How Do Cable Companies Limit Your Internet Speed?

By Milton Kazmeyer

Cable ISPs can use a variety of techniques to throttle your bandwidth.
i Hemera Technologies/ Images

When you subscribe to cable Internet service, your service provider transmits data to your computer using the same coaxial cable used to transmit television programs to your home. Typically, you subscribe to a line that offers a certain data speed, such as 20 megabits per second, and you can download data up to that limit as far as network congestion allows. In certain circumstances, however, your ISP may artificially limit your Internet use, either reducing your overall speed or slowing down certain services.

Speed Limits

In most cases, the speed limit of your connection is set inside your cable modem. The hardware contains configuration options that can increase or decrease the data transfer speed. This allows your service provider to sell multiple levels of service, offering faster speeds to customers willing to pay for the privilege. In the past, some cable modem designs were prone to hacking, allowing users to "uncap" their connections and receive vastly faster transfer speeds than the service provider intended. Modern cable modems are much harder to manipulate, and ISPs can scan for unauthorized activity to identify anyone trying to alter their hardware.

Peak Use and Congestion

In the early days of the Web, high-speed connections were much faster than most people required. Even when connections were only a few megabits, most content was text or low-resolution images, so most users never came close to pushing the limits of their connections. The growth of streaming video, peer-to-peer file sharing and other high-bandwidth applications has put a considerable strain on Internet service providers, and many networks suffer congestion and slowdowns during peak usage periods as large numbers of users attempt to access content simultaneously. To combat this, some ISPs use systems that slow down connections gradually during peak usage hours, in order to allow everyone some access to the network.

Traffic Shaping

Another way cable companies limit Internet speed is through traffic shaping. These systems monitor the packets that flow through the network, attempting to identify the services using those packets. If the system detects a peer-to-peer file transfer, for instance, it can throttle that activity, slowing it to a crawl without affecting the speed of streaming video or other applications. Using non-standard ports or encryption can defeat these types of systems, however.

Bandwidth Caps

In order to combat high bandwidth usage by customers, many ISPs have introduced bandwidth caps. The system allots you a certain amount of data transfer every month, and if you go over that allotment, you can incur additional charges or even have your service terminated. Some ISPs use a system that monitors your data transfer and once you download or upload too much data, it slows your connection down significantly. In some cases, this may only be for a few days, while in others, it may remain slowed until your next billing cycle begins.