Managing lines, Fxs voice subscriber line, Fxo voice subscriber line – H3C Technologies H3C MSR 50 User Manual
Page 742: E&m subscriber line, E&m introduction, E&m start mode
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Managing lines
This section provides information on managing and configuring various types of subscriber lines.
FXS voice subscriber line
A foreign exchange station (FXS) interface uses a standard RJ-11 connector and a telephone cable to
directly connect with an ordinary telephone or a fax machine. An FXS interface accomplishes signaling
exchange based on the level changes on the Tip/Ring line and provides ring, voltage, and dial tone.
FXO voice subscriber line
A foreign exchange office (FXO) interface uses a RJ-11 connector and a telephone cable to connect local
calls to a PSTN or PBX. Like an FXS interface, an FXO interface accomplishes signaling exchange based
on the level changes on the Tip/Ring line. An FXO interface can be connected only to an FXS interface.
E&M subscriber line
E&M introduction
An E&M interface uses a RJ-48 telephone cable to connect a PBX. The PBX sends signals on the M (M
represents mouth) line and receives signals on the E (E represents ear) line. The voice router receives M
signals from the PBX and sends E signals to the PBX. An E&M interface can only be connected to another
E&M interface.
When E&M is applied in voice communication, two or four voice wires can be used. Besides, there are
two or four signaling wires. Therefore, 4-wire analog E&M actually has six wires at least. The 2-wire
mode provides full duplex voice transmission and voice is transmitted in two directions on the two wires.
The 4-wire mode is equivalent to the simplex mode and every two wires are responsible for the voice
transmission in one direction.
E&M start mode
An E&M interface supports E&M signaling and divides each voice connection into trunk circuit side and
signaling unit side (similar to DCE and DTE).
An E&M interface provides on-hook/off-hook signals and minimizes the interference. Because an E&M
interface does not provide any dial tone, one of the following three signaling technologies is used to start
dialing:
•
Immediate start—In this mode, the caller picks up the phone, and after a brief period, the dialed
number is sent to the called side. During this period, whether the called side has been ready to
receive the called number is not checked. After the called information is received, the callee can
pick up the phone to answer the call.