What is round trip time (RTT)?

Round trip time (RTT) is a measure of the latency of a network, particularly in milliseconds. It is the time between initiating a network request and receiving a response. The higher latency times adversely affect the bandwidth and the end-user experiences in interactive applications e.g. web browsing.

It’s a significant metric for measuring the efficiency of a connection on a LAN or a larger network. It is usually used by the network administrators to determine the reliability and speed of network connections.

A CDN is primarily focused on reducing the round trip time of network connections. The latency times can be reduced by reducing the RTT and by eliminating those points where round trips are needed by carrying out necessary modifications in SSL/TLS handshake.

We can estimate the round trip time of a connection by using ping utility which is by default available on all computers. The following is a good example of using the ping utility to test it.

round trip time

Common factors affecting round trip time

  • Infrastructure components
  • Network traffic
  • The physical distance along the path between a source and a destination.

List of factors

  • The nature of the transmission medium – The composition of transmission affects the speed of connection or how fast it can move. Any connection made over optical fiber will behave way more different than the connections built on copper.

  • Local area network (LAN) traffic – The amount of traffic present on any Local Area Network also plays a very crucial role in determining the round trip time because in some cases the heavy traffic in a LAN makes it very difficult for a connection to reach a larger network. For example, if many users are using browsing their board or exam results simultaneously, it may impact the RTT even though the larger network is working normally and has the capacity to host more connections.
  • Server response time – The server response time also plays a huge role in network latency. When a server has too many requests to entertain, such as in a DDoS attack, its ability and capacity to respond to requests cause a delay.

  • Node count and congestion – The round trip time is also greatly affected by the patch taken by the connection. If a connection has to go through a patch which is made up of numerous intermediate nodes then it has to hop through all those nodes thereby increasing its time to reach to the network. As a rule of thumb, the greater the number of nodes a connection touches the slower it will be. Other reasons might be a node experiencing congestion due to other’s network traffic.

  • Physical distance – The physical distance also plays a significant role. However, we can move the content closer to a user by using CDNs thereby optimizing the physical distance.

How can a Multi CDN improve round trip time?

A CDN can reduce round trip time by maintaining the servers inside the IXPs and optimizes network paths between locations for end-users to access the content. Since different CDN providers perform differently in different regions around the world, a catered approach for each region is recommended. 

Multi CDN can reduce it drastically by deploying different best-performing CDNs for different regions.


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