Trunk Circuit Networks

What It Is

Used in the context of contact centers, a basic “trunk circuit” is a telephone line connecting the phones at the contact center to the telephone network. Each circuit can handle one phone call at a time. The number of circuits required depends on the number of simultaneous callers the contact center wishes to accommodate. For smaller contact centers, a special trunk circuit known as T–1 is commonly used to connect the contact center system to the telephone network. Each T–1 circuit can accommodate up to 24 simultaneous phone calls at a time. For example, if your contact center wishes to accommodate 36 simultaneous phone calls, you’ll need to put in 2 T–1s.

There are two flavors of T–1s:

• The “plain” T–1 can handle up to 24 simultaneous phone calls at a time. 
• The “PRI” (Primary Rate Interface) T–1 can handle 23 phone calls with one channel reserved for data. This data channel is used to convey caller and call status information for the 23 channels so that the calls are only sent to the contact center at the optimum time when resources are available to service the callers. For this reason, PRI circuits are commonly used for contact center installations. 

For very large contact center installations, a circuit known as T–3 may be used. Each T–3 can accommodate up to 28 T–1s.  

Why It's Important

Trunk circuits are the main arteries for a contact center. They carry calls to and from the contact center system and the telephone network to enable customers to transmit/receive information and services. T–1s and T–3s offer the ability to handle more calls simultaneously and can be a more cost effective solution when higher call volume handling capacity is required.

How To Implement

The primary factors that drive the decision to use individual trunk circuits, T–1, or T–3 are:

• The number of simultaneous phone calls the contact center wishes to accommodate.
• The relative costs of the individual trunk circuit, T–1 and T–3 circuits. 

Generally, the cost of a T–1 is less expensive than the cost of 24 individual trunk circuits, and the cost of a T–3, including the multiplexing equipment to break out the T–1s, is less expensive than the cost of 28 individual T–1s. Since the circuit costs are dependent on the geographic area the contact center is located, a cost analysis will need to be done on each contact center location to determine the lowest cost solution.

For federal agencies and certain entities who are authorized to obtain services from the General Services Administration (GSA), trunk circuits of various capacities can be obtained through the Networx contracts managed by GSA. Requests for services under the Networx contracts are generally handled by trained Authorized Agency Representatives (DARs) within the Telecommunications or Information Technology (IT) department of an agency. Consult the appropriate department within your agency for assistance in ordering telecommunications services under the Networx contracts.

Content Lead: Tonya Beres
Page Reviewed/Updated: April 23, 2012