Methods, systems, and apparatus are disclosed for determining communications latency for transmissions between nodes in a data communications network that include: preparing, by an origin node, to receive an acknowledgement message from a target node, the acknowledgement message indicating that the target node is ready to receive a test message from the origin node; receiving, by the origin node from the target node, the acknowledgement message; sending, by the origin node to the target node in response to receiving the acknowledgement message, the test message; preparing, by the origin node, to receive an echo message from the target node; receiving, by the origin node from the target node, the echo message; and determining, by the origin node, a round-trip communications latency between the origin node and the target node in dependence upon the sending of the test message and the receiving of the echo message.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
 This invention was made with Government support under Contract No. B554331 awarded by the Department of Energy. The Government has certain rights in this invention.