Calculating round trip time
Round Trip Time (RTT) is the measure of how long it takes for a very small packet to travel across the network and for an acknowledgment of that packet to be returned. Consider the typical topology where an Exinda appliance is positioned between the client and the server.
As each packet is intercepted by the Exinda appliance, it is time stamped with a highly accurate nanosecond resolution clock source. Since the Exinda appliance intercepts the packet after the client sends the packet, the start time is not known and so the RTT is determined by summing the round trip time from the appliance to the server and back (Server RTT), and the round trip time from the appliance to the client and back (Client RTT). As more packets are sent from the client through the Exinda appliance make the round trip, the RTT estimate is updated by averaging new information.
The following diagram illustrates how the round trip time is calculated:
This diagram shows how RTT is calculated.
Server RTT:
- RTTs1 = t2 - t1
- RTTs2 = t5 - t4
Client RTT:
- RTTc1 = t3 - t2
- RTTc2 = t7 - t6
Average RTT:
Average Server RTT = (RTTs1 + RTTs2)/2
Average Client RTT = (RTTc1 + RTTc2)/2
Average Total RTT = avRTTs + avRTTc