Técnicas de preprocesado

OPNET is a very powerful network simulation tool [24][25][26]. It has several modules for Application Performance Management, Network Operations, Cell Capacity Planning & Design, and network Research and Development (R&D) studies. These modules can fit different organisations: Enterprise IT, Defense, Service Providers, Network Equipment Manufacturers, Universities, and Research Institutes. OPNET Technologies, Inc. has free research software licenses for the two latter ones, and that is why OPNET Modeler, a commercial package for network modeling and simulation, has been used in my research. It allowed me to design and study communication networks, equipment, protocols, and applications such as UMTS, WiMAX, IPv6, MPLS, and host of others.

A network topology is a combination of nodes and links, and both of them can be user defined in order to study research problems. Simulations can then be performed and the results be analysed for any kind of network element in the simulation network. The OPNET Modeler 14.5 has key features such as scalable and efficient simulation engine, open model source code, different simulation technologies, object-oriented modeling, graphical user interface, integrated debugging and analysis, etc.

Modeler is based on a series of hierarchical editors that can be very efficient, simulating real networks, equipment and protocols. To create node and process models, build packet formats, create filters and parameters, one needs to use the following editors. The most important ones are described below.

Project Editor: The main editor for creating a network simulation is the Project Editor. This is

used to create a network model using models from the standard library, collect statistics about the network, run the simulation and view the results. Using specialized editors accessible from the Project Editor via File> New, one can create node and process models, build packet formats and create filters and parameters. Figure 2-23 showed the project editor in OPNET environment.

Depending on the type of network being modeled, a network model may consist of subnetworks and nodes connected by point-to-point, bus, or radio links. Subnetworks, nodes, and links can be placed within subnetworks, which can then be treated as single objects in the network model. This is useful for separating the network diagram into manageable pieces and provides a quick way of duplicating groups of nodes and links.

Node Editor: The Node Editor is used to create models of nodes. The node models are then used

to create node instances within networks in the Project Editor. Internally, OPNET node models have modular structure. You define a node by connecting various modules with packet streams. The connections between modules allow packets and status information to be exchanged between modules. Each module placed in a node serves a specific purpose, such as generating packets, queuing packets, processing packets, or transmitting and receiving packets. Figure 2-24 showed the node editor in Opnet simulation environment.

Process Model Editor: To create process models which control the underlying functionality of

the models created in the Node Editor, one can use the Process Model Editor. Process models are represented by finite state machines (FSMs) and are created with icons that represent states and lines that represent transitions between states. Operations performed in each state or for a transition are described in embedded C or C++ code blocks. It is used to describe the processes (Protocols, resources, applications, algorithms and queuing policies) that run inside the modules. Figure 23 maps the hierarchical structure among the main models. Figure 2-25 showed the process editor in Opnet simulation environment.

Figure 2-25: Process Editor [35]

There are many more editors in OPNET Modeler [24], such as Path Editor which creates new path objects in order to define a traffic route. Any protocol model that uses logical connections or virtual circuits such as MPLS, ATM, Frame Relay can use paths to route traffic. The Packet Format Editor defines the internal structure of a packet as a set of fields, a packet format contains one or more fields, represented in the editor as coloured rectangular boxed. The size of the box is proportional to the number of bits specified as the field’s size. Link Model Editor creates new types of link objects, each new type of link can have different attribute interfaces and representation, and some important editors for simulating and analysing the results.

Probe Editor: The prob editor is used to specify the statistics to be collected, by using different probes. There are several different types of statistics that can be collected, including global statistics, link statistics, node statistics, attribute statistics, and several types of animation statistics.

While creating a new network model [25], one must first create a new project scenario. The project is a group of related scenarios that explore a different aspect of the network. The scenario

is defined by the topology, the scale and size, and the background scenario for the network. One can use nodes (real-world network objects) and links (communication medium that connects nodes to one another). These take one to the next level: i.e., creating network topologies. It is possible to import the network or manually construct it. There are three different ways of doing it.

 Topology: although the model library that comes with OPNET provides models of various devices used in today’s network, it is possible to import topologies directly from a number of vendor products.

 Rapid configuration: Allows selecting a network configuration, the type of nodes and the types of links.

 Place each individual node from the Object Palette into the workspace.

Once the general network topology is built, we need to add a server. This can be found in the object palette; otherwise we drag a universal server and configure it to our requirements. We then connect the server to the network.

Finally, we add configuration objects to specify the application traffic that will exist in the network. To do this, the Application Configuration and Profile Configuration objects should be dragged into the workspace. How do we configure them?

Communication networks enable applications to exchange data, and each of these applications generates its traffic, [21]. This means, different types of traffic cause and experience a different set of challenges, so we may want to accurately model the traffic patterns generated by a variety of applications. Each application can be enabled or disabled on the client nodes through the use of one or more profiles, and each can be specified as a supported application service type on the server nodes. FTP, E-mail, Remote Login, Video Conferencing, Database, HTTP, Print, Voice and Custom application are the components of the Application Model as shown in Table 2-4. Each of these applications has configurable attributes, such as start time, duration and repeatability.

Table 2-4: UMTS QoS Classes

QoS Class Service Paramter Value Scenario Light Heavy

Conversational VoIP Mean call duration/Hour 120 120 Streaming Streamin g Mean File Volume(kB) Calls/Hour 17500 2 17500 4 Interactive HTTP Mean Page Volume(kB) Calls/Hour 34.4 4 12 34.4 12

Backgroud E-mail Mean File Volume(kB) Calls/Hour 100 4 100 4

In order to configure a workstation to model the behaviour of a user or group of users, one needs to describe their profile. The profile is a set of applications used by that group; on how long and how often applications are used through the day. These profiles can represent different user groups. One can execute profiles at the same time and repeatedly and also configure applications within a profile. Applications can be executed at the same time, one after the other, in fact one has the choice to simulate what really happens in a communication network. We choose which statistics [24] to analyze. Statistics can be collected from individual nodes in the network called object statistics or from the entire network which is called global statistics. One can choose “Individual DES Statistics” to collect single node statistics or one can go to the Probe Editor. The Probe Editor allows one specify the statistics to be collected during simulations, as they can be global statistics, nodes statistics, link statistics, attribute statistics, etc.