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The old design technology also required the use of an extensive database of tariffs. The complexity of the tariff database was probably the main reason behind the need for mainframes. If such a database were incorporated into a desktop minicomputer or a PC-based workstation, users would experience significant processing delays.
Because network topologies do not change with perturbations in any given tariff (they change only with varying design parameters and technologies), using a simplified set of existing or new tariffs is sufficient for designing an optimized network. These topologies can be studied for a detailed cost analysis using one of the many available PC-Line Pricer (PCLP) units. This two-step approach should create a separation between the network design algorithms and the ever-changing tariffs. There should be no need to update the network design package just because a tariff changed slightly.
Some vendors market software packages based on computer simulation for evaluating system performance. LANs (voice or data) and WANs consisting of interconnected data LANs can be evaluated for performance through computer simulation. A good deal of time must be spent on:
Because typical enterprise networks require exorbitant run-times, a simulation tool is no longer an ideal way for synthesizing an optimum network topology. A network topology optimization package based on analytical tools is always the best approach. The resulting topology can be evaluated for studying detailed system response times and availabilities using an expensive simulation tool.
New network design tools are user-friendly, interactive, and can optimize network topology in an iterative fashion while quickly varying the values of critical design parameters. Many of these tools provide special menus for computing end-to-end response times for unusual operational conditions. Some packages even provide special tools for analyzing subsystem security and reliability.
Many new tools based on the graphical user interface (GUI) can evaluate any mix of CPEs, transmission facilities, and network topologies very rapidly in an intuitive manner. Todays design tools also allow the entry of approximate tariffs. But in no way can this new technology eliminate the need for an expert network designer or an architect. Because the expert designer is always involved with what-if type analyses, the potential solutions are meaningful only if the network design tool provides them quickly.
Inputs into this network design package are in the form of flat, sequential files. Results are provided in the form of:
The most important input file, the VHD file, lists the site/node ID, vertical and horizontal coordinates, and total busy hour, time-consistent traffic intensities in bits per second (for data) or millierlangs (for voice) for each location of the enterprise. A from-to data file can also be used to represent exact traffic flows. Another file called the daily traffic profile relates the busy-hour intensities to the other 23 hours of the day for computing the costs on a daily/monthly basis. For an enterprise with many time zones, several busy-hour models can be used.
The second most important input file, the link file, defines the link type that serves each location. Another important input file, the NLT file, defines the link type, capacity, allowed maximum data rate, multiplexing factor, corresponding tariff number, and the multiplying factor for a privately owned facility, if applicable. Up to ten link types and corresponding capacities, allowed maximum data rates, multiplexing factors, corresponding tariff numbers, and multiplying factors can be defined by the NLT file. The tariff file can define up to ten manually entered tariffs, each modeled on 17 parameters. Several link, NLT, and tariff files can be prepared to model many combinations of links and tariffs at all levels of the network hierarchy.
The system design file defines the busy hour, from-to traffic for all significant pairs, if such data is known. Other input files are also used for modeling/designing ACD networks using a mix of virtual facilities and leased FX lines.
The File menu allows the creation and viewing/updating of all input/output files. The Networking menu allows the modeling/design of multilevel voice, data, and IV/D networks using the appropriate star data, directed link, and multidrop data network topologies and voice networks based on star topologies. Network managers can also model, design, and optimize backbone networks in an iterative manner.
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