Round trip latency (or Request/Response latency) is the time period between a message being observed at an Agent Point and the message response being observed at the same Agent Point.
This metric records the real latency (as observed at the Visibility Point):
FROM a request to the trading counterparty or venue (e.g. a New Order request or Cancellation request)
TO a response from the trading counterparty or venue (e.g. an acknowledgment or confirmation)
Importantly, these measurements are taken at the Visibility Point - ensuring that it is as close to the trading counterparty or venue as can be obtained.