Trunking is a rather broad term used to refer to the act of sharing a certain type of communication system by many different users. Essentially, it refers to the use of a certain number of communication pathways by a number of users greater than the number of pathways. Although trunking first came into use in telephone systems, it now is employed in Internet and radio communications systems as well. Many different types of trunking exist today, with a wide variety of applications.
Radio Trunking in General
The most common types of trunked radio systems in operation today are used by public safety organisations to coordinate their field operations. Most of these systems have one control channel which sends messages out, and many traffic channels, upon which messages can be sent back the central dispatch. Among the types of trunked radio systems are the Motorola Type I and Type II systems, the Enhanced Digital Access Communication System (EDACS), and Logic Trunked Radio (LTR) systems.
Motorola Trunking Systems
Motorola systems are the most common trunked radio systems, especially in public safety organisations. Type I systems don't have digital capability, while some Type II systems do. In addition, Type II systems are generally newer and capable of doing more than Type I systems.
EDACS Trunking Systems
EDACS systems are attractive because they can carry both analogue and digital voice formats, and can also be encrypted, that is, people with scanners can have their access to the system blocked.
LTR Trunking Systems
LTR systems are not used very often in public safety, but frequently in business and industrial settings. These systems do not have a control channel.
Trunking is not just used on radio frequencies, however. In computing, the term trunking is also used to refer to a type of link between devices operating upon a virtual local area network, or VLAN. These devices can be a switch, a router, or an end station; the trunking allows these devices to interact with one another without having to be exclusively connected to one VLAN. Three major types of VLAN trunking exist: trunking between two switches, trunking between a switch and a workstation or router, and trunking between a switch and an end station or router.