Table of Contents
Latency
Network latency refers to the time it takes for data to travel from one point to another across a network. Measured in milliseconds (ms), it significantly impacts the performance of applications, particularly those that require real-time responses like online gaming, video conferencing, and VoIP services. Latency can arise from several factors, including physical distance, network congestion, and the performance of routers and switches along the data path.
Latency can be divided into various types. Propagation delay refers to the time it takes for a signal to travel through a physical medium, like a fiber-optic cable. Transmission delay occurs when data takes time to be transferred from a router or switch to its next destination. Processing delay results from the time routers or switches take to inspect and forward the data, while queuing delay is the time spent waiting in a queue to be processed. Queuing delay is often the largest contributor to latency, especially in congested networks, as it can increase unpredictably when traffic spikes occur.
One of the most significant developments related to network latency is the work around reducing queuing delay. RFC 9330 describes theLow Latency, Low Loss, and Scalable Throughput (L4S) architecture, which aims to minimize queuing delay in networks by enabling a network service that can deliver latency of less than 1 ms in ideal conditions. This architecture is designed to coexist with traditional congestion control methods like those used in TCP but uses modern feedback mechanisms to more effectively manage congestion. By applying advanced congestion controls and active queue management techniques, L4S helps reduce bufferbloat, a phenomenon where excess buffering of data in network devices increases latency unpredictably.
Queuing delay, as highlighted in RFC 9330, often becomes a problem when large TCP flows coincide with latency-sensitive applications. Traditional congestion controls like TCP Reno (defined in RFC 5681) tend to create large, sawtooth-shaped delays as the buffers fill up before being drained again. L4S introduces mechanisms that prevent this buildup of queues by marking packets earlier in the transmission process and signaling congestion before the queue becomes too full.
For networks that require strict performance guarantees, particularly in industrial or real-time applications, the concept of deterministic latency is critical. RFC 9055 and RFC 9320 describe deterministic networking (DetNet), a technology that provides bounded latency, ensuring that packets are delivered within a specified time window, regardless of network conditions. This technology is crucial for applications like autonomous driving, industrial control, and augmented reality, where any delay or jitter could lead to catastrophic failures.
Additionally, latency has a direct effect on user experience, especially for interactive applications. As shown in numerous studies, a latency above 50 ms is often noticeable by users and can degrade the quality of experience for web browsing, streaming, and other real-time services. Advanced techniques like those found in RFC 9331 and RFC 9332 work to isolate low-latency traffic from traditional traffic flows, ensuring that latency-sensitive applications maintain consistent performance even during high network loads.
For more technical details and insights on latency reduction methods, see these key resources: - RFC 9330: https://www.rfc-editor.org/info/rfc9330 - Wikipedia on Latency: https://en.wikipedia.org/wiki/Latency_(engineering)
Conclusion
Latency is a critical factor in network performance, particularly for real-time applications that require quick response times. Technologies like L4S, described in RFC 9330, help reduce queuing delay and improve user experience by using smarter congestion controls. With ongoing advancements, including deterministic networking outlined in RFC 9320, efforts are underway to provide ultra-low-latency services across a wide range of applications, ensuring that networks can meet the growing demands of modern-day services and technologies.
- Snippet from Wikipedia: Latency (engineering)
Latency, from a general point of view, is a time delay between the cause and the effect of some physical change in the system being observed. Lag, as it is known in gaming circles, refers to the latency between the input to a simulation and the visual or auditory response, often occurring because of network delay in online games. The original meaning of “latency”, as used widely in psychology, medicine and most other disciplines, derives from “latent”, a word of Latin origin meaning “hidden” . Its different and relatively recent meaning (this topic) of “lateness” or “delay” appears to derive from its superficial similarity to the word “late”, from the old English “laet”.
Latency is physically a consequence of the limited velocity at which any physical interaction can propagate. The magnitude of this velocity is always less than or equal to the speed of light. Therefore, every physical system with any physical separation (distance) between cause and effect will experience some sort of latency, regardless of the nature of the stimulation to which it has been exposed.
The precise definition of latency depends on the system being observed or the nature of the simulation. In communications, the lower limit of latency is determined by the medium being used to transfer information. In reliable two-way communication systems, latency limits the maximum rate at which information can be transmitted, as there is often a limit on the amount of information that is in-flight at any given moment. Perceptible latency has a strong effect on user satisfaction and usability in the field of human–machine interaction.