Lines vs Trunks

Switched Access trunks form the communications path between switches and switching offices, and lines connect end users (typically residential and small business) to End Offices. Both carry voice traffic. Another key difference is that lines are dialable and trunks are not. This means that lines have a phone number, while trunks do not. 

With the exception of Feature Group A (which uses a line connection on both sides of End Offices - a rarity), voice traffic is always carried on trunks to End Offices where it is switched to lines which carry the traffic to and from an end user's location. 

Lines - only support pulse tones or touch tone (known as DTMF Address Signaling). These are the same types of signals generated by a rotary dial or touch tone telephone. Since FG A is the only Feature Group that uses a lineside connection, it is the only Feature Group that supports dial pulse address signaling.

Trunks - support multifrequency, also known as MF Address Signaling. MF is similar to DTMF, but consists of different tones that are only used between switches. DTMF and MF are up to ten times faster than dial pulse. Trunks also support an even faster method of Address Signaling known as Signaling System 7 (SS7), which is carried "out-of-band". This high speed, digital address signaling method significantly shortens the amount of time required to complete a call compared with DTMF or MF.