Node Domain

Network models in OPNET are constructed from two broad classes of components: communication nodes and communication links. The internal structure of these objects, for the most part, is not visible at the network level. This chapter presents the methods used to specify the internal structure and therefore much of the capabilities of communication nodes. For a discussion of communication links, refer to the Communication Mechanisms chapter in this manual. Both the structural complexity of network nodes and their scope of activity can vary greatly depending on the system which is modeled. On the low end of complexity and function, simple terminals (connected to a host computer via serial connections) can be considered nodes of a star network. On the other end of the complexity spectrum, the network management center of a nationwide public packet network can also be considered as a single " hub " node. The table below presents some typical examples of node models that can be built with OPNET. Since the goal of using OPNET is to construct executable simulation models of communication networks, internal node functions must be modeled sufficiently well that the overall simulation of network behavior is accurate. The system provided by OPNET is powerful enough to specify virtually any form of communication node. Moreover, it supports reusability of node substructures, and sharing of effort between various members of a design or development team. OPNET's node modeling system is based on a block-structured approach, which is familiar to most engineers and used extensively in modeling system architectures. Some examples of other applications which use this approach are signal processing, process control, and three-dimensional computer graphics. In these applications, the blocks operate respectively on analog or digital signals, fluids or other media, and polygons or vectors. Block-structuring is a natural technique for describing hardware systems, and can also be an effective tool when Typical Node Models Node Type General Functions Workstation Can generate and receive transfers of files or sparse packets and manage several concurrent network connections. Packet Switch Supports large numbers of incoming and outgoing data links and performs packet routing at high speeds. Satellite Terminal Generates and receives packets according to a channel access protocol. Acts as a multiplexor for many incoming links. Remote Data Sensor Acts as a simple source of packets, usually transmitting them in bursts.