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ISDN Protocols and Design 571
Figure 8-22
ISDN Function Groups and Reference Points
Router A was ordered with an ISDN BRI U reference point, referring to the I.430 reference
point defining the interface between the customer premise and the telco in North America.
Router B was bought with an ISDN BRI S/T interface, implying that it must be cabled to a
function group NT1 device in North America. An NT1 function group device must be
connected to the telco line through a U reference point in North America; the S/T interface
defines the connection to Router B. Router B is called a TE1 (Terminal Equipment 1) function
group device. Finally, non-ISDN equipment is called a TE2 (Terminal Equipment 2) device and
is attached using the R reference point to a terminal adapter (TA) function group device.
Alternately, a TE1 can connect using an S reference point to an NT2 function group, as shown
in case D of Figure 8-15.
Table 8-27 summarizes the types from Figure 8-22. Table 8-28 and Table 8-29 provide a
summary of formal definitions.
Table 8-27
Figure 8-22 Function Groups and Reference Point Summary
Router
Function Group(s)
Connected to Reference
Point(s)
A
TE1, NT1
U
B
TE1
S/T (combined S and T)
C
TE2
R
D
TE1
S
A
U
B
NT1
S/T
U
C
D
TA
NT1
R
S/T
U
NT2
NT1
S
T
U
Telco
ch08.fm Page 571 Monday, March 20, 2000 5:17 PM