Each object includes a source instance and a destination instance. The sender generates the source instance for its relationship with the receiver. The value of the source instance is unique for each peer. A given source instance value does not change while the two peers are successfully exchanging hello messages.
The destination instance is simply the source instance value that an RSVP-TE node has most recently received from its peer. If the node has never received a hello message from that peer, then it sets the destination instance value to zero.
Hello adjacency peers monitor the source instance sent by their neighbors. When a peer detects that the value has changed or that its neighbor does not properly report the source instance that the peer transmitted, then the peer treats that neighbor as if it has reset. In these cases, the local peer changes the instance value that it advertises to the neighbor.