In steady state, refreshing is performed hop-by-hop, to allow merging.
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When the received state differs from the stored state, the stored state is updated.
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If this update results in modification of state to be forwarded in refresh messages, these refresh messages must be generated and forwarded immediately, so that state changes can be propagated end-to-end without delay.
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Propagation of a change stops when and if it reaches a point where merging causes no resulting state change.
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This minimizes RSVP control traffic due to changes and is essential for scaling to large multicast groups.
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