Communicating in a network over a path that includes a first node includes: receiving from the first node, at a second node on the path, a packet addressed to a destination; forwarding the packet from the second node to the destination; determining, at the second node, a first time associated with forwarding the packet to the destination; receiving, at the second node, an acknowledgement of the packet from the destination; determining, at the second node, a second time associated with receiving the acknowledgement at the second node; and forwarding the acknowledgment from the second node to the first node. The acknowledgment includes timing information based on the first time and second time.