Technical data

www.westermo.com Theoretical and general applications 99
Physical layer
Signalling between the telecommunications exchange’s line terminal (LT) and user’s
network terminal (NT) takes place over the U-interface while signalling at the user’s
premises, between NT and terminal adapter TA takes place over the S-interface. In the
U-interface frames with a 240 bits length are used, these are transferred at a rate of
160 kbit/s. The U-interface’s frames are structured as set out in the figure below.
TE1
TA
S/TUV
NT-1
TE1
TE2
R
Network Termination.
Used to convert U to S/T interface
Supplied in Europe by Telco
ISDN equipment that
can connect NOT
directly to ISDN line
Equipment at phone
company switch
Used to connect TE2
devices to ISDN line
U Interface
Termination point in USA
ISDN equipment
that can connect directly
to ISDN line
Standard PSTN equipment
has an R interface
S/T interface
Termination point in Europe
B A C K