The Design of Repeatered Lines for Long-Haul Coaxial Systems

Repeatered line design for long-haul coaxial systems centers about the equalization of the 4000-mi (6400-km) cable loss. In the L5 system, which provides 10 800 toll grade quality message channels on a pair of 0.375-in (9.5-mm) coaxials, this loss is over 120 000 dB at the highest message frequencies and is compensated with a variety of fixed and adjustable equalizers distributed along the coaxial line. This equalization must be achieved while at the same time providing an adequate signal-to-noise ratio. The significant properties of the coaxial medium and how they affect the "hierarchy" of equalizers traditionally found in long-haul coaxial systems are described. The manner in which the various levels of equalization relate to each other and to the fundamental transmission phenomena within the system is considered at length. The paper begins with a discussion of the evolution of highcapacity systems and the particular role that the L5 system is expected to play in future long-haul system planning.     

Switched digital capability: An overview

SDC (Switched Digital Capability) allows end-to-end circuit-switched 56 kb/s data over much of the existing Bell System Network. Since SDC is based largely on the stored program-controlled space and time-division switches, 2-wire local loops, and T-carrier facilities that are already deployed in the network, it can be realized with minimum modification to the existing network. SDC is expected to play a major role in the evolution of the present network to the ISDN (Integrated Services Digital Network) of the future.