What Factors Affect Cable Internet Speed With Comcast?

By Steve Lander

Your cable's physical condition affects its speed.
i Ryan McVay/Photodisc/Getty Images

Comcast's Xfinity service delivers a high-speed Internet connection over the coaxial cables that they have installed in millions of American households using a system called the Data Over Cable Service Interface Specification. Xfinity cable connections can be extremely fast, with download speeds reaching as fast as 105Mbps as of March of 2013. However, Xfinity cable connections are also finicky and many different factors can impact the actual speed that you see at your router.

The Package

Comcast sells different speed tiers. As of March of 2013, Comcast offers three tiers of speeds -- 6Mbps, 30Mbps and 105Mbps -- although these tiers can vary upwards or downwards depending on the physical plant in your area. If you only pay for the 6Mbps service, you won't get 105Mbps worth of bandwidth.

Upload or Download

Comcast Internet service, like most cable broadband, is asymmetrical. This means that it is designed to give you faster downloading speeds than uploading speeds. Since most users consume more content than they create, this is not a problem. However, you will notice this if you need to upload a great deal of data to other servers. The speed differences are built into both the DOCSIS standard and into how Comcast configures its network and assigns its cable bandwidth.


Comcast has a history of intentionally slowing down certain types of traffic over its network. For example, in 2012, they fell under investigation from the Federal Communications Communication for their practice of intentionally slowing down file transfers conducted using the BitTorrent protocol. Prior to the reduction in throttling, Comcast had been engaging in it for years and could, theoretically, restart it at any time.


Comcast cable Internet service is shared between multiple houses. Every house in a neighborhood connects to a device called a neighborhood node that then connects to Comcast's high-speed network. If most or all of the neighborhood gets online at the same time, the node can become overloaded and the Internet service of everyone that is connected will slow down.

Physical Conditions

The relatively simple coaxial cable that connects to your cable modem carries a staggering amount of data. Between television, telephony and Internet service, it's not uncommon for the cable to transmit over a gigabit of bandwidth. If the cable isn't in excellent physical shape, its data carrying capability goes down and your Internet speed will suffer. The same rule applies to its connectors and to the cable in Comcast's system as well.