Latency Part I

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Introduction

While bandwidth is the amount of data that can be transmitted over a connection in a given amount of time, latency refers to the delay or amount of time it takes for data to travel from one point to another across network. ?It is often measured as the time difference between when a device sends a request for data and when it receives the requested data. ?Latency is a way to measure speed or the time delay it takes to send information from one point to another.? It is measured as some amount of time, usually in milliseconds.? Latency is an important factor in determining the quality of an Internet connection and can significantly affect customer’s Quality of Experience (QoE). ?A network with high latency will have slower response times, while a low latency network will have faster response times.

A review of the research literature reveals that a commonly agreed definition of latency does not exist.

Though in principle data should traverse the Internet at nearly the speed of light, in practice, data packets move across the Internet at a slightly slower rate due to delays caused by distance, Internet infrastructure and other variables. ?The sum of these time delays comprises a network’s latency.

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We will discuss several articles in the Latency to show impact of Internet Services for customers, Telecom Operators and Internet Service providers.? In this article we will start with demystifying Internet Speed:

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1.???? Demystifying Internet Speed Term.

2.???? Factors Causes Internet Latency.

3.???? Impact of Latency on Internet Applications.

4.???? Techniques to Manage Latency.

5.???? Conclusions.

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Demystifying “Internet Speed” Term?

Bandwidth is a measure of the volume of data that can pass through a network at any given time. It is measured in data units per second usually megabits per second (Mbps), and is likely the measurement you’re used to hearing about (Internet Speed) from your service provider when choosing connection options for your home or office. This is a source of great confusion, as bandwidth is not a measure of speed but of capacity. While high bandwidth can facilitate high internet speed, that capability is reliant on factors like latency.?

Consider the following analogies:?

A.??? If you internet Service Provider (ISP) has assigned you a 5 megabit per second (5Mb) link for you (this represent bandwidth)

And if you are using 3G technology (your connection 3G), the latency will be ~100ms, but if you are using 5G technology (your connection 5G), the latency will be ~10ms instead.

Outcome:

1.???? If you are downloading a big file, you will notice a small different in speed time as download apps are not latency-sensitive.

2.???? If you are browsing, you will feel a noticeable different in speed as Browsing apps are interactive in nature and latency-sensitive.

3.???? If Your connection latency +800ms, everything’s will collapse and your internet speed will be very slow regardless of your bandwidth amount.

So, latency matters.?

B.??? The overall internet speed can be considered as a function of both bandwidth and latency.? A simplified equation might look like this:

Internet?Speed = f(Bandwidth / Latency)

Other factors contribute to the internet speed, such as distance, network congestion, the efficiency of the communication protocol and the responsiveness and number of servers and network devices.

Examples:

1.???? A person can define his Internet speed link as 5Mb over 5G

2.???? A person can define his Internet speed link as 5Mb over ADSL

3.???? A person can define his Internet speed link as 5Mb over 3G

4.???? A person can define his Internet speed link as 5Mb over 4G

The overall performance and responsiveness of the above examples are different

C.???? Bandwidth is the amount of storage space in the car and latency is the speed of the car.

D.??? High bandwidth is better. Low latency is better.

E.???? To give you an idea of internet latency values: ?It takes about 250 milliseconds for an object dropped from a tabletop that is one meter high to reach the ground, which is much longer than the time it takes for data to travel over the internet for a distance of 2000 km, which will take ~10 milliseconds.

F. Bandwidth vs Latency

Now, let's be clear, higher bandwidth is never a bad thing, especially for use cases that require bulk transfer of data, however, when it comes to your web browsing experience, it turns out that latency, not bandwidth, is likely the constraining factor today. ?As a customer, did you consider this when you picked your ISP? Likely not, I'm yet to see any provider mention, yet alone advertise latency.

Akamai's State of the Internet stats show that as of 2011 an average US consumer is accessing the web on a 5Mbps+ pipe. In fact, with the fast growth of broadband worldwide, many other countries are hovering around the same number, or quickly catching up. As it happens, 5mbps is an important threshold.

The two graphs below show the results of varying bandwidth and latency on the page load time (PLT). ?Upgrading your connection from 1Mbps to 2Mbps halves the Page Load Time (PLT), but quickly thereafter we are into diminishing returns. In fact, upgrading from 5Mbps to 10Mbps results in a slit improvement in page loading times. ?In other words, consumer would not benefit much from upgrading their connection more than 5Mbps when it comes to browsing the web.? However, the latency graph tells an entirely different story. For every 20ms improvement in latency, we have a linear improvement in page loading times. There are many good reasons for this: ?An average page is composed of many small resources, which require many connections, and TCP performance of each is closely tied to Round Trip Time (RTT).

If we want a faster browsing experience then reducing the Round Trip Time (RTT) should be near the top of our list.

We are led to conclude that an average consumers would not benefit much from upgrading their bandwidth more than 5Mbps if they are interested in improving their web browsing speed. They may be able to stream or upload larger media files more quickly, but the pages containing those files will not load noticeably faster: ?Bandwidth doesn’t matter, much.

Analogy from the above figure:

If you have connection speed 5Mbps and latency 20ms, Page Load Time (PLT) = 1,000 ms, and if you have connection speed 10Mbps and latency 140ms PLT = 2,500 ms, so why I have to pay for 10Mb instead of paying for 5Mb if the 5Mb operator latency less.

This analogy shoes that if you increase the bandwidth more than 5Mb, there will be no noticeable change in Page Load Time (PLT), but if you reduce latency, there is noticeable change in Page Load Time (PLT), hence better performance and responsiveness.

So, connection speed with 5Mb + 20ms much better than connection speed with 10Mb + 140ms in case of web browsing.

Studying of Latency is directly related to Subscriber Quality of Experienced (QoE) discussed in my previous article https://www.dhirubhai.net/pulse/quality-experience-qoe-telecommunications-services-abdalla-elsiddig-1c/?trackingId=TjEZxTlHR9m75Z9ZZI8y2w%3D%3D