Compare asymmetric communications.
In telecommunications, the term symmetric (also symmetrical) refers to any system in which data speed or quantity is the same in both directions, averaged over time. Examples include two-way radio, standard twisted-pair telephone Internet connections, cable modem Internet connections in which the cable is used for transmission as well as for reception, and full-motion videoconferencing.
Symmetric communications is not necessarily the most efficient mode in a given application. Consider casual Web browsing, in which most of the bytes come downstream (from Internet servers to the user) as relatively large graphics, sound, multimedia, and HTML files, while upstream data (from user to a server) consists mainly of new link (URL) requests by the user, which, in comparison, contain few bytes. In this environment, it often makes the best use of available resources to supply the user with a more broadbanded "pipeline" in the downstream direction, as compared with the upstream direction.
The ultimate Internet connection is broadband symmetrical, such as is provided by true cable modem connections and optical fiber systems. At the time of this writing, symmetric broadband is not generally available outside of metropolitan areas.