Wondering what’s round trip time and what’s its impact on performance? This article will cover everything you need to know about the round trip time (RTT), how it’s calculated, what affects it the most, and how a CDN can help to decrease it. 

What’s Round Trip Time?

Round trip time (RTT) measures the time it takes for the data to leave a starting point (the browser) and return to that very same point in milliseconds. It is a key metric used to measure network latency, page loading times, and the overall quality of a network.

RTT (browser – server – browser) – Source: RocketCDN

How To Calculate Round Trip Time (RTT)

Round trip time is the average server round-trip time plus the average round trip to the final client. 

When a user requests page content on Chrome, a request is sent to the server to load that page. This request/response scheme takes time, and those “lags” are called “propagation delays”. Two propagation delays constitute one round trip time.

RTT calculation and propagation delay explained – Source: RocketCDN

When it comes to the actual calculation, there is one simple formula to remember.

RTT formula- Source: RocketCDN

How to Fix an RTT Average

If you want to fix an RTT average, you should aim at improving the propagation delay time on both the browser and server sides. 

To calculate the total RTT average, it’s crucial to know your client’s average server RTT and Average Client RTT. 

Let’s break down the process into two simple steps.

Step 1: the calculation needs to be done on the server and client sides: 

Step 2: then you have all the data to calculate the average total RTT

Average Total RTT = avRTTs + avRTTc

What’s a Good Round Trip Time?

A good round trip time (RTT) should be below 100 milliseconds for optimal performance. Anything above may affect the connection depending on the application. 

Example of a Round Trip Time at Microsoft 

Microsoft has guidelines and rules to maintain healthy network quality. They published their network Performance requirements from a Skype for Business client to Microsoft network Edge. Here are the performance target requirements for optimal Skype for Business media quality.

RTT goal – Source: Microsoft

How to Check My Round Trip Time – Example

Round trip time can be seen thanks to a “ping” via the terminal command of your computer. Follow the steps below to launch the command line: 

The round-trip times (RTTs) are expressed in ms from the third to the fifth column:

Measuring RTT with the terminal window – Source: RocketCDN
Measuring RTT with the terminal window – Source: RocketCDN

How Does Round Trip Time Work?

Round trip time is based on two main parameters:

What Affects Round Trip Time?

The common factors affecting Round trip time are traffic, physical distance from the user to the servers, the transmission medium, and the overall infrastructure components.

Let’s go over each factor that impacts RTT the most:

  1. Physical distance – the high distance between the user computer (starting point) and the server (ending point) can be responsible for a high RTT. The data transfer time will take longer if the server is located on the opposite side of the world. 
  1. Response time of the origin server – measured with the Time to First Byte (TTFB) metric, it’s the amount of time it takes a server to process and respond to a request. If a server is attacked with thousands of simultaneous requests (e.g, during a DDoS attack), its ability to respond efficiently will be compromised, resulting in a high RTT.
  1. Transmission medium – Connections are made via cables, satellite, wireless or optical fiber. Each way affects the connection speed differently.
  1. Local area network (LAN) traffic – if a local area is already overloaded, it can impact the connection before it reaches the public internet. 
  1. Node count and congestion – the connection route may encounter some issues or congestion and may be redirected several times to intermediate nodes. The more nodes are touched, the slower the connection will result in a high RTT.

What’s the Impact of RTT on Performance and How a CDN Can Help

If the RTT is too high, time-outs and performance issues are very likely to occur. The Core Web Vitals of your website will also be impacted, resulting in a poor user experience. 

Let’s take the example of the Largest Contentful Paint (LCP), which measures when the page starts loading the largest text block or image rendered on the screen. To ensure that the resource starts downloading as soon as possible, you should reduce the distance from the browser to the server. 

This is exactly the purpose of a CDN: making the content available closer to visitors.

Let’s have a closer look at the four main reasons why a CDN can help reduce the RTT and improve performance:

Reducing physical distance with a CDN – Source: RocketCDN
Pro-tip for advanced caching: In addition to a CDN, you can also use WP Rocket, one of the best cache plugins for WordPress.

Scenario #1 – Performance results – No CDN 

Scenario #2 – Performance results – With a CDN 

Using RocketCDN to Reduce RTT 

RocketCDN is a powerful CDN that uses caching and more than 35 Points of Presence to distribute the data around the globe, ensuring your website a low RTT.  It’s also very simple and easy to use – RocketCDN does all the advanced settings for you. 

Sounds promising? 

Let’s go over the best features of RocketCDN that will help boost your performance and keep your RTT below 100 ms. 

✅  RocketCDN: maintain a low RTT and TTFB but a high uptime 

Present in more than 35 markets and on four continents, RocketCDN is a powerful CDN that helps reduce RTT and TTFB. The CDN ensures fast responsiveness for all international visitors located around the globe. Nobody wants any latency to occur, and a fast website is the key to a great user experience. 

Shorter RTT and lower TTFB with RocketCDN – Source: RocketCDN

✅ Decrease the server response time with powerful caching

RocketCDN uses caching to make the content available faster for international users via PoPs, resulting in a faster server response time and increased performance. 

RocketCDN distributes content to make it available faster for international users via Pops – Source: RocketCDN

  Network security and DDoS attacks protection

RocketCDN includes Secure Sockets Layer (SSL) traffic and protects your origin server in case of DDoS attacks. If your website is targeted, RocketCDN will ensure that it doesn’t reach the origin server. Visitors won’t experience any downtime. They will simply be redirected to the other edge servers. And most importantly, the RTT will not be impacted!

✅ Straightforward installation and compatibility with any website technology

RocketCDN works with any website technology making it easy to connect to any CMS, including WordPress or Joomla. There is a WordPress plugin that automatically points your assets to RocketCDN.

Dedicated WordPress plugin – Source: WordPress repository

✅  Unlimited bandwidth and high scalability 

RocketCDN can easily handle many visitors and unexpected traffic peaks with unlimited bandwidth. This is great for reducing the round trip time and avoiding any “hops” in the connection.

✅  A Cache Hit Ratio > 90% 

With a Cache Hit Ratio superior to 90%, it’s safe to say that the data is properly cached and that RocketCDN can process many requests successfully. Like RTT, Cache Hit Ratio is also an important performance metric for a CDN.    

Managing your Round trip time is straightforward with RocketCDN! 

Using RocketCDN allows you to distribute content more efficiently worldwide, save on RTT, TTFB and increase the performance of your website. RocketCDN does all the heavy lifting for you – you don’t need to worry about the technical settings! On top of that, you have up to 48 hours to cancel it if you don’t see any improvements. Try RocketCDN and start reducing your round-trip time today!