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4.0.- Advertisement of Link State information |
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| The new link metrics need to be
advertised across the network, so that each router can compute accurate and
consistent QoS routes. One important aspect of such distribution is
its frequency. In general, there is a trade-off between the protocol
overhead of frequent updates and the accuracy of the network state
information available to have a path selection decision. |
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The idea would be to trigger link state advertisement only when
there is significant change in the value of metrics since the last
advertisement. This change can be scaled "absolute" or "relative".
Absolute means partitioning the range of values of a metric in
classes, and triggering an update whenever the metric changes to cross a
class boundary. Relative trigger updates when the percentage change
in the metric exceeds a predefined threshold. Also a periodic trigger
constraint should be added using a hold-down timer to force minimum
spacing between consecutive updates. |
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| The OSPF extensions
described in this document are based on metric updates sent using the
standard, and reliable, OSPF flooding mechanism. |
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