What is Latency?

In computer networking, latency is an expression of how much time it takes for a data?packet?to travel from one designated point to another. Ideally, latency will be as close to zero as possible. Network latency can be measured by determining the round-trip time (RTT) for a packet of data to travel to a destination and back again.

High network latency can dramatically increase webpage load times, interrupt video and audio streams, and render an application unusable. Depending on the application, even a relatively small increase in?latency?can ruin UX.

One of the major reasons for poor latency is geography. Highly distributed Internet Protocol (IP) networks traverse vast distances, adding transmission time that can derail an application. In any situation where the latency between sensing and responding needs to be extremely low -- for example, certain actions in autonomous driving -- it makes sense to put the computer that's processing the data as close to the source of the data as possible, a concept known as?edge computing.

Causes of latency in telecom

Latency can be caused by many things, including the following:

·??????Transmission media.?Latency can be affected by the type of media being used to transmit data, voice and video. For example, packets traveling over a?T1?line can be expected to experience lower latency than packets traveling over a?Cat5?cable.

·??????Packet size.?A large packet will take longer to send round trip than a small one.

·??????Packet loss?and?jitter.?Latency can also be introduced by a high percentage of packets that fail to make their destination or too much variation in the time it takes for some packets to travel from one system to another.

·??????Signal strength.?If the signal is weak and has to be boosted by a?repeater, this can introduce latency.

·??????Propagation delays.?If each?gateway?node?has to take time to examine and possibly change the header in a packet -- for example, changing the hop count in the?time-to-live?(TTL) field -- latency will be higher.

·??????Other computer and storage delays.?If a packet is subject to?storage and hard disk access delays?at an intermediate device, such as a?switch, latency is likely to be higher.

Types of latency

Interrupt latency?is the length of time that it takes for a computer to act on a signal that tells the host?operating system?(OS) to stop until it can decide what it should do in response to an event.

Fiber optic?latency?is how long it takes for light to travel a specified distance through a fiber optic cable. For every kilometer (km) covered, a latency of 3.33 microseconds (μs) naturally occurs, according to the speed of light. In reality, however, the per-kilometer latency of fiber optic cables is about 4.9 μs -- this is because light travels slower in a cable. Bends or other imperfections in the cable could make the latency higher.

Internet latency?times are dependent upon distance. The longer a packet has to travel across a global wide area network (WAN), the higher the latency.

WAN latency?can be an important factor in determining internet latency. A WAN that is busy directing other traffic will produce a delay, whether the resource is being requested from a server on the local area network?(LAN), another computer on that network or elsewhere on the internet.

Audio latency?is the delay between sound being created and heard. In sound created in the physical world, this delay is determined by the?speed of sound, which varies slightly depending on the medium the?sound wave?travels through. Sound travels faster in denser mediums: It travels faster through solids, less quickly through liquids and slowest through air. In audio, the acceptable midrange of latency is around 8 to 12 μs. Latencies of 30?milliseconds?(ms) are generally noticed by the listener.

Operational latency?can be defined as the sum time of operations if they are performed in a linear?workflow. In parallel workflows, the latency is determined by the slowest operation performed by a single task worker.

Mechanical latency?is the delay from input into a mechanical system or device to the desired output. This delay is determined by Newtonian physics-based limits of the mechanism (excepting?quantum?mechanics).

Computer and OS latency?is the combined delay between an input or command and the desired output. Contributors to increased computer latency include insufficient data?buffers?and mismatches in data speed between the microprocessor and input/output (I/O) devices.