Main Page | See live article | Alphabetical index In telecommunication, the term available line (useful line) has the following meanings: In voice, video, or data communications, a circuit between two points that is ready for service, but is in the idle state. In facsimile transmission, the portion of the scanning line that can be specifically used for image signals. Source: from Federal Standard 1037C and from MIL-STD-188 This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License.