What is latency?

What is latency? Latency is the time interval between a request and a response. In communications, the lower limit is determined by the means of communication being used. In reliable two-way communication systems, it can limit the maximum rate that information can be transmitted, as there is often a limit on the amount of information that is in transit at any given moment.

In terms of interaction between humans and computers, perceptible latency has a strong effect on user satisfaction and usability, and ultimately productivity. Network latency in a packet-switched network is measured in two forms – one way and round-trip. One-way defines the time from the source sending a packet to the destination receiving it, while round-trip measures the delay time for the packet to reach its destination and back again, thus completing the communication. Round trip latency is more often quoted because it can be measured from a single point.

Probably the most common way of measuring round-trip latency is a service called ping. Ping performs no packet processing at all, it merely sends a response back when it receives a packet. Ping cannot perform accurate measurements, principally because it uses the ICMP protocol that is used only for diagnostic or control purposes, and differs from real communication protocols such as TCP. Furthermore, routers and ISPs might apply different traffic shaping policies to different protocols. However if you think you are suffering from a problem, ping is a good place to start with your troubleshooting.

For further information on how to use ping or how to troubleshoot latency, please browse through the rest of our knowledge base and look at our Network Utilities guide or our Connection Troubleshooting section.