The term is relative since a backbone in a small network could be much smaller than non-backbone lines in a large network.
Return link in a two-way data circuit, such as a coaxial cable or satellite circuit.
The bandwidth of this upstream channel is usually less than that of the forward channel. Range of frequencies between two defined limits. For example, the audio band, the range of frequencies that can be detected by the human ear, ranges between about 20 and 20,000 Hertz. Generally, the larger the bandwidth, the greater the capacity of voice, video, or data the media can carry. Bandwidth in systems is limited both by the transmission media and by the electronics sending and receiving data.