EMC and COMSEC problems on ISDN subscriber lines

ISDN signals conforming to CCITT recommendations can give rise to electromagnetic compatibility (EMC) problems if they are transmitted via unshielded lines. Investigations concentrating on common-mode interference signals as well as the construction of ISDN equipment that can cope with EMC are described. The issue of communication security (COMSEC) is examined, since these signals could be received by special equipment and the original information recovered. It is also possible to influence an ISDN transmission by means of external signals. It is shown that, by using shielded cables in the inhouse area and by adequate construction of the equipment, these problems can be virtually eliminated