Hello Ajay,
I dont think that RSVP would be the right option for this, as RSVP will just reserve bandwidth at the control-plane. At dataplane you would still need to configure Qos policies on the entire path to adhere to the bandwidth reservation.
To avoid packets from getting dropped in the SP domain, you can shape your outgoing traffic to the bandwidth guaranteed by your SP. This will ensure that you donot exceed that bandwidth even when outgoing intf is gig interface.
Then you can create a priority queue for the heartbeat traffic so that this gets priority.
To achieve this effeciently, you might t deploy H-Qos with shaping the class default within the parent policy and then creating a child policy which has the priority and other classes. The H-qos support would deped o the platform that you are using.
Hope this helps.
Regards,
Niranjan
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