Simulating Your NT Network

In the past, most networks housed few shared resources; users shared access only to file servers, printers, and perhaps a database. Today, many companies distribute information and applications across networks, and many users share access to information. Employees depend on the network to do their job, so when the network goes down, users' loss of access translates into a loss of revenue or customers.

To prevent network outages that cause revenue losses, you need to regularly test your network's capabilities and plan purchases around the network's ability to meet applications' throughput needs. On small networks, you can use network monitoring software and a few simple formulas to diagnose problems or predict the network's reaction to new hardware or software. (For information about testing applications across simple networks, see "Application Testing with Network Monitor," September 1998.) However, as networks grow, their numerous devices and connections make understanding the network impossible. Too many conversations among too many devices via too many network routes occur simultaneously for you to accurately predict how one application's traffic will affect another part of the network. To diagnose problems or test new applications on a complex network, you need to simulate the network--­ use a simulation program, or simulator, to build a software model of key network elements and test how well the model functions with various traffic loads or network designs.

Because the purpose of modeling network traffic is to reduce the number of devices, routes, and transactions on a network to a manageable number, your model must include simplifications and assumptions. The trick to successfully simulating your network is knowing which aspects of the network you can simplify without compromising the model's effectiveness.

To simulate your production network, you need to construct a reasonable representation of the network's topology, including the physical devices and logical parameters that comprise the network. You need to determine how much traffic is on your network during the period you want to emulate. You must specify a question you want the simulation to answer. And finally, you need to run the model through a simulator.

Topology
Your network's topology is the framework for your model. You need to include the following physical devices in your representation of the network: routers, computers, switches, WAN links, LANs, and point-to-point connections. You also need to include network parameters such as router interface settings, LAN speeds, WAN speeds, router capabilities (e.g., backplane speed), routing protocols, and naming conventions. How much detail you need to include depends on the question you want the model to answer. For example, if you are interested in WAN utilization, you don't need to include all your network's PCs in your model; you need to include only the traffic the PCs generate.

You can use software to discover your network's physical devices and logical settings. Some simulators include a discovery tool; others import information about network topology from network monitoring tools. Third-party topology discovery tools include HP's OpenView, Cabletron Systems' SPECTRUM, IBM's NetView for AIX, Digital Equipment's POLYCENTER Manager on NetView for Windows NT, Castle Rock Computing's SNMPc NT, CACI's SIMPROCESS, and Network Analysis Center's WinMIND.

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