edVirtus Reference

What Is Latency?

What Causes Latency in Communication Networks?

Latency is the time required for information to travel from its source to its destination through a communication system. It is typically measured in milliseconds (ms) and represents one of the most important performance parameters of modern communication networks. Low latency is essential for applications such as voice communications, online gaming, industrial automation, and remote control, while higher latency is generally acceptable for activities such as email and file transfers.

Latency is not caused by a single process but is the sum of several different delays occurring throughout the communication system. These include processing delay, while equipment examines and forwards packets; queuing delay, when packets wait in buffers during periods of congestion; transmission delay, while the bits are placed onto the communication medium; and propagation delay, the time required for the signal itself to travel through the transmission medium.

A useful analogy is sending a parcel through a postal service. The total delivery time includes preparing the parcel, waiting for collection, transporting it between sorting centers, and finally delivering it to the recipient. Similarly, network latency is the combined result of several stages rather than simply the travel time of the signal.

The physical transmission medium has a significant influence on latency. Electrical signals in copper cables and light pulses in optical fibers travel at approximately two-thirds the speed of light in free space, while radio waves propagate through the atmosphere at nearly the speed of light. For long-distance communication, the propagation delay alone can become significant. For example, a signal travelling to a geostationary satellite experiences a one-way propagation delay of approximately 120 ms, producing a round-trip delay of around 240–280 ms once equipment processing is included.

Different applications have different latency requirements. Web browsing and email are relatively tolerant of delay, whereas Voice over IP (VoIP), video conferencing, and interactive gaming require much lower latency to provide a satisfactory user experience. Industrial control systems, autonomous vehicles, and remote surgery demand extremely low and predictable latency because excessive delay may compromise safe operation.

Modern communication networks employ several techniques to reduce latency. These include high-speed switching, efficient routing, Quality of Service (QoS), edge computing, and faster transmission technologies such as optical fiber and 5G. Reducing unnecessary packet processing and minimizing network congestion also contribute to lower latency.

It is important to distinguish latency from jitter. Latency measures the average time taken for information to travel through the network, whereas jitter measures the variation in that delay between successive packets. A network may exhibit relatively high latency but very little jitter, or vice versa. Both parameters influence communication quality but affect different types of applications.

Today, latency is one of the principal measures used to evaluate communication networks. It influences the performance of cloud computing, online gaming, video conferencing, satellite communications, mobile networks, and industrial automation. As communication systems increasingly support real-time and mission-critical applications, minimizing latency has become one of the key objectives of modern network design.