IP/Network

Trunk

What is Trunk ?

According to WhatIs.com, it is defined as follows : (Refer to here for the original page)

A trunk is a physical path or link in a communications system that is designed to handle many transmissions simultaneously and that interconnects major switching centers or nodes. Depending on the system, a trunk may carry transmissions in analog or digital form. Transmission content may include voice (as in the conventional telephone system), text, computer programs, images, video or control signals..

According to Techopedia, Trunk is defined as follows : (Refer to here for the original page)

Trunking is a technique used in data communications transmission systems to provide many users with access to a network by sharing multiple lines or frequencies

Trunking can also be defined as a network that handles multiple signals simultaneously. The data transmitted through trunking can be audio, video, controlling signals or images.

If you already know what Trunk is, you would understand the exact meaning of these definitions and think both of these definitions are well described. But if you are new to Trunk/Trunking concept and just started studing on this, these formal definition would not give you much understanding. This is one of the biggest difficulties whenever you are trying to learn a new technology. When you need a dictionary, the dictionary would not make much sense to you. When the dictionary make sense to you, you don't need the dictionary anymore because you already knows about it :)

I don't know who used the term 'Trunk' in communication, but it is highly likely that he/she has thought of the tree structure as shown below. Trunk is the part marked below. As you see, the trunk is the part all the branches are merged together.. or the part from which all the branches split out. Just take this image in your mind.

As far as I heard, the term Trunk is first used in wired telephone communication system. Think of a situation where you have to build a telephone network between the two cities. There are many telephones installed in each of the city and each of the phone has its own dedicated line. Now the questions is how to build the lines connecting the two cities. Probably the best option for each phone subscribe is to install the dedicated inter-city lines, but as you easily see the cost would be the biggest issue. So they invented a method to combine or share the many telephone lines into a single (or only a few) inter-city connection lines. This special line merging many of the terminal telephone lines was called 'Trunk' lines.

As IP based communication emerges, we had the same problem as in telephone system construction and they used the similar method of sharing/combining the multiple IP traffic into single (or a few) special lines and this line is called IP Trunk.

Now go back to the top of this page and read the formal definition again. I hope it would make more sense to you now.