thinQmaster Virtual testing partner Adaptive practice exams that find your weak spots and drill them. Every answer explained. From $69
Enroll

thinQmaster

Find your exam

Five questions free, before you decide.

Step 1 · choose a vendor

In one of our camps? Your practice exams come with the tuition — they are on your study page already.

Collaboration, Voice & AV · Intermediate

Ear and Mouth Interface (E&M)

An analog trunk interface, also called Receive and Transmit, used to tie PBXs together with separate signaling leads.

Definition

E&M interfaces carry voice on two or four wires plus separate E (ear, receive) and M (mouth, transmit) signaling leads. Five signaling types (I through V) define how the leads are powered and grounded, and Type V is common outside North America. E&M supports wink-start, immediate-start and delay-dial start signaling and is largely replaced by digital T1/E1 and SIP trunks.

Example

A legacy tie-line between two PBXs uses an E&M Type V interface on each voice gateway.

Exam tip

Recognize E&M as a PBX-to-PBX trunk type, unlike FXS (phones) and FXO (CO lines).

Related terms