I have used Ping Plotter always to track any network problems or response times. I wanted more information on how Roundtrip response time is calculated -

When we trace machine say 'F' and assume there are 5 hops to it via Machine A, B, C, D, E then Ping Plotter can throw data like -

Machine from where ping originates 0
Machine A 30
Machine B 40
Machine C 50
Machine D 40
Machine E 60
Machine F 55
Round Trip 50

I would like to know how the Round trip time is calculated as the intermediate machines are taking more time than the round trip time to Machine F.

Waiting for an answer.

Hi.

Each packet goes through each intermediate hop, so the packet going to machine F goes through each of machine A,B,C,D,E on the way to F. Note that the Round Trip always exactly matches the latency at the final destination, because those two datapoints are really just one datapoint - the "Round Trip" just restates the data from the final destination.

There are a few possibilities on why data at hop E might show more latency than hop 5.

* Each data point is a different packet - so the measurement is completely independent of other packets. Network conditions might affect the different packets differently.
* (Similar to previous) Individual data points might show latencies that aren't typical. For best results, you want to look at a number of data points (10 or more, really).
* Each router has its own configuration. This configuration controls how it responds to different kinds of packets. It may be that an intermediate router/machine is down-prioritizing ICMP data, so it takes longer to respond to that packet.
* There are numerous types of packets involved in a traceroute - outgoing packets are ICMP echo requests, but with decrementing TTL. Any router might decide to down-prioritize (or ignore) any type of packet, or a packet with any TTL.
* The return route might be completely different. We can only see the route from your machine to the final destination, but the return route is also a contributor to latency. Any machine/router might pick a different return route, and this return route may be adding different latency. This is most obvious when the final destination (or really, the network that the final destination resides in) sends back via a different route - sometimes this manifests itself in a markedly lower (or higher) latency on the final destination because that router/machine picks a much better (or worse) route to get the data back to you.
* Others - the above lists the ones we see most often, but there are numerous reasons why this could happen.

In all cases, you always need to focus on the final destination. If the final destination is showing reasonable latency and no packet loss, the intermediate hops can show anything they want - it's just an artifact of network configuration. The final destination is the *only* important hop - the other hops are useful only in ways that they contribute goodness (or badness) to the final destination's numbers.

Feel free to follow up with any additional questions about this.

- Pete