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The Networking menu also allows the designer to find optimum locations for concentrators/switches by starting with effective solutions and improving these through a fast interactive process. By specifying the design parameters, network managers can model and design data networks based on IBMs SNA, packet-switched networks based on CCITTs X.25 standard, and fast packet-switched networks based on frame relay and ATM technology.
By specifying the design parameters, hybrid voice networks can be modeled using all types of leased and virtual facilities with or without multiplexing. Network managers can also optimize a backbone network topology and model any given topology (for cost and routes).
The Analysis menu allows the designer to model/analyze any point-to-point and several multilink paths for congestion/queuing delays, LAN performance, and reliability. Another Analysis menu item allows the computation of the equivalent monthly cost of hardware and payoff periods for privately owned hardware and transmission facilities. The following section outlines a case study of an EcoNets implementation.
The enterprise in this case study manufactures, distributes, markets, and maintains highly specialized intelligent workstations. It has 17 sites scattered across the U.S., with headquarters in Las Colinas, TX. Two separate networks serve the enterprise. A voice network connects all 17 locations (or PABXs) to a voice switch located at Las Colinas with leased voice-grade lines (VGLs). A separate data network connects workstations located at all of its locations to a host using the SNA-BSC protocol and 9600-bps lines. The newly appointed network manager wants to study the feasibility of a new network architecture, so a consultant is engaged to study the problem.
A database (a subset of the EDB) for network design was created and is outlined in Exhibit 1.
The 17 sites, their vertical and horizontal coordinates, and busy-hour TCA of traffic intensities are shown for both voice (in millierlangs) and data (in bps). Also shown are their names according to a six-symbol city-state (CCCCST) code. Next, an NLT file is defined for these link types. The various design parameters are defined in the SDF. The design parameters for the voice network define the access link type, desired blocking on access lines, trunk line type, and desired blocking on trunks. The major design parameters for the data network are ATP (analysis type is equal to 3 for response time modeling for an SNA-BSC network), user port rate, host port rate, nodal processing time in ms for each transaction, and half-modem time in ms spent in going through the modem in one direction.
The consultant first modeled the existing voice and data networks. The monthly costs for these two separate networks were $60,930 and $10,017, respectively. The EcoNets tool was then used to study various topologies consisting of switches and three link types for voice and only the 9600-bps line for data (higher-speed lines resulted in no improvements). The results are shown in Exhibit 2. The optimum voice network topology (see Exhibit 3) consisted of two switches (as determined by the EcoNets center-of-gravity finding item on the Networking menu) and 56K-bps lines, each of which carries eight digitally encoded voice conversations.
The one-time cost of 17 special hardware boxes that perform voice encoding and multiplexing in the same box did not influence the optimum network topology. The optimum data network topology (see Exhibit 4) consisted of the same two switches as was used for the voice network and 9600-bps lines. The costs of these optimum networks were $37,546 and $9147, respectively. This represented a monthly savings of $23,254 (or about 32.8% of existing costs). No matter how the figure is examined, it amounts to a substantial savings.
Exhibit 1. Enterprise Database (EDB) for a 17-node Network Design (voice/data applications)
Exhibit 1. (Continued) Enterprise Database (EDB) for a 17-node Network Design (voice/data applications)
Exhibit 2. Costs vs. Number of Switches and Link Types.
Additional savings can be achieved by computing the total data rate (in bps) of voice conversations from each site and adding the regular data traffic and constructing a new VHD file. An optimum star-data topology consisting of two switches and 56K-bps lines can be achieved. The topology is identical to that of the optimum voice network (see Exhibit 3) and the monthly cost is about the same. The cost of the separate data network disappears completely. The new monthly savings of $33,392 represent 47.1% of existing costs. These additional savings resulted from the fact that the 56K-bps line used in the integrated voice/data network had enough excess capacity to handle the data traffic. Such a phenomenon is similar to the one experienced by network managers working with larger T1 networks in the 1980s. Those networks had enough excess capacities in the T1 trunks to handle the data traffic. The broadband data networks of the future should have enough excess capacity to handle voice traffic.
Exhibit 3. Optimum Star Data Network Topology for IVD Application.
Exhibit 4. Optimum MD-Data Network Topology with Two Switches.
This example illustrates only a small enterprise network. Bigger savings can be achieved through optimization of larger enterprise networks. Savings result because: integrated networks make use of excess capacity, and aggregation of many separate applications allows the deployment of transmission facilities with higher capacities that generally cost less on a per-transaction basis. These type of network planning and design tools provide network managers with many more opportunities for providing a cost-effective, integrated network to the enterprise.
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