:: Speed with a cable modem

The speed of data transfer achieved through the cable modem can be characterized in two different ways, upstream and downstream.

Upstream is when data is transferred from the computer to the network, whereas Downstream is data transfer from the network to the computer.

The downstream channel has a much higher bandwidth allocation (faster data rate) than the upstream, primarily because Internet applications tend to be asymmetric in nature. Activities such as World Wide Web (http) navigating and newsgroups reading (nntp) send much more data down to the computer than the other way round. Mouse clicks (URL requests) and e-mail messages are not bandwidth intensive in the upstream direction. Image files and streaming media (audio and video) are very bandwidth intensive in the downstream direction.

In the downstream direction, network speeds can reach 30 Mbps, an aggregate amount of bandwidth that is shared by users. Few computers will be capable of connecting at such high speeds, so a more realistic number is 1 to 3 Mbps. In the upstream direction, speeds can be up to 10 Mbps. However, most modem producers have selected a more optimum speed between 500 Kbps and 2.5 Mbps. Some service providers limit upstream access speeds to 256 Kbps or less.