What is RTT (Round Trip Time)?
What is RTT (Round Trip Time)? Why Is It Important For Efficient Pagespeed Performance?
Round trip time (RTT) measures the time, in milliseconds, for data to leave a starting point (scanner) and return to the same point. It is a basic metric used to measure network latency, page load times, and the overall quality of a network.
RTT: The time it takes for a small data packet to travel across the network and return to the same point.
Network latency: Communication delays between a server and a user over a network.
To illustrate with an example, suppose there are two users, one of whom wants to communicate with the other. Let one of them be in Pakistan and the other in America. When making a request in Pakistan, network traffic is transmitted over multiple routers before reaching the server in America. When demand returns to Pakistan, a rough estimate of the time taken for this transmission can be made. This time taken by the forwarded request is called RTT.
Round-trip time is an estimate only. The path between the two locations may change as relay and network congestion can come into play, affecting the overall transmission time.
Why is RTT an Important Indicator of Network Performance and User Experience?
Because RTT only measures data packet transport time, it is a reliable indicator or KPI of pure network performance regardless of application, application server performance, or end-user hardware.
How NetOps Teams Use RTT Data to Provide a Good User Experience
RTT data provides a network-wide latency indicator. NetOps teams often use maximum RTT (or one-way) or average RTT metrics from a given time period to monitor network latency.
Every network monitoring tool can use the RTT (Round Trip Time)value for alerting and reporting.
How is RTT Measured? What Is a Good Round Trip Time?
Round Trip Time (RTT) is typically measured in milliseconds using the Ping command. The ping command is a command line tool that measures the time it takes for a data packet to be sent to a specific destination and come back to its source point.
So what is a good RTT time?
A good round-trip time (RTT) should be under 100 milliseconds for optimum performance.
Why Is It Advantageous to Measure RTT?
The advantages of measuring RTT are as follows:
- It allows users and operators to specify how long it will take for a signal to complete transmission.
- It determines how fast a network can run and its reliability.
What Factors Affect Round Trip Time?
The most important factors affecting the round-trip time; traffic, the physical distance between the user and the servers, the transmission medium and the general infrastructure components.
Now let's go over these factors that most affect RTT in detail:
1. Physical distance
The distance between the user computer (start point) and the server (end point) can cause a high RTT. If the server is located in a different country, the data transfer time will be longer.
2. Response time of source server
It is measured by the Time To First Byte (TTFB) metric, the time it takes for a server to process and respond to a request. If a server is attacked with thousands of concurrent requests (for example, during a DDoS attack), the server's ability to respond efficiently is compromised, resulting in a high RTT.
3. Transmission medium
Connections are made via cables, satellite, wireless or fiber optic. Each path affects connection speed differently.
4. Local area network (LAN) traffic
If a local area is already overloaded, it may affect the connection before it reaches the public internet.
5. Node count and congestion
The connection path may encounter some problems or congestion and may be redirected to intermediate nodes several times. The more nodes touched, the slower the connection and the higher the RTT.
Reducing RTT Using CDN
A CDN is a network of strategically placed servers, each of which maintains a copy of a website's content, and can address factors influencing RTT in the following ways:
1. Points of Presence (PoPs)
A CDN provides a network of geographically dispersed PoPs, each containing cached copies of site content and responsible for communicating with site visitors around them. It reduces the distance a signal has to travel and the number of network hops required to reach a server.
2. Web caching
A CDN caches HTML, media, and even dynamically generated content on a PoP in a user's geographic vicinity. In most cases, a user's request can be handled by a local PoP and does not need to go to a source server, thus reducing RTT.
3. Load distribution
In times of high traffic, CDNs route requests through redundant servers with less network congestion, speeding up server response time and reducing RTT.
4. Scalability
A cloud-running CDN service provides high scalability and the ability to handle an almost unlimited number of user requests. This eliminates the possibility of bottleneck on the server side.
5. Tier 1 access
CDNs have agreements with the largest Internet Service Providers (ISPs) to provide Tier 1 access to the Internet backbone. This reduces the number of network hops a connection must go through and greatly reduces the round trip time of a signal.
Why is RTT Important for Efficient Pagespeed Performance?
One of the factors that has the greatest impact on the performance of a web page is the network's round-trip time, RTT.
The higher the RTT on a resource, the better the performance of using servers that are geographically closer to the user.
Network traffic has two important components:
- Latency
- Bandwidth (Bandwidth)
Latency is the delay time between data sender and receiver, that is, the time it takes from the source sending a data packet to receiving it by the destination.
The delay reason is here:
Propagation delay: The time it takes for a message to reach the receiver from the sender.
Transmission delay: The time it takes to push all the bits of the packet to the link.
Processing delay: The time it takes to process the packet header, check for bitwise errors, and identify its destination.
Queuing delay: The time required for the packet to be processed.
The sum of these delays gives the total delay.
Bandwidth is the maximum throughput of a physical or logical communication path.
