Monday, March 31, 2014

Telephone Trunks for Call Centers

By: John Shepler

All businesses need telephone lines of some sort. Independent professionals may rely on a smartphone for wireless communication, but businesses with offices or stores open to the public or with two or more employees almost always have some sort of landline installed. Let’s take a look at the analog and digital options available and the advantage of installing telephone trunk lines to increase capacity and reduce cost.

Plain Old Analog
Analog phone lines are the legacy technology of the phone companies going back over a century. You’ll hear them described as POTS or Plain Old Telephone Service. POTS lines are well established, highly reliable and engineered for high voice quality on both local and toll calls. Standard phones, including desk sets and cordless phones with multiple handsets, are analog phones and plug directly into analog business phone lines.

Broadband Phone
The digital solution for a single phone line is a broadband Internet connection shared with the computers. This option is usually chosen for its low cost, but voice quality can degrade and certain applications, like FAX machines and alarm systems, may not function correctly.

Adding More Lines
What about the vast majority of businesses with more than one phone line, especially those with an in-house contact center or specializing as a call center? Small operations sill rely on analog phone lines. You can add analog lines one at a time and plug them into your key telephone system or PBX switching system. Each outside line has its own phone number.

How Costs Add Up
Adding analog phone lines incrementally as you need them works well until you get more than half a dozen to a dozen separate lines. There are no technical issues, but costs mount up. Two lines cost twice as much as one line. Six lines cost six times as much. There is no economy of scale as these are independent lines.

How Trunking Saves
The strategy for reducing costs while maintaining voice quality and reliability is called trunking. Trunking simply means combining multiple lines to create a single trunk line with the same capacity. Trunking was invented by the telephone industry to transport dozens or even thousands of phone conversations efficiently from switching office to switching office. Originally, this was done with analog technology called carrier telephony. In recent decades, it’s all gone digital from office to office, leaving analog POTS lines only for that last mile connection between the telco office and the customer’s premises.

T1 Telephone Trunks
The first digital trunk line that was introduced by the phone industry for business users was the T1 telephone line. Yes, this is the same T1 technology that you may be using for point to point or dedicated Internet access. The difference is that the T1 line is divided or “channelized” into 24 separate segments or time slots. Each channel can transport one two-way telephone conversation and is the equivalent of an analog POTS line. You can use an appliance called a channel bank to convert between analog phone and the T1 line. Most in-house PBX phone systems have the necessary interface to do this or it can be added easily with a plug-in card.

Cost Advantage of T1
The big advantage of T1 trunks is that they become cost competitive with multiple POTS lines when you get over 6 to 10 outside lines. If you need more than a dozen phone lines for your desks or a call center operation, T1 is the lower cost option. Multiple T1 lines can be added to provide blocks of 24 outside lines incrementally.

ISDN PRI Improves on T1
A newer version of the T1 line is called ISDN PRI or Primary Rate interface. It uses the same T1 line but reserves one channel for signaling and switching. The other 23 channels are available as separate phone lines. ISDN PRI is popular with call centers because it provides faster call setup and teardown than the older T1 telephone lines. It also offers digital data ,such as Caller ID, that is not generally available on just T1 trunks. Like T1, though, multiple ISDN PRI trunks can be installed to provide as many outside lines as needed. Cost is competitive with T1 and most PBX systems come with the PRI interface already installed.

SIP Trunking, The Emerging Standard
While ISDN PRI is now the standard in commercial telephone trunking technology, an even newer technology is available to better support enterprise VoIP telephone systems. This is called SIP trunking. SIP is the switching protocol used by IP telephones and VoIP phone systems.

SIP vs T1
SIP trunks are also digital, but differ from T1 lines in that they are based on packet switching rather than time division channelization. Packet switching is the heart of all Ethernet networks that support computing. What companies are doing is replacing their old analog telephones with IP phones that connect to the same network as the computers. SIP trunks extend this connection out to the service provider for multiple telephone lines or a combination of voice and data.

Private Lines vs The Internet
Note that high performance SIP trunks are private lines between the user and the carrier and do not suffer from the vagaries of Internet broadband phone. SIP trunks often have the ability to also supply Internet service, but the telephone packets have priority to maintain high voice quality. SIP trunking is becoming popular for call center operations as companies replace their old PBX systems with newer IP PBX systems or choose to outsource the switching function to the cloud.

How to Choose
Which type of telephone trunking arrangement is optimum for your organization? Get some expert advice on the tradeoffs and competitive pricing from multiple carriers serving your location. Call now toll free (888) 848-8749 or enter your inquiry at

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