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Network planning and design is an iterative process, encompassing topological design, network-synthesis, and network-realization, and is aimed at ensuring that a new network or service meets the needs of the subscriber and operator. The process can be tailored according to each new network or service.

A network planning methodology

A traditional network planning methodology involves four layers of planning, namely:

  • business planning
  • long-term and medium-term network planning
  • short-term network planning
  • operations and maintenance.

Each of these layers incorporate plans for different time horizons, i.e. the business planning layer determines the planning that the operator must perform to ensure that the network will perform as required for its intended life-span. The Operations and Maintenance layer, however, examines how the network will run on a day-to-day basis.

The network planning process begins with the acquisition of external information. This includes:

  • forecasts of how the new network/service will operate;
  • the economic information concerning costs; and
  • the technical details of the network’s capabilities.

It should be borne in mind that planning a new network/service involves implementing the new system across the first four layers of the OSI Reference Model. This means that even before the network planning process begins, choices must be made, involving protocols and transmission technologies.

Once the initial decisions have been made, the network planning process involves three main steps:

  • Topological design: This stage involves determining where to place the components and how to connect them. The (topological) optimization methods that can be used in this stage come from an area of mathematics called Graph Theory. These methods involve determining the costs of transmission and the cost of switching, and thereby determining the optimum connection matrix and location of switches and concentrators.
  • Network-synthesis: This stage involves determining the size of the components used, subject to performance criteria such as the Grade of Service (GoS). The method used is known as "Nonlinear Optimization", and involves determining the topology, required GoS, cost of transmission, etc., and using this information to calculate a routing plan, and the size of the components.
  • Network realization: This stage involves determining how to meet capacity requirements, and ensure reliability within the network. The method used is known as "Multicommodity Flow Optimization", and involves determining all information relating to demand, costs and reliability, and then using this information to calculate an actual physical circuit plan.

These steps are interrelated and are therefore performed interactively, and in parallel with one another. The planning process is highly complex, meaning that at each iteration, an analyst must increase his planning horizons, and in so doing, he must generate plans for the various layers outlined above.

The role of forecasting

During the process of Network Planning and Design, it is necessary to estimate the expected traffic intensity and thus the traffic load that the network must support. If a network of a similar nature already exists, then it may be possible to take traffic measurements of such a network and use that data to calculate the exact traffic load. However, as is more likely in most instances, if there are no similar networks to be found, then the network planner must use telecommunications forecasting methods to estimate the expected traffic intensity.

The forecasting process involves several steps as follows:

  • Definition of problem;
  • Data acquisition;
  • Choice of forecasting method;
  • Analysis/Forecasting;
  • Documentation and analysis of results.

Dimensioning

The purpose of dimensioning a new network/service is to determine the minimum capacity requirements that will still allow the Teletraffic Grade of Service (GoS) requirements to be met. To do this, dimensioning involves planning for peak-hour traffic, i.e. that hour during the day during which traffic intensity is at its peak.

The dimensioning process involves determining the network’s topology, routing plan, traffic matrix, and GoS requirements, and using this information to determine the maximum call handling capacity of the switches, and the maximum number of channels required between the switches.

A dimensioning rule is that the planner must ensure that the traffic load should never approach a load of 100%. To calculate the correct dimensioning to comply with the above rule, the planner must take on-going measurements of the network’s traffic, and continuously maintain and upgrade resources to meet the changing requirements.