What Causes Network Lag and How to Fix It

Why Your Internet Is So Slow

Young computer worker buried in network cables, holding plug

David Samuel Robbins / Getty Images

The latency of a network connection represents the amount of time required for data to travel between the sender and receiver. While all computer networks inherently possess some form of latency, the amount varies and can suddenly increase for various reasons. People perceive these unexpected time delays as "lag."

High latency can also cause high delays. For example, your video game might experience high latency which causes the game to freeze at times and not deliver a live update of the other players. Fewer delays would mean that the connection is experiencing lower latency.

Network lag happens for a few basic reasons, namely distance and congestion. In some cases, you might be able to fix internet lag by tweaking how your device interacts with the network.

Office worker in a tangle of cables.

Latency and Bandwidth

Latency and bandwidth are closely related, but they're two separate terms for a reason. To understand what causes high latency, it's important to differentiate it from high bandwidth.

If your internet connection were illustrated as a pipe carrying data, bandwidth would refer to the physical size of the pipe. A really small pipe (low bandwidth) can't hold much data at once, while a thick one (high bandwidth) is able to transmit much more data at a time. Bandwidth is often measured in Mbps.

Latency is simply a delay, measured in ms. It's the time it takes for information to move from one end of the pipe to the other. It's also called the ping rate.

The Speed of Light on a Computer Network

No network traffic can travel faster than the speed of light. On a home or local area network, the distance between devices is so small that light speed doesn't matter. For internet connections, however, it becomes a factor.

Under perfect conditions, light requires roughly 5 ms to travel 1,000 miles (about 1,600 kilometers). Furthermore, most long-distance internet traffic travels over cables, which can't carry signals as fast as light due to a principle of physics called "refraction." Data over a fiber optic cable, for example, requires at least 7.5 ms to travel 1,000 miles.

Typical Internet Connection Latencies

Besides the limits of physics, additional network latency is caused when traffic is routed through servers and other backbone devices. The typical latency of an internet connection also varies depending on its type.

The study Measuring Broadband America (posted in late 2018) reported these typical internet connection latencies for common forms of U.S. broadband service:

  • Fiber optic: 12-20 ms
  • Cable internet: 15-34 ms
  • DSL: 25-80 ms
  • Satellite internet: 594-612 ms

How to Fix Latency

Latency can fluctuate in small amounts from one minute to the next, but the additional lag from even tiny increases can be noticeable. The following are common reasons for internet lag, some of which are completely out of your control:

Overloaded Router/Modem

Any router will eventually bog down if too many clients are using it at the same time. Network "contention" among multiple clients means that they are sometimes waiting for each other's requests to be processed, causing lag.

You could replace the router with a more powerful model, or add another router to the network to help alleviate this problem. Similarly, network contention occurs on a residence's connection to the internet provider if saturated with traffic.

Depending on the speed of your connection, try to avoid too many simultaneous downloads and online sessions to minimize this lag.

Overloaded Client Device

PCs and other client devices also become a source of network lag if unable to process network data quickly enough. While modern computers are sufficiently powerful in most situations, they can slow down significantly if too many applications are running simultaneously.

Even running applications that don't generate network traffic can introduce lag; for example, a misbehaving program can consume 100 percent of the available CPU, which delays the computer from processing network traffic for other applications.

Malware

A network worm hijacks a computer and its network interface, which can cause it to perform sluggishly, similar to being overloaded. Running antivirus software on devices connected to the network helps to detect and remove these worms.

Use of Wireless

Online gamers, as an example, often prefer to run their devices over wired Ethernet instead of Wi-Fi because Ethernet supports lower latencies. While the savings is typically only a few milliseconds in practice, wired connections also avoid the risk of interference that can result in significant lag.

No Local Cache

One way to reduce latency is to utilize caching in your browser, which is a way for the program to store recently used files so that you can access them again locally the next time you request them (no download necessary).

Most browsers will cache files by default, but if you delete the browser cache too often, you'll notice that it takes longer to load the same pages you were just visiting.

Some latency issues can be fixed, but the following are latency issues that aren't usually in your control.

Traffic Load

Spikes in internet utilization during peak usage times of day often cause lag. The nature of this lag varies by service provider and a person's geographic location. Unfortunately, other than moving locations or changing internet service, an individual user can't avoid this kind of lag.

Online Application Load

Online multiplayer games, websites, and other client-server network applications utilize shared internet servers. If these servers become overloaded with activity, the clients experience lag.

Wireless Interference

Satellite, fixed wireless broadband, and other wireless internet connections are particularly susceptible to signal interference from the rain. Wireless interference causes network data to be corrupted in transit, causing lag from re-transmission delays.

Lag Switches

Some people who play online games install a device called a lag switch on their local network. A lag switch is specially designed to intercept network signals and introduce significant delays in the flow of data back to other gamers connected to a live session. You can do little to solve this kind of lag problem other than avoiding playing with those who use lag switches; fortunately, they're relatively uncommon.

How Much Lag Is Too Much?

The impact of lag depends on what you're doing on the network and, to some degree, the level of network performance that you've grown accustomed to.

Users of ​satellite internet expect very long latencies and tend not to notice a temporary lag of an additional 50 or 100 ms. Dedicated online gamers, on the other hand, strongly prefer their network connection to run with less than 50 ms of latency and will quickly notice any lag above that level.

In general, online applications perform best when network latency stays below 100 ms; any additional lag will be noticeable to users.