Switching to VoIP

This is the Title of the Book, eMatter Edition

Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

Point-to-Point Trunking

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When privately owned cable can’t be run between locations due to excessive dis-

tance, telco-owned facilities, like T1s, T3s, or wireless solutions can be used for pri-

vate trunking. BRI-ISDN is often used for low-density switch-to-switch trunking

across relatively short distances, but its high cost is a discouraging factor. BRI-ISDN

allows two voice calls to be carried at once.

T1 circuits are far more abundant than BRI-ISDN in trunking situations, because

they offer 12 times the capacity. Even though the cabling used to carry the T1 circuit

is the phone company’s property, and the phone company charges a fee for the use

of that pathway, the T1 circuit used to connect two switches can still be called a pri-

vate trunk because the voice calls it carries are not considered PSTN traffic.

The ITU’s recommendation for T1 technology describes both the transport and data

link layers. The physical layer for a T1 circuit tends to be two pairs of copper wiring.

The phone company may connect the T1 through its local access transport areas

(LATAs) using fiber, but the part of the circuit that connects to the customers’ loca-

tions is almost always copper.

Even higher-density T1-like circuits are available for private trunking if the need

exists. DS3 circuits multiplex ...