To understand the difference in ISDN interfaces on an Ascend Pipeline 50/75/85 Router, you need to know: There are two different interfaces for the ISDN, the S and the U. The S interface is for our European market, where we use a NT (network terminator) box, converting from two copper wires to a 4 line so called S0 bus system. There we can run up to 8 devices, one Pipeline and 7 phones.

The U type is a two wire connection directly at the telco line. No other unit may be used in parallel with this one unit.

this is the S (4 wire) interface, for example P50 SBRI

	this is the U (2 wire) interface, for example P50 UBRI