Carrier Grade GroomerII – Installation Guide
1.7.2 75 Ohm E1 trunk connection
NOTE
Each E1 trunk in a GroomerII chassis has configurable impedance.
Some legacy E1 PSTN networks require 75 Ohm trunk connection. The default
impedance for E1 trunks in the GroomerII is 120 Ohm. It is important to confirm with
the network operator which impedance the PSTN is using during the installation
process, as a mismatch can lead to signal degradation and erratic equipment
behaviour that is difficult to diagnose later.
The following signalling services may be expected to be configured for 75 Ohm in
legacy switching equipment which provide the following protocols:
•
DASS2
•
DPNSS
•
SS7/ISUP
•
All E1 CAS protocols
Each 75 Ohm trunk is normally connected via a pair of coaxial cables with BNC
connectors. A Balun is available to convert between RJ45 and co-axial cabling. The
Balun also converts between 120 and 75 Ohm interfaces, so the system does not
need to be configured for 75 Ohm operation when this type of converter is used.
Figure 1-4 75 Ohm E1 Balun
14 of 44
