 weeks. Even if the forecast is off, there are no stranded static end-to-end IP links but rather with endpoints (tails) and possibly spare regenerators. The penalty is low since each tail can be repointed to a different direction as needed and the spare regenerators are pooled resources and can be used elsewhere. The remainder of this section defines some of the key measurements needed for network capacity planning in the SDN environment. 16.3.3 TRAFFIC MATRIX DATA Deriving the traffic matrix data required for network planning can be challenging. One option is to use a flow measurement product such as NetFlow [8] or JFlow. These products offer multiple options for collecting data on network traffic with different levels of granularity. Traffic is often collected for each 5-tuple, that is, source IP address, destination IP address, protocol, source port, and destination port. Because of the volume, data sampling is often used. Flow measurements may only be collected on selected router interfaces either because some elements do not support the collection of flow measurements, or to reduce the volume of the data generated. For network capacity planning the origin and destination routers where the traffic enters and exits the network is required. It may be necessary to infer the origin and destination routers from the origin and destination IP addresses, which requires extracting routing tables from the routers and doing rout- ing table lookups. An alternative approach to derive a traffic matrix, for example, if flow measure- ments are not available or incomplete, is to use an inference method like tomo-gravity. Inference methods do not generate the actual traffic matrix but the results are often adequate for modeling. Such methods use mathematical techniques to derive traffic matrices from link interface measure- ments, which are easier to collect; if incomplete flow measurements are available they could be used to improve the quality of the resulting traffic matrices. The new SDN capabilities coupled with new oppor