572 Chapter 8: WAN Protocols and Design
Jargon definitely confuses the issue with home ISDN services. Figure 8-23 outlines the
problem.
Table 8-28
Definitions for Function Groups in Figure 8-22
Function Group
Acronym Stands for
Description
TE1
Terminal Equipment 1
ISDN-capable four-wire cable. Understands
signaling, 2B+D. Uses S reference point.
TE2
Terminal Equipment 2
Equipment that does not understand ISDN
protocols and specifications (no ISDN
awareness). Uses R reference point, typically
an RS-232 or V.35 cable, to connect to a TA.
TA
Terminal adapter
Equipment that uses R and S reference points.
Can be thought of as the TE1 function group on
behalf of a TE2.
NT1
Network Termination
Type 1
CPE equipment in North America. Connects
with U reference point (two-wire) to telco.
Connects with T or S reference points to other
customer premise equipment.
NT2
Network Termination
Type 2
Equipment that uses a T reference point to the
telco outside North America, or to an NT1
inside North America. Uses an S reference
point to connect to other customer premise
equipment.
NT1/NT2
A combined NT1 and NT2 in the same device.
This is relatively common in North America.
Table 8-29
Definitions for Reference Points in Figure 8-22
Reference Point
Connection Between
R
TE2 and TA.
S
TE1 or TA and NT2.
T
NT2 and NT1.
U
NT1 and telco.
S/T
TE1 or TA, connected to an NT1, when no NT2 is used. Alternately, the
connection from a TE1 or TA to a combined NT1/NT2.
ch08.fm Page 572 Monday, March 20, 2000 5:17 PM