9.1 Trunking  
  9.1.1 History of trunking  
The history of trunking goes back to the origins of radio and telephony technologies. In radio technologies, a trunk is a single communications line that carries multiple channels of radio signals.

In the telephony industry, the trunking concept is associated with the telephone communication path or channel between two points. One of these two points is usually the Central Office (CO). Shared trunks may also be created for redundancy between COs.

The concept that had been used by the telephone and radio industries was then adopted for data communications. An example of this in a communications network is a backbone link between an MDF and an IDF. A backbone is composed of a number of trunks.

At present, the same principle of trunking is applied to network switching technologies. A trunk is a physical and logical connection between two switches across which network traffic travels.