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Trunk Phone Lines: An Introduction



25 Apr 2017

Business is closely tied to the telecommunications industry. There have been countless advances that have changed the way businesses operate. The phone book and yellow pages changed the way we found services in our area. Conference calls changed the way business meetings could be held. Trunk line systems made call centers possible and revolutionized customer service.Trunk Phone Lines: An Introduction


What Is a Trunk Line and What Is "Trunking"?

To understand what a trunk line is, you must first understand what a trunk is. A trunk is a single communication between two access points. The points in the exchange are identified as a switching center, the start point, and the node, the end point. A trunk makes it possible for any type of digital communication to occur between these two points.

Trunk lines are circuits that bridge telephone switchboards they are different from standard local loop circuit. Their name “trunk” comes from how trunk line systems work. Imagine a tree trunk with many branches coming out of it. Trunk line systems are typically used in telecommunication systems that are very high frequency. Large corporations use “trunking” to connect everyone within their network.

If you’ve dialed a number and then an extension you’ve dialed a trunk line system. Rather than having many different phone numbers an organization will have one main line and then many different lines that you can be connected to by dialing an extension. These networks within networks are known as Private Branch Exchange (PBX) systems, they connect the internal communications of a business.

The act of “trunking” reduces the size of a network while increasing bandwidth, meaning that the connection and data transfer is both better quality and quicker. Today, data can be transmitted in many different forms through trunking.

What Is Primary Rate Interface (PRI) Trunking?

Seen as the original version of trunking, Primary Rate Interface (PRI) trunking is used by businesses to connect their employees’ calls within an organization. It is considered the older version of trunking due to its limit on simultaneous calls. A business using PRI trunking will only be able to have 23 phone conversations at once per trunk as PRI lines only have 23 voice channels to use.

PRI trunking is divided into two different types of trunks. E1 trunks are mainly used in Europe while T1 is mainly used in the United States, Canada, Hong Kong, and Japan. PRI trunking is no longer popular since it doesn’t allow internet services such as call screening or third-party application usage.

What Is Session Initiation Protocol (SIP) or VoIP Trunking?

Session Initiation Protocol (SIP) trunking utilizes VoIP. SIP is the modern day version of trunking since it allows businesses to transfer data including video, desktop sharing, and web conferencing, in addition to voice.

SIP trunking is low cost compared to PRI trunking and much more dynamic due to the various services it offers.

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