Propagation delay refers to the time it takes for a signal to reach its intended destination. It is related to networking, electronics, and physics.

Answering the question “What is propagation delay?” means responding to it in relation to at least three fields.

In a computer network, propagation delay is the interval between sending a signal and receiving it. In electronics, meanwhile, it is the time it takes for an input to gain stability then change to the point for the output to become stable and ready for change. Finally, in physics, it is the amount of time for a signal to travel to its destination.

Other interesting terms…

Propagation delay is related to several terms, some of which are described in more detail below.

### What Concepts Are Related to Propagation Delay?

The following terms are connected to propagation delay:

• Contamination delay: In digital circuits, this refers to the minimum amount of time from when an input changes until the output starts changing value. Unlike in propagation delay where the input reaches stability, the change doesn’t cause the output to become stable in contamination delay. The change in value goes only halfway.
• Latency: This is the amount of time that passes between a cause and an effect when you expect a physical change to occur on a system. In gaming, it is known as “lag,” which is the latency between an input to a simulation and a visual or auditory response. It often happens due to a network delay when you’re playing an online game.
• Time of flight: This refers to the time it takes for an object, particle, or wave (acoustic, electromagnetic, etc.) to travel through a medium.

### How Does Propagation Delay Work?

Let us look at how propagation delay works on a clock using the diagram below.

In the diagram of a clock below, a flip-flop is a latch or circuit that has two stable states that can be used to store state information. The logic serves to control when to send the signal to the next flip-flop and routing simply refers to the wires that connect the two flip-flops.

All that said, the farther the two flip-flops are from one another, the longer the propagation delay. Also, the more logic that needs to be applied, the longer the propagation delay. Finally, the longer the routing (or wire) is between the two flip-flops, the longer the propagation delay. The longer the propagation delay, the slower the clock runs.

Think of it this way, flip-flop 1 is the second hand on a clock. The second hand needs to run for 60 seconds before flip-flop 2 (the minute hand) can change to indicate that a minute has passed.

### What Devices Use Propagation Delay?

A lot of the devices we use today use propagation delay. Some of these systems are:

• Routers: The devices that let us access the Internet by connecting our computers to them either in a wired manner or wirelessly.
• Massively multiplayer online role-playing games (MMORPGs): Online games that several players can join in at the same time so they can play as either team mates or opponents.
• Application-specific integrated circuits (ASICs): Integrated circuit chips customized for a particular use rather than intended for a general purpose.

As you can see from the examples above, propagation delay applies to practically any device that has integrated circuits. An integrated circuit refers to a set of electronic circuits made into a chip using a small flat piece of semiconductor material, usually silicon. It looks like this:

From what you’ve learned about propagation delay in this post, you can ascertain that it applies to practically any computerized or digital gadget you own. It also applies to all electronic appliances.