Optical subscriber line transmission system to support an ISDN primary-rate interface

NTT'' 5 ISDN primary-rate interface services which employ the CCITT Recommendation I. 431 user/network interface use an economical optical subscriber line transmission system to cover both small and large exchange areas. DSU is miniaturized through LSI techniques and its cost is reduced by mainly using consumer components. Moreover an OCU installed in a subscriber line terminal for direct connection has the same unified internal interface for user information transmission and testing functions as remote terminal connection. In addition the optical line terminating module adopted for the DSU and OCU components is extreniely cost effective: e. g. its circuit adjustment has become easier by enlarging the emission peak wavelength range and optimizing module optical output. Consequently these technologies will facilitate the early and widespread installation of primaryrate interface services.