DSLPro.com: Your DSL Performance Expert

Measuring DSL Performance

A fast, reliable Internet connection has become a “must have” for today’s Internet applications - including streaming video (for example Roku™ and Hulu™) and online gaming (Battelfield™, Call of Duty®, and other titles).

Yet when an Internet connection becomes slow or intermittent, then troubleshooting the source of the problem can be very challenging. Does the issue lie in the PC (or other device), in the home network, in the DSL link, or within the Internet itself?

If you are experiencing Internet connectivity issues, then the information below can provide some helpful guidelines for determining whether the problem may lie with the DSL link. In particular, if you experience the following problems, you may have a poor DSL connection:

• Unexpected pauses while watching a video
• Poor video image quality (especially when people or objects in the video are moving)
• Application delays when responding to commands (such as retrieving new mail or visiting a new Web site)
• Slow response time for online games (especially action games)

Continue to the sections below (DSL Measurements, Performance Test Option and Getting Accurate Results) to learn how you can reliably test your DSL and pinpoint any potential issues in your connection.

DSL Measurements

In general, three important measurements provide a good way to quantify the performance of a DSL broadband connection: throughput, latency, and stability.

Throughput measures the amount of data that can flow over the DSL link in a given amount of time, typically reported in Megabits per second (Mbps). Low throughput can affect the quality of a video stream (with unwanted pauses, or poor resolution), as well as how quickly you can download Web pages, email, or other data.

The throughput performance rating for DSL typically refers to the “downstream” throughput capacity, meaning the speed at which you can download data from the Internet. The “upstream” capacity of your DSL link measures the speed at which you can send data from your PC or other device. Typically, the downstream capacity of a DSL link is larger than the upstream link by design.

DSL connections today carry downstream throughput ratings from 256kbps to more than 50Mbps. Note: 1,000kbps = 1Mbps. DSL bonding allows the use of multiple lines in tandem to achieve even higher rates. Recently issued standards will lead to more ubiquitous 100Mbps to 1Gbps DSLs in the next few years (1GPS = 1,000Mbps).

What is the performance of my DSL connection?

Latency, typically measured in milliseconds (one one-thousandth of a second), represents the time required to send data from your home to another location on the Internet. Applications including VOIP (voice-over-internet-protocol, such as Skype) and online action games typically perform much better with lower latencies. VOIP operates best with latencies under 125 milliseconds. Online action games perform best at latencies under 50 milliseconds. Longer latencies can cause unwanted pauses or lags in your conversation or game.

Stability represents how well your DSL modem maintains a connection to your Internet service provider. An unstable DSL connection may result in data that gets “lost” or “corrupted.” Many applications can tolerate reasonable levels of lost and corrupted data. However, if it’s too unstable you may experience pauses, lags, and jumpiness in application performance. In the worst case, the DSL modem must retrain (reset) an unstable DSL connection. The retrain process can interrupt Internet access anywhere from 5 seconds to 30 seconds.

Performance Test Options

Several free services on the Internet allow you to measure the performance of your Internet connection. Here are just two:

www.speedtest.net: measures the downstream and upstream throughput of your Internet connection.

www.pingtest.net: measures the latency (the time it takes to send data from your PC or other device to a remote location on the Internet) and packet loss (a good measure of the stability of your Internet connection).

Some DSL modems and gateways also offer a built-in measure of DSL performance and stability (but unfortunately not latency). The modem’s software administration console commonly reports what is called a sync rate, typically displayed as “downstream/upstream rate” or “downstream/upstream connection speed.” The sync rate represents the maximum possible throughput of the DSL link. The actual DSL throughput is almost always smaller than the sync rate (just like the actual gas mileage of your car is almost always less than the mileage advertised by the manufacturer).

The DSL modem administration console may also include information about line stability (measured in terms of “link retrains” for example, meaning that the modem must re-establish a DSL connection over the phone line). Refer to the user manual of your DSL modem for details. If you do not have a printed copy of the user manual, you can often find an electronic copy on the modem manufacturer’s Web site.

Getting Accurate Results

What is the performance of my DSL connection?

Broadband performance tests measure the quality of the Internet link between two endpoints:

1. the device in the home that is running the test (typically a PC, Mac™, tablet, or smartphone)
2. a performance test server located on the Internet

The link between these two endpoints contains several different “segments,” such as a Wi-Fi network, the DSL connection, and several links (or hops) across the Internet cloud.

To obtain an accurate measure of performance for the DSL link alone, you must eliminate, or minimize, any impact from the other portions of the network connection. So for instance, if you suspect spotty Wi-Fi performance then connect the PC directly to the modem/gateway, rather than use Wi-Fi.

Likewise, to minimize the effect of any performance bottlenecks in the cloud, you must minimize the distance to the remote server. Performance test services such as speedtest.net use multiple servers throughout the world and automatically connect to the nearest server.

When running the performance test, be sure you have little or no Internet traffic from other users or devices in your home.