aeron-driver/src/main/java/io/aeron/driver/PublicationImage.java
void onRttMeasurement(
        final RttMeasurementFlyweight header,
        @SuppressWarnings("unused") final int transportIndex,
        final InetSocketAddress srcAddress)
    {
        final long nowNs = nanoClock.nanoTime();
        final long rttInNs = nowNs - header.echoTimestampNs() - header.receptionDelta();

        congestionControl.onRttMeasurement(nowNs, rttInNs, srcAddress);
    }
void onRttMeasurement(
        final RttMeasurementFlyweight header,
        @SuppressWarnings("unused") final int transportIndex,
        final InetSocketAddress srcAddress)
    {
        final long nowNs = nanoClock.nanoTime();
        final long rttInNs = nowNs - header.echoTimestampNs() - header.receptionDelta();

        congestionControl.onRttMeasurement(nowNs, rttInNs, srcAddress);
    }
Called from the {@link Receiver} upon receiving an RTT Measurement that is a reply.

@param header         of the measurement message.
@param transportIndex that the RTT Measurement came in on.
@param srcAddress     from the sender requesting the measurement