Concepts and Principles of Operation
6
Physical Interface
The ISDN physical interface is a available in two types, U and S/T. The S/T interface relies on a external
device called NT1 to connect the user equipment to the ISDN line. The S/T interface is used in most parts
of the world. The U interface, widely used in North America, is designed for user equipment with built-in
NT1. The NT1 (also called ISDN DSU) built-in ISDN device is also allowed In Japan. The Japanese U
interface however works differently from the rest of the world.
ISDN Switch Variants
When your Hypertec Router is delivered, it is preset to use a default ISDN variant. The ISDN variant is
the type of ISDN operation run by your Telephone company.
Interface Type
National ISDN Variants
Default Setting
U
North American
National ISDN
S/T
Japan
NTT
S/T
Rest of the World
EURO-ISDN
You must have the right ISDN variant (switch) configured as provided by your ISDN service provider
or telephone company.
