Upstream (computer science)
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The word upstream has several meanings in the field of computer science. The most common usage of the word refers to the speed at which data can be transferred from the client to the server (uploading). This differs greatly from downstream not only in theory and usage, but also in that upstream speeds are usually at a premium. Whereas downstream is important to the average home user for purposes of downloading content, uploads are used mainly for web server applications and similar processes where the sending of data is critical. ADSL and Cable modems are asymmetric, thereby rendering the upstream speed to be much lower than that of its downstream. Symmetric connections such as SDSL and T1, however, offer identical upstream and downstream speeds.
Upstream has gained great relevance with the use of P2P software.
If a node A in the Internet is closer (fewer hops away) from the Internet backbone than a node B, then A is said to be upstream of B or conversely, B is downstream of A. Related to this is the idea of upstream providers. An upstream provider is usually a large ISP that provides Internet access to a local ISP. Hence, the word upstream also refers to the data connection between two ISPs.
Another less common meaning of the word upstream is used to refer to the core development of an Open Source project - e.g. an upstream patch is a patch targeted at being included in the project's main branch.
See also: Downstream
