 automation. Before we appreciate these benefits, let us briefly review the current network capacity planning process. 16.3.1 CURRENT NETWORK CAPACITY PLANNING PROCESS As network traffic increases network capacity needs to be augmented to accommodate the increase in traffic. Network elements typically utilize modular designs; planners have to decide both when Network Measurements new elements are required and when new modules must be added to existing elements. Planners must also decide when link capacity must be augmented; augmenting link capacity may sometimes require augmenting element capacity. At other times link capacity can be augmented by using exist- ing element capacity. Planners start with data on the current network configuration and current network traffic. The data on the current network configuration includes routers, ROADMs, and the links used to connect the various elements as well as element and link capacity that are not currently operational but that are in the process of being added. These data are derived from inventory and configuration manage- ment systems. Planners must also forecast how much traffic a network will be expected to carry. Planners will start with how much traffic a network is currently carrying; this data are derived from performance management systems. Planners then estimate how much growth is expected to occur, this is based on trend analysis of historical data as well as input on new service offers, market conditions and customers. For network capacity planning, a traffic matrix is required, which indicates how much traffic must be carried between different origin-destination pairs. A traffic matrix may be estimated from flow data like NetFlow or JFlow or from an inference method like tomo-gravity [7] that uti- lizes link-interface measurements. Planners then use modeling tools to simulate the impact of the estimated traffic on network capacity and decide where new capacity is needed. An important aspect of simulating the impact of the expected traffic is simulating the 