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Wireless Networking Handbook
(Publisher: Macmillan Computer Publishing)
Author(s): Jim Geier
ISBN: 156205631x
Publication Date: 09/01/96

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Verifying the Design Through Physical Prototyping

Construction and testing of the part of the system you want to verify is known as physical prototyping. It uses the actual hardware and software you might eventually deploy. In some cases, you could include the prototype as part of the initial implementation, perhaps as a system pilot. The prototyping can also take place in a laboratory setting or testbed.

The following are the main attributes of physical prototyping:

  Yields very accurate (real) results because you are using the actual hardware and software
  Is relatively inexpensive because you can obtain components under evaluation from vendors
  Takes time to reconfigure
  Requires access to network components, which can be a problem if you do not have easy access to vendors (from remote areas, for example, such as ships at sea, the South Pole, and so forth)
  Requires space to layout the hardware

Typically, you do not need to physically prototype the entire system, especially those parts that other organizations have implemented without encountering problems. Consider prototyping any solutions that have not been tested before. The following are some examples:

  Interfaces between wireless users and network resources located on a wireline network
  Access from users to mainframe applications
  Operation of newly developed applications
  Operation of the system in areas where there is a high potential for inward and outward interference

Verifying the Design through Simulation

Simulation is software that artificially represents the network’s hardware, software, traffic flows, and utilization as a software model. A simulation model consists of a software program written in a simulation language. You can run the simulations and check results quickly, greatly compressing time by representing days of network activity in minutes of simulation runtime.

The following are the main attributes of using simulation for verifying the design:

  Results are only as accurate as the model. In many cases you need to estimate traffic flows and utilization.
  After building the initial model, you can easily make changes and rerun tests.
  A simulation does not require access to network hardware and software.
  A simulation does not require much geographical space, just the space for the hardware running the simulation software.
  Simulation software is fairly expensive, making simulation economically unfeasible for most one-time designs.
  The people working with the simulation program will probably need training.

For most implementations, you do not need to run simulations. Consider using simulation for the following situations:

  When needing a better understanding of the bandwidth requirements (system sizing) based on predicted user activity. (It is not practical to do this with physical prototyping.)
  If you are in an area where it is difficult to obtain hardware and software for testing purposes.

There are simulation tools on the market that can assist designers in developing a simulation model. Most simulation tools represent the network using a combination of processing elements, transfer devices, and storage devices.

Mil 3’s Opnet

Mil 3’s Opnet simulator has evolved as a response to the problems resulting from network complexity. Structured around a top-down, graphical hierarchy of representation that uses the latest software technology, nodes are represented as objects that communicate through data-flow networks and can be quickly customized to specific details. The entire system, including statistical analysis of network traffic, is portrayed through an X Window graphical user interface. As a result, the designer can think in terms of basic architectures and explore the consequences without coding a design from the bottom up.

Opnet is structured as a series of hierarchical graphical editors that address each level of network design. Consisting of three levels, the highest tier is based on connectivity, operating as a schematic-capture function. Graphical representations of a network can be superimposed on backgrounds representing floor plans or geographic areas. The second level, the node editor, captures node activity in terms of data-flow analysis of hardware and software subsystems. The third level contains a process editor that defines the control flow, such as a protocol or algorithm.


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