CCNA Complete Guide 2nd Edition.pdf - Cisco Learning Home

- TE is referred to as Terminal Equipment / Endpoint.
TA is referred to as Terminal Adapter.
NT is referred to as Network Termination.
- Below lists the ISDN reference points (demarcations):
Reference Point Connects Between
R TE2 and TA (a non-ISDN device and a TA). TE2s and TAs are regular.
S TE1 and NT1 or NT2, or TA and NT1. TE1s are special.
T NT1 and NT2.
U NT1 and Telco.
S/T NT1 and TE1 or TA (when NT2 is not being used) or
TE1 and a combined NT1/NT2 (when NT2 is being used).
- U = U.S. demarcation. S, T, S/T = Non-U.S. demarcation.
Figure 26-5: ISDN Home User and Reference Points
- By looking at the back of a Cisco router, one may evaluate its ISDN connection ability.
BRI The router has an ISDN BRI. It is a TE1 as a native ISDN interface has already built-in.
U The router has a built-in NT1.
else an existing serial interface will be used to connect it to a TA to provide BRI connectivity.
- Q: What will happen if we connect a router with a U interface to an NT1?
A: This will damage the router interface, as the router U interface already has a built-in NT1.
- ITU defines the mentioned ISDN access options for BRI, as it was targeted at consumer market;
whereas PRI was targeted at corporate customers, due to its larger number of B channels (larger
bandwidth). ITU did not define function groups and reference points for ISDN PRI. PRI wiring
is not multipoint; there is only a straight connection between a CSU/DSU and a PRI interface.
Note: BRI wiring (or configuration) supports multipoint, where there are 2 phone numbers, one
for each B channel. With multipoint configuration, 2 devices may share a BRI line, and a phone
number (in fact, Service Profile Identifier, SPID) will be assigned for each device.
PRI-U
RS-232
(Serial)
(R)
PRI CSU
ISDN
Modem
TA & NT1
CSU
Figure 26-6: ISDN PRI Connections
191
(U)
Service Provider Network
Service Provider
Network
Copyright © 2008 Yap Chin Hoong
yapchinhoong@hotmail.com