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3.0.- Metrics  

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The process of selecting a new path requires:
  1. Knowledge of the flow requeriments and characteristics.
  2. Information about availability of resources in networks.
  3. Evaluate the amount of resources that has to be allocated to support the new flow. This, because it can be decided not to accept a new flow, even when resources are available, if the cost of the path is deemed too high.

  

The metrics involve in the path selection process are:
  1. Link available bandwidth
      The relevant metric to accept a new flow is the current amount of available (i.e., unallocated) bandwidth. Changes in this metric need to be advertised as part of one extended LSA, so that accurate information is available to the path selection algorithm.
         		  
  2. Link propagation delay
      To be able to identify high latency links, i.e., satellite links, which may be unsuitable for the request. This information has to be flooded as part of one extended LSA with the advantage that the timely disimination is not critical, since this parameter is unlike to change significantly over time.
         		  
  3. Hop count
      Smaller number of hops is preferable because it consumes fewer network resources; then the selection algorithm will attempt to find the minimum hop path capable of satisfying the given request. Fortunately, this is a metric that does not affect LSAs because it is used already implicitly as part of the path selection algorithm.