Twisted pairs are familiar to all of us as the copper wire telephone lines. These are of low frequency, and support a limited bandwidth (one voice channel) but can also be used for data communication at the lower speeds of 300bps. For higher speed or rates of data transfer, 4-wire leased lines may be used. The problems associated with this kind of transmission are: noise on the line, parity errors and so on. Twisted pairs are used for conventional voice telephone and telex services.