What is Network Latency?

Ken Black

Network latency is simply defined as the time delay observed as data transmits from one point to another. Usually, to determine this time delay, the origin and destination points are used. In some cases, network latency may be defined by the time it takes some form of data to make a full circuit back to the originating point.

Network latency, often referred to as "lag," is the time delay that happens as data packets transmit from one point to another over a network.
Network latency, often referred to as "lag," is the time delay that happens as data packets transmit from one point to another over a network.

While it may seem counterproductive to use the round-trip time, it actually can be a much better measure of overall network performance. This is because computers in the process of sending and receiving bytes are in constant communication with each other. Even the one receiving will send information back to the sending machine. Therefore, latency can easily be determined by the round trip time.

At times a router can even contribute to network latency.
At times a router can even contribute to network latency.

The main assumption in network latency is that the time of transmission between the origin and destination should be instantaneous. Of course, there will always be some delay. Even transmission at the speed of light is not instantaneous and can be measured with very precise instruments. Therefore, data on the time delay should always be available.

There are a number of factors that contribute to network latency. These include transmission, propagation, routers and computer hardware delays. In some cases, there may not be a delay the user can notice. Fortunately, if latency does become a problem, there are things that can be done to improve the situation.

In network latency, transmission refers to the medium used to transmit the information. This may be a phone line, fiber optic line or wireless connection, just to name a few examples. Each will contribute to the delay in some way. Some may be faster mediums than other. To help reduce latency, it may be possible to change the medium to a faster type.

Propagation is one of the harder things to control in network latency. Simply put, this is the physical distance between the origin and destination. Naturally, the greater the distance, the more delayed the transmission will be. However, this does not usually cause a significant delay.

The other contributors to network latency, routers and computer hardware, may be able to be changed. In those cases, upgrading this hardware can help process information faster, thus speeding up the process. While this may involve a substantial investment, the benefits may be worth the investment, depending on how much and how often data is transferred.

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Discussion Comments


@SkyWhisperer - In the telecommunications industry network latency is one of the chief concerns for services that use the Voice Over Internet Protocol. This is a packet-based approach to sending phone calls. The voice transmissions are chopped up and bundled into packets and then put back together on the other end of the call. When there is latency, the packets don’t arrive at the destination at the same time. This causes the familiar delay that people who use these services complain about.

Latency has improved over the years so that now these phone calls sound as clear as regular calls, with virtually no latency.

Engineers use a network latency simulator and do some other calculations with network bandwidth usage to improve the efficiency of the network and improve phone call quality. But as you mentioned, you’re still using the Internet so if there are Internet latency issues then no doubt it will affect call quality.


I work in networking and have to test things like network latency all the time. In case you're interested, a simple network latency tool to conduct such a test is the DOS command ping. Go to your DOS command line, type ping and the I.P. address of the website you are checking and hit enter. The ping tool will send off a request to the website, and you’ll see a list of statistics being returned back which indicates whether the test timed out or not, and the time it took to return the values. This number is your network latency figure. In a nutshell, 100ms or less for this is considered good.

If you get back anything more than this then you have latency issues. The tool doesn’t tell you what caused the latency only that it’s there. You may want to contact your I.S.P. to see if there are any outages or serious congestion issues which are slowing down the network. Of course if you get back a message that the network timed out, then it’s pretty certain you have no Internet connection and that’s where you should begin your troubleshooting.


How do they test network latency? Do they only do it when the system is so slow that it is bothersome?

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