What is network latency?

Send a child to the shop at the corner for salt, and count the seconds until they are back at your door. That round trip is latency.

Now send the same child with a large basket. The basket decides how much salt comes back in one trip, and that is bandwidth. The two are different things, and people mix them up every day.

Networks behave the same way. Latency is the wait, and bandwidth is the load. Therefore, a wide line with a long wait still feels slow.

What latency actually measures

Latency is the delay between sending something and getting an answer. On a network it is normally measured as a round trip. Your device to the far computer, then back again.

The unit is the millisecond, written as ms. One millisecond is one thousandth of a second. Ten of them pass faster than a blink.

The usual tool for measuring it is called ping. Ping sends a tiny message, waits for the reply, and prints the time. If ping says 40 ms, the round trip took forty thousandths of a second.

Latency and bandwidth are different

Bandwidth is how much data fits through the line each second, and latency is how long the first bit has to wait. Raising one does not fix the other.

Picture a lorry loaded with hard drives, driving from Nairobi to Mombasa. Its bandwidth is enormous, but its latency is hours. Nobody would use it for a phone call.

This is why a bigger bundle does not always help. If your video call stutters, look at the wait before you pay for more bandwidth.

What the delay is made of

Four things add up to the number ping shows you.

• Distance. The signal has to cross the ground, and that takes time.
• Queueing. Data waits in line inside routers when the road ahead is busy.
• Processing. Every device on the path reads the address on each packet and decides where to send it.
• Loading. Pushing the bits onto the wire takes time, and a slow link takes longer.

Queueing is the part that changes minute by minute. At eight in the evening, when the whole street is watching video, queues grow and your ping rises. Nothing broke, and the queue simply got longer.

Why distance sets a hard floor

Light inside a glass fibre travels about 200,000 kilometres per second. That is fast. However, it is not instant.

Nairobi and London sit about 6,800 kilometres apart in a straight line. A round trip covers double that. Even in perfect glass, that comes to roughly 70 milliseconds. Real cables bend around coasts and borders, so the true figure is usually well above 100 milliseconds.

No upgrade beats this, because you cannot pay for a faster speed of light. THE ONLY CURE FOR DISTANCE IS TO MOVE THE CONTENT CLOSER.

Where you feel it

Voice calls feel it first. Engineers try to keep the one-way delay under about 150 milliseconds. Past that point, two people start talking over each other.

Games feel it next. A player at 30 ms sees the action sooner than a player at 200 ms, and wins fights they should have lost.

Web pages feel it in a quieter way. This is because one page may fetch dozens of separate files, and each fetch pays the delay again. Therefore a page held on a distant server can crawl even on a wide line.

Factories and hospitals care most of all, because a robot arm needs its answer in a few milliseconds, every single time. This is one reason 5G was built to answer faster than 4G, and why 6G work pushes in the same direction.

Jitter and loss

Latency is not the only number worth reading, and jitter is the wobble in that number. If your ping jumps between 20 and 300 milliseconds, calls will break up even when the average looks healthy.

Packet loss is the third number, and it counts the messages that never arrive at all. A lost packet has to be sent again, and the resend costs another full round trip.

So read the three together. A steady 60 milliseconds beats a jumpy 30.

Why some places wait longer

Kenya shows the pattern well. Undersea fibre cables come ashore at Mombasa and carry traffic inland to Nairobi. If the website you want sits in Europe, your request travels that whole road, twice.

Kenya also runs an exchange point in Nairobi, a place where local networks meet and hand traffic to each other. Before such places existed, a message between two networks in the same city could travel to Europe and back. The distance was pointless, but the delay was real.

Today the large platforms keep copies of popular content inside the country. The video you watch may already sit on a machine in Nairobi. That is why some sites feel quick and others feel slow on the very same line.

Satellites change the sum again, because a satellite parked high above the equator adds more than half a second to every round trip. However, newer satellite internet flies far lower and cuts that to tens of milliseconds.

How to measure your own

Open a terminal and type the word ping, then a website name. Watch the numbers for one minute, and note the lowest, the highest, and how often a reply goes missing.

Then run the same test in the evening and compare. If the wait doubles once the neighbourhood comes home, you are sharing a crowded link. A bigger bundle will not fix that.

Just Out Tech explains new research in plain language. This article was drafted with AI assistance and checked by a human against the original source.