Analog Articulation Ports
Analog articulation anchorage interfaces affix routers in packet-based networks to analog twowire
or four-wire circuits in telephony networks. Two-wire circuits affix to analog telephone
or fax devices, and four-wire circuits affix to PBXs. Access to the PSTN
CO are about fabricated with agenda interfaces. Three types of analog articulation interfaces are
supported by Cisco gateways, as illustrated in Figure 3-9.
The afterward is a abundant account of anniversary of the three types of analog voice
interfaces:
■ FXS: An FXS interface connects the router or admission server to end-user equipment
such as telephones, fax machines, or modems. The FXS interface food ring, voltage,
and punch accent to the base and includes an RJ-11 adapter for basal telephone
equipment, key sets, and PBXs.
Figure 3-9 Analog Articulation Ports
■ FXO: An FXO interface is acclimated for trunk, or tie-line, access to a PSTN CO or
to a PBX that does not abutment E&M signaling (when the bounded telecommunications
authority permits). This interface is of amount for off-premises base applications. A
standard RJ-11 modular blast cable connects the FXO articulation interface agenda to
the PSTN or PBX through a blast bank outlet.
■ E&M: Block circuits affix blast switches to one another. They do not connect
end-user accessories to the network. The best accepted anatomy of analog trunk
circuit is the E&M interface, which uses appropriate signaling paths that are separate
from the block audio aisle to aback advice about the calls. The signaling paths
are accepted as the E-lead and the M-lead. E&M access from routers to telephone
switches or to PBXs are bigger to FXS and FXO access because
E&M provides bigger acknowledgment and abstract supervision.
The name E&M is anticipation to acquire from the byword Ear and Mouth or rEceive and
transMit, although it could additionally appear from Earth and Magneto. The history of these
names dates aback to the aboriginal canicule of telephony, aback the CO ancillary had a key that
grounded the E circuit, and the added ancillary had a sounder with an electromagnet
attached to a battery. Descriptions such as Ear and Mouth were adopted to advice field
personnel compassionate and actuate the administration of a arresting in a wire.
Like a consecutive port, an E&M interface has a DTE/DCE blazon of reference. In the
telecommunications world, the trunking ancillary is agnate to the DCE and is usually
associated with CO functionality. The router acts as this ancillary of the interface. The
other ancillary is referred to as the signaling side, like a DTE, and is usually a accessory such
as a PBX.
134 Authorized Self-Study Guide: Cisco Articulation over IP (CVOICE)
V V
FXS V
WAN/PSTN
FXO V
E&M
E&M
– Best accepted anatomy of analog block circuit
E&M
FXO
PSTN
FXO
– Acclimated for trunk, or tie line, access to a PSTN CO or to a PBX that does not
support E&M signaling
FXS
– Connects anon to end-user accessories such as telephones, fax machines, or modems
Note Depending on how the router is affiliated to the PSTN, the articulation aperture might
provide clocking to an absorbed key arrangement or PBX, because the PSTN has added accurate
clocks, and the articulation aperture can canyon this adequacy to after devices.