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5-4 ELECTRONIC TANDEM NETWORK (ETN) THROUGH THE ETN AND PNA PACKAGES
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Access and Bypass Access Tie Trunks
An access tie trunk is a 1-way outgoing or 2-way trunk connecting a main to a tandem switch. A bypass
access tie trunk is a 1-way outgoing trunk connecting a tandem switch to a main, satellite, or tributary that
is homed on another tandem switch. (Refer to figure 5-1.) Bypass access tie trunks are used when:
• A main switch receives a high volume of calls from a distant tandem switch, and/or
• It is more economical to route the calls over a separate bypass access tie trunk than through the tandem
switch to which the main is homed.
CHICAGO
DIMENSION 2000
NEW YORK CITY
SYSTEM 85
FINAL
FINAL FINAL
INTERMEDIATE
HIGH
OVERFLOW
OVERFLOW
LOS ANGELES
SYSTEM 85
ATLANTA
DIMENSION 2000
OVERFLOW
USAGE
PRIMARY HIGH USAGE
Figure 5-2. An Example of Intermachine Tie Trunk Usage (Overflow Routing)