> This subject is somewhat timely for a project I'm dealing with now; an ISDN > S/T and U > interface tester. The S/T port for end-user access is well defined. However, > based > on the feedback I get from our designers, the U interface has no firm > electrical > spec, making it hard to determine with certainty the isolation/insulation > requirements.
I have said this before and have to repeat it, THERE IS NO SUCH THING AS AN R, S, T OR U INTERFACE IN ISDN. THERE ARE R, S, T OR U REFERENCE POINTS. THOSE ARE NOT PHYSICAL INTERFACES NECESSARILLY. The U-reference point is present in all ISDN configurations. The difference is that in the USA, the network terminating point is at the U-reference point and in Europe, the network terminating point is at the S or T reference point. Therefore, there is no great reason in Europe to wax eloquent about the U-reference point, whereas there is in the USA. Ciao, Vic
