Remreed Switching Networks for No. 1 and No. 1A ESS: Transmission Design and Environmental Protection of Remreed Networks

The switching network of a telephone central office serves the function of interconnecting the many lines and trunks of the office with each other and with service circuits such as tone sources, signal transmitters, signal receivers, etc. For the duration of the connection, the switching network constitutes a portion of a transmission channel over which communication takes place. The remreed network for No. 1 and No. 1A ESS is a space-division metallic network. The transmission channels are formed by interconnecting metallic conductors with metallic contacts, and electrical isolation of different channels is achieved by physical separation in space. The remreed network is also classified as a two-wire network since, for each connection, two independent metallic-conductor paths are established: the so-called tip (T) and ring (R) conductors. 637 In the ideal case, the T and R conductor paths of a remreed network would form a noninteractive extension of the office cabling appearing at the network terminals. The electrical isolation between channels would be complete (infinite coupling loss), and the transmission channel would contain no internal noise sources. Furthermore, this would ideally be true at all frequencies. Of course, this cannot be achieved in practice but can be approached sufficiently by careful design. The T and R conductors of the remreed network are extended into the outside plant of a telephone exchange area by cables. As a result, the remreed network is exposed to an electrically hostile environment.