous Transfer Mode (ATM) is extensively used on the level of public pilot networks. In the first stages of introduction these networks so not yet support signalling.

However, the standardization bodies ITU-TS (former CCITT) and ATM Forum have already produced first specifications for signalling in ATM networks. These specifications define the basic procedures for point-to-point signalling. Further specifications, that are now being defined, will enlarge the basic set to support fully signalling for multimedia applications between several users (point-to-multipoint).

This signifies that developers of signalling software have to cope with two demands: Until a Recommendation for a specification is approved it undergoes constant change. The introduction of a new specification is associated with an enormous increase in software functionality.

In this paper we show how an object-oriented solution allows the demands of flexibility and extendability to be satisfied. This solution consists of a set of classes that are put together to form a very flexible, extendable framework. This framework can be refined to realize any signalling protocol.

We show how this framework was used to build an implementation of the ATM signalling protocol Q.2931 defined by ITU-TS. The reusability and flexibility of it was verified when the framework classes were integrated in the signalling architecture of a ATM switch.

The framework was realized with object-oriented techniques and implemented in C++.

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Prepared by Vykky Klingenberg Last modified September 18, 1996