User`s guide

ADSL/VoIP Gateway User’s Guide
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The product provides Internet access using DSL for the LAN
and Wireless LAN computers. The phones connected to the
Voice-IAD system are standard analog phones that are identical
to the other telephones connected to the Home telephone
wiring system. The phones can use DTMF or Pulse dialling to
make either PSTN or VoIP calls. The Voice-IAD system will
route or receive calls over PSTN or VoIP depending on the
dialed telephone number or the way in which an incoming call is
received. In cases where the VoIP call agent cannot be
reached, the DSL line is down or there is no power - calls will
always be routed to the PSTN via a Failsafe relay (hence the
phones will be electrically connected to the PSTN). QoS
(Quality of Service) is also used to ensure voice calls are placed
at a higher priority than data traffic routed between the
LAN/WLAN and DSL interface.
Voice Terminology
Before beginning an overview ,several Voice and telephony
terms must be understood.
FXS
Telephones, fax machines, and modems are examples of
telephony devices. These devices typically connect (via
telephone lines) to RJ11-jack Foreign Exchange Station (FXS)
interfaces on telephony hardware. The FXS interface provides
battery, signaling and an audio connection for the devices.
FXO
An FXO interface is the Foreign Exchange Office interface
which connects to a PSTN Exchange.
Codec
Audio data from the FXS port or FXO port is sampled via an
analog-to-digital converter, and audio data to the FXS port is
generated via a digital-to-analog converter. These functions are
integrated into a single circuit, the codec (short for coder-
decoder, since typically, codecs encode/decode audio samples
using 8-bit or 16-bit PCM encoding). Codec integrated circuits
may handle bidirectional audio data on single or multiple FXS
ports, or FXO ports. The codec produces a constant stream of
audio data in a Time Division Multiplexed (TDM) fashion, which
places the audio data from each port into time slots. The TDM
transmission is synchronized into ‘frames’ of audio data by
aligning with the codec's ‘frame sync’ signal. An FXS port's time
slot is referred to as an ‘audio channel.’
In a typical VoIP system the Codec is a separate chip but it is
more accurate to view the codec as an integral component of
the overall integrated circuit functionality.
Voice features
The main Voice features supported in the Voice software
release are listed below: