Trunk Groups

Trunks connect switches and switching offices. 

Terminology - the term "Trunk" sounds big - after all, we think of a tree trunk, or perhaps a huge bundle of wires as a trunk.  In fact, many times, we will refer to a trunk as a T1 and OC3's that connect offices as "Intermachine Trunks" or IMT's. 

*** however, in terms of voice, one voice circuit requires a DS0 - and that is the bandwidth of one voice "trunk" - DS0.  From here on, we will refer to a trunk as one DS0 !!!

A single trunk is a DS0 can carry only one phone call at any given time, which is comparable to a single seat on a vehicle such as a shuttle bus. The more seats available, the less likely a passenger will have to wait for a ride to or from the airport. Likewise, the more trunks an Interexchange Carrier orders, the less likely end users will hear an "all circuits are busy" message when they try to dial long distance. Consequently, Interexchange Carriers typically order multiple trunks within a trunk group.

A DS0 facility is basically the size and capacity of a single trunk. It is most commonly used for, but not limited to, a particular
type of Switched Access Service called Feature Group A.

A DS1, sometimes referred to as a T1, has a defined signal rate or speed of 1.544 megabits per second, which enables it to
hold up to 24 trunks. A trunk takes up 64 kilobits per second.

A DS3, sometimes referred to a T3, has a defined signal rate of more than 44.7 megabits per second. Consequently, it has the
capacity to hold up to 28 DS1s or 672 trunks.