RSVP must provide correct protocol operation across an arbitrary "cloud" of non-RSVP routers.
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If such a cloud has sufficient capacity, it may still provide acceptable realtime service.
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RSVP automatically tunnels through non-RSVP clouds since routing and reservation functions are independent
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When a Path message traverses a non-RSVP cloud, it carries to the next RSVP-capable node the IP address of the last RSVP-capable router before entering the cloud. This effectively constructs a tunnel through the cloud for Resv messages, which can then be forwarded directly to the next RSVP- capable router on the path(s) back towards the source.
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