What Is Round Trip Time? Overview, Formula & Usage

Round trip time, or RTT, is a measurement of the milliseconds required for a data packet to head to a destination and for that destination server to send back an acknowledgment of the packet.

What is RTT in networking? 

Think of RTT as a type of timed confirmation receipt. As soon as you send something, the timer starts. It doesn't stop until you get a notification back from the destination server. 

In networking, speed is critical. Most people expect a page to load within three seconds or less. Measuring your RTT ensures that your server responds to requests with the speed and efficacy your audience demands. 

Let's give an RTT example. Your company has an important prospect in Australia, but your server is in Washington. That prospect will need data quickly, but plenty of roadblocks stand in the way, including several routers. 

Your sales team in Australia could measure RTT to ensure the prospect is pleased by the speed before the big pitch happens to close the deal.

How to measure RTT in networking 

You can't call up a server on your phone and ask how quickly things are moving today. Instead, you'll need to use a specialised command. 

The "ping" command from the ICMP Protocol gets its name from sonar technology. Just as boats use sound to measure distance, programmers use pings to measure speed. 

Let's use an example from Windows. To use ping, you will:

  • Press Windows and R.
  • When the Run window opens, type "cmd" and press enter. 
  • Type "ping" and the IP address you'd like to measure. Hit enter.

You'll get a measurement back in that same window, telling you how fast or slow the server is. Test this result against a few other destinations just to see how you measure up.

Can you shorten your RTT?

You've run a few tests, and you realise that your measurement isn't ideal. Your server is responding much slower than the competition. What can you do?

Some RTT roadblocks are out of your control. You could be facing:

  • Too much legitimate traffic. If your LAN is overwhelmed or your server has too many requests, delays are inevitable. 
  • Long distances. The farther away the destination, the longer the journey. 
  • Physical roadblocks. The cables and switches within your network can also impact your speed, and you typically can't change them on the fly. 

But a slow response could also be a symptom of a distributed denial of service (DDoS) attack. These are typically hard to distinguish from normal traffic. But frequent ping testing could help you uncover an attack in progress. When you spot it, reduce your attack surface immediately. Let us explain how to do that.

If you're not under attack but your RTT stats seem slow, consider a content delivery network (CDN). Link together a group of servers that can speed up content delivery. Deploy them on the edge of your network, and consumers can get what they need even faster. 

You can also encourage your regular users to use cached data to make sites load faster. Read our blog post to find out how this approach works. 

References

How Quickly Should a Page Load for Optimal Experience? (July 2020). Search Engine Journal. 

SDN-Assisted Slow HTTP DDoS Attack Defense Method. (April 2018). IEEE Communications Letters.