A FQDN consists of a host and domain name, including
FXO
Foreign eXchange Office
An FXO device can be an analog phone, answering machine, fax, or anything that handles a call from the telephone company like AT&T. They should also operate the same way when connected to an FXS interface.
An FXO interface will accept calls from FXS or PSTN interfaces. All countries and regions have their own standards.
FXO is complimentary to FXS (and the PSTN).
FXS
Foreign eXchange Station
An FXS device has hardware to generate the ring signal to the FXO extension (usually an analog phone).
An FXS device will allow any FXO device to operate as if it were connected to the phone company. This makes your PBX the POTS+PSTN for the phone.
The FXS Interface connects to FXO devices (by an FXO interface, of course).
DHCP
The Dynamic Host Configuration Protocol (DHCP) is an Internet protocol for automating the configuration of computers that use TCP/IP. DHCP can be used to automatically assign IP addresses, to deliver TCP/IP stack configuration parameters such as the subnet mask and default router, and to provide other configuration information such as the addresses for printer, time and news servers.
ECHO CANCELLATION
Echo Cancellation is used in telephony to describe the process of removing echo from a voice communication in order to improve voice quality on a telephone call. In addition to improving quality, this process improves bandwidth savings achieved through silence suppression by preventing echo from traveling across a network.
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