Peter Lorenz German smaller fonts Simulation und Animation

4. GPSS/H Queueing Models

GPSS is often wrongly classified as a simulator for queueing systems. That's a mistake: recent GPSS-implementations, especially GPSS/H, are universal simulation systems, suitable for simulating any model in discrete, event-oriented simulation.
What is true is that GPSS had originally been designed as a simulator for queueing systems and even today it is still very suitable for this purpose.
That might be the reason for beginning the introduction to GPSS with examples of queueing models. In the following chapter 4 we will, with the help of these examples, discuss the original, easy to describe classes of entities and language elements. In chapter 5 we will have to proof that GPSS/H is a truly universal simulation language, whose usage today extends the original one by far.


4.1. Transactions and Facilities

Transactions (short Xacts) and Facilities are components needed for the simplest queueing system, the single server or single channel queueing system. Here, Transactions are used for mapping demands or requests and a Facility for mapping the service station. This introductory example will finally be supplied with statements necessary for its animation.

4.2. Blocks, Control Statements and Compiler Directives

GPSS/H language elements can be divided into these three classes. The paragraph describes the basic features of these language components and their interaction.

4.3. Queues and Storages

The transition from a single server to multi-channel queueing systems will be combined with an introduction to the following classes of model elements: Queue and Storage.

4.4. Logic Switches and Branches

A queueing system contains several service stations, requested by demands. For its reconstruction it is necessary to be able to split and gather streams of requests or demands, the so-called Transactions in GPSS. By using Logic Switches and the Blocks TRANSFER, GATE and TEST the programmer can meet these requirements.

4.5. Attributes of Transactions

In contrast to the classic theory of queueing systems, there are hardly any applications using homogeneous request streams, which consist of equal elements. Transactions can be assigned with attributes or Parameters carrying different values and thus allow modeling their different behavior. Additional attributes are their Priority and their Mark Time word.

4.6. Searching, Counting and Classifying

Attributes of Transactions can be used for counting and searching. They also serve as individual cycle counter. Tables can be used for classifying of values.

4. GPSS/H Queueing Models
4.1.Transactions and Facilities
4.2.Blocks, Control Statements and Compiler Commands
4.3.Queues and Storages
4.4.Logic Switches and Branches
4.5.Transaction Attributes
4.6.Searching, Counting and Classifying
Global Outline
1.Introduction to Modeling, Simulation and Animation.
2.Proof Animation™.
3.GPSS/H as a Programming language.
4.GPSS/H Queueing Models.
5.GPSS/H Controling Concepts.
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