:"This is about the network-design strategies; for riding in auto cargo space, see
Trunking (auto), and for the UK term for electrical wireways, see Electrical conduit#Trunking."
Trunking is a concept in modern communications by which a communications system can provide network access to many clients by sharing a set of lines or frequencies instead of providing them individually. This is analogous to the structure of a tree with one trunk and many branches. Examples of this include telephone systems and the VHF radios commonly used by police agencies. More recently
port trunkinghas been applied in computer networking as well.
How the term came to apply to communications is unclear, but it probably derives from transport. In the middle 19th century the principal road of India was named
Grand Trunk Road. The Grand Trunk Railwayin Canada was named in 1852, long before any telephone cable. Since telephone trunks, trunk railways, and trunk roads connect branch offices or branch roads, they act much like the trunk of a tree.
An alternative explanation is that, from an early stage in the development of telephony, the need was found for thick cables (up to around 10 cm diameter) containing many pairs of wires. These were usually covered in lead. Thus, both in colour and size they resembled an
elephant's trunk. This leaves open the question of what term was applied to connections among exchanges during the years when only open wire was used.
In radio communication (public safety, etc.), trunking refers to the ability of a signal to hop frequencies. Initially, all communication is received at known frequencies, but as silence is detected the site controller will broadcast new frequencies on which to communicate via a control channel, and the entire group of listening units will simultaneously migrate to that next frequency. [http://www.tech-faq.com/trunking.shtml (aeolianmeson)] [http://www.police-scanner.info/scanning/trunked-radio-systems.htm (aeolianmeson)]
telecommunications, a trunk is one of [From the Federal Standard 1037Cand from MIL-STD-188and from the Code of Federal Regulations, TelecommunicationsParts 0-199] :
* In a
communications network, a single transmission channel between two points, which are the switching centers or nodes or both. See Trunked radio system.
* A circuit between
telephone switchboards or other switching equipment, as distinguished from local loopcircuits which extend from telephone exchangeswitching equipment to individual telephonesor information origination/termination equipment.
When dealing with a PBX, trunk lines are the phone lines coming into the PBX from the telephone provider [Versadial, [http://www.versadial.com/call_recording_terms.html#trunk Call recording encyclopedia] , last accessed 18 Apr 2007] . This differentiates these incoming lines from extension lines that connect the PBX to (usually) individual phone sets. Trunking saves cost, because there are usually fewer trunk lines than extension lines, since it is unusual in most offices to have all extension lines in use for external calls at once. Trunk lines transmit voice and data in formats such as analog, T1, E1,
ISDNor PRI. [http://www.versadial.com/call_recording_terms.html#trunk See illustration here] The dial tonelines for outgoing calls are called DDCO (Direct Dial Central Office) trunks.
In the UK and the Commonwealth countries, a "trunk call" was a
long distanceone as opposed to a " local call". See Subscriber trunk diallingand Trunk vs Toll.
Trunking also refers to the connection of
switches and circuits within a telephone exchange. [Flood, J.E., "Telecommunications Switching, Traffic and Networks" Chapter 4: Telecommunications Traffic. New York: Prentice-Hall, 1998.] Trunking is closely related to the concept of Grading. Trunking allows a group of inletswitches at the same time. Thus the service providercan provide a lesser number of circuits than might otherwise be required, allowing many users to "share" a smaller number of connections and achieve capacity savings. [ Motorola, [http://www.motorola.com/LMPS/RNSG/trunking Trunking Communications Overview] , last accessed 13 February 2005.] [The Genesis Group, [http://www.genesisworld.com/trunking.asp Trunking Basics] , last accessed 13 February 2005.]
computer networking, trunking refers to the use of multiple network cables or ports in parallel to increase the link speed beyond the limits of any one single cable or port. This is called port trunkingor link aggregation. Trunks may be used to interconnect switches, such as major, minor, public and private switches, to form networks.
In the context of VLANs, Cisco uses the term "trunking" to denote a network link carrying multiple VLANs between 2 switches or between a switch and a router, through the use of a "trunking protocol." To allow for multiple VLANs on one link, frames from individual VLANs must be identified. The most common and preferred method, IEEE 802.1Q adds a tag to the
Ethernet frameheader, labeling it as belonging to a certain VLAN; Since 802.1Q is a non-proprietary standard, it is the only option in an environment with multiple vendor equipment. Cisco also has a proprietary trunking protocol called Inter Switch Link which encapsulates the Ethernet frame with its own container, which labels the frame as belonging to a specific VLAN.
Multi-Link Trunking (MLT): Nortel's Port Aggregation Protocol
Split multi-link trunking( SMLT): Nortel's proprietary enhancement to LACP
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