2.6 Confirmation

To request a confirmation for its reservation request, a receiver Rj includes in the Resv message a confirmation-request object containing Rj's IP address. At each merge point, only the largest flowspec and any accompanying confirmation-request object is forwarded upstream. If the reservation request from Rj is equal to or smaller than the reservation in place on a node, its Resv is not forwarded further, and if the Resv included a confirmation- request object, a ResvConf message is sent back to Rj. If the confirmation request is forwarded, it is forwarded immediately, and no more than once for each request.

This confirmation mechanism has the following consequences:

• A new reservation request with a flowspec larger than any in place for a session will normally result in either a ResvErr or a ResvConf message back to the receiver from each sender. In this case, the ResvConf message will be an end-to-end confirmation.

• The receipt of a ResvConf gives no guarantees. Assume the first two reservation requests from receivers R1 and R2 arrive at the node where they are merged. R2, whose reservation was the second to arrive at that node, may receive a ResvConf from that node while R1's request has not yet propagated all the way to a matching sender and may still fail. Thus, R2 may receive a ResvConf although there is no end-to-end reservation in place; furthermore, R2 may receive a ResvConf followed by a ResvErr.