Learn About Xfinity® High-Speed Internet

Xfinity
Heard about Xfinity? Learn more now!

E-mail
Setting up and using Comcast email.

Security
Download the Norton Security Suite, learn more about Phishing and Spam, and how to protect your PC.

Account Management
Learn how to manage your Comcast High-Speed Internet accounts as well as how to change your Comcast password.

DOCSIS 3.0 - Comcast's fastest fast speeds
Details about Comcast's new speeds and information about the DOCSIS 3.0 program

Home Networking
Information about home networking and Comcast wireless routers.

Features and Services
Learn about Comcast's newest Features and Services.

New Comcast Customers
New to Comcast? Learn more about us here.

What must be installed to use Xfinity Speed Test?

XFINITY Speed Test should work in any web browser that supports Flash. At least Flash 8 is required to use the current version of XFINITY Speed Test. Those with a version earlier than 8 will not be able to use the application. We recommend using the most current version of Flash available.

JavaScript is also used heavily throughout the site (even to display the Flash), so make sure you don't have it disabled!

How do I get the most accurate speed test results?

Xfinity Speed Test gives the most accurate results when you are connected to the internet via a direct cable from your computer to your cable modem.

Connections which rely on wireless signal strength may have varying results that do not represent the full potential of your service.

What is the best way to use Xfinity Speed Test?

To best utilize Xfinity Speed Test, find the server that provides the fastest and most consistent results, then test against that server frequently to identify trends and make sure you are getting what you expect from your connection. In most cases, the server with the shortest physical distance from your location will be have the best results.

How does Xfinity Speed Test work?

The Xfinity Speed Test operates over multiple TCP sessions. The TCP session makes use of Port 80 & Port 5050. The three stages of the test are Ping, Download, and Upload.

Ping (Latency) Test

This test is performed by measuring the time it takes to get a response for a TCP request sent to the server. It is done 10 times with the average value determining the final result.

Download Test

A small binary file is downloaded from the server to the client to estimate the connection speed. Based on this result, one of several file sizes is selected to use for the real download test. The download test is performed with cache prevention via a random string appended to each download. Speed is measured up to 30 times per second. Ordered samples are looked at through a sliding average window to eliminate anomalies and determine the result.

Upload Test

A small amount of random data is generated in the client and sent to the server to estimate the speed of the connection. Based on this result, an appropriately sized set of randomly generated data is selected for upload. The upload test is then performed in chunks which are pushed to the server. An overall average is used to determine the result. The Speed Test is a true measurement of speed between the web server and client.

HTTP Fallback

In the case that TCP Port 5050 is not available, the Speed Test will fall back to using HTTP on Port 80. You may notice a slight delay when initiating a test.

Why does Xfinity Speed Test say I need at least Flash version 8 when I already have it?

Xfinity Speed Test uses JavaScript to detect your Flash version. If you are certain that JavaScript is enabled, then there could be an error in your Flash installation. This problem is usually solved by uninstalling and then reinstalling Flash.

Why does the download test work, but the upload does not (or vice versa)?

This is usually the result of something installed on your computer that is intercepting traffic between your web browser and the server.

Examples of this would be security software from ZoneAlarm, McAfee, or Symantec.

Try momentarily disabling the software to see if it is the source of the problem. Make sure you don't leave it disabled! Any software firewall should work with Xfinity Speed Test if configured properly. As an example, if using ZoneAlarm you must make sure that none of the boxes are checked in the custom cookie control menu.

What do my speed test results mean?

8 Kilobits (Kb) = 1 Kilobyte (KB)
8 Megabits (Mb) = 1 Megabyte (MB)
KB and MB are measurements of data file sizes and storage.


Kbps and Mbps are short for "Kilobits per second" and "Megabits per second" and are measurements of data transfer rates (also known as connection speed).


To estimate how long it takes to download a large file based upon your connection speed, you can use the following mathematical equation: (Convert file size to Mb) / connection speed (in Mbps) = # of seconds to complete download. For example, if your connection speed is 16 Mbps, then you could theoretically download a 2 MB file in approximately one second. (2 MB x 8 Mb) / 16 Mbps = 1 second

What is ping and how is it measured?

Ping on Xfinity Speed Test is a bit different than a traditional command-line ping which uses ICMP. We are measuring the time it takes to get a response for a TCP request sent to the server.

The number may be higher than an ICMP ping, but the relative value to other tests is still very useful. The server with the lowest ping will usually be the server that provides the most accurate speed test results.

Why am I seeing two results for downstream speed and two results for upstream speed?

The latest version of the Xfinity Speed Test allows Xfinity customers to test against two distinct network protocols: IPv4 and IPv6. Xfinity is the industry leader in the deployment of the new, next generation internet protocol IPv6. Where available, two distinct sets of speed results will be provided. As IPv6 is currently being deployed across the Xfinity footprint, not all Xfinity customers will see two sets of speed results. For more information on the Xfinity IPv6 deployment, please visit our IPv6 information page at www.comcast6.net.

What is the difference between speed tests performed over IPv4 vs IPv6?

The latest version of the Xfinity Speed Test allows Xfinity customers to test against two distinct network protocols: IPv4 and IPv6. IPv4 and IPv6 speed testing is performed the same way, calculating your speed based on file transfers to and from a specific server. The only difference between these tests is which network protocol is used: IPv4 or IPv6. For more information on the Xfinity IPv6 deployment, please visit our IPv6 information page at www.comcast6.net.

Why is this speed test showing faster speed results than other tests?

The results from Xfinity Speed Test represent an estimate of the maximum connection speeds for downloading and uploading a file size between 256KB and 100MB.

There are a number of other variables which could impact your speed test results from a third party test site. For example, when using a 3rd party speed test site, your traffic may travel over networks that are not controlled by Comcast. Those "peering" networks may have an effect on the overall speeds. In addition, the 3rd party's test engines could be using a single threaded TCP connection during testing. This counteracts the ability to reach higher speeds, as there is more wait time from the packets being sent and received from the 3rd party speed test server. Our speed test server is running 4 simultaneous threads, which is modeled to reflect normal browsing across currently available websites. Also, the 3rd party site may not be using test files that are large enough to permit an accurate reading for speed tiers with higher speeds.

Actual speeds may vary and are not guaranteed.

How does Xfinity Speed Test know where I am?

Xfinity Speed Test uses GeoIP data from MaxMind to determine your location. It then calculates your current distance from the server you selected.

Why doesn't the closest server provide the best speed results?

The internet does not operate in direct paths. To reach a Speed Test server, your traffic may not be routed in a direct line to the server's geographical location. This increased distance may result in increased latency which may impact your test results.

Obtain the best test results by trying several different servers.

Why does network distance affect speed?

You have likely noticed that downloading from a local server location is faster than a distant one. This is because the TCP window is not optimized for the increased latency that comes from an increase in distance.

The TCP window size determines how many packets can be sent at one time. The larger the window size, the higher the speeds. Increased latency decreases the TCP window size.

Does Comcast guarantee my service will achieve my subscribed speeds?

No. Neither Comcast nor other ISPs will guarantee that specific speeds will always be available. While Comcast provisions its network to provide up to the maximum speed available with your service, a number of factors affect speed and the actual speeds you receive may vary. Many of the factors affecting speed are beyond Comcast's control. For example, speed can be affected by the type of computer you have, the processing capacity of your computer, the applications running on your computer, and the nature of your home network connection. In addition, the websites you visit, the capabilities of third party networks, and congestion on the internet may affect internet speeds.

Why would the capabilities of a website or a third party network affect my speeds?

Various websites cap the speeds at which consumers are permitted to download or stream content. Those websites may also become congested, which could further slow your connection to that website.

The internet has been described as a "network of networks." Comcast's network is interconnected with the networks of a number of third parties and Comcast can only control the services on its own networks. If a third party's network is congested or has other limits on speed, you may not be able to achieve your provisioned download speeds to that specific website.

Why are my wireless connection speeds slower than my wired connection speeds?

There are many variables that could impact your speed when connected to the internet through a wireless network. For example, microwaves, static electricity, fluorescent lights, windows, wall type and thickness, distance, band and signal settings, multiple devices on the same channel, and several other factors can impact the speeds you receive when wirelessly connected to the internet. These WiFi variables can add substantial delay which may result in speed degradation. A wired connection eliminates many of the potential variables of a wireless network, resulting in improved performance. Comcast advises using a RJ45 CAT5E Ethernet cable to connect to your cable modem or router to ensure the best possible performance. An RJ45 CAT5E cable should have been provided during your installation.

Does the location of my wireless gateway or router affect WiFi performance?

Yes, for optimal performance, place the wireless gateway or router in:

Areas to avoid include:

Why does my WiFi speed performance vary?

WiFi performance can vary due to many factors such as:

I received a notification from Comcast that my speeds have been increased, but this is not reflected in my Speed Test results. Why is this?

In order to complete your speed increase, you will need to reset your cable modem. Instructions for resetting your cable modem can be found via the following link: www.comcast.com/powercycle.

If you are still not receiving your expected speeds after you have reset your cable modem, you may need to upgrade your cable modem; to confirm, please visit mydeviceinfo.comcast.net.

What are the minimum system requirements for my speed tier?

Please visit the Xfinity High Speed Internet requirements website to review the minimum system requirements for your speed tier.

We advise using the latest version of your preferred web browser to ensure optimal performance.