E&M stands for a lot of Acronym like
- Ear an Mouth
- Earth and Magneto
- Receive and Transmit
E&m uses an RJ48 interface and is often used to provide tie-line connectivity to PBX. there are 5 types of E&M Interfaces ( I, II , III , IV, V) which are all supported by Cisco except the Type IV.
On this line , we can find the following signaling :
- Wink-start
- delay -start
- immediate-start
- tone-start
Need to more explanations about the different modes !
FXS is an RJ11 interface which is connecting a phone, a fax,… In contrast with FXO, FXS provides dial tone and ring voltage.
FXS can use also the same signaling ( loop-start and ground-start) but loop-start signaling is preferred on FXS line.
FXO is an RJ11 interface which is providing a connection to a PSTN Central Office (CO) or to a PBX interface.
A FXO is considered as a telephony line. We can then find 2 types of signaling :
- Loop-start signaling : this is a type of supervisory signaling that allows indication of on-hook and off-hook states. But this signaling is vulnerable to a condition knows as glare that involves 2 endpoints seizing a trunk a the same time.
- Ground-start signaling : Same as loop-start signaling but this time we suppress the glare effect on these lines.