| Unicoi
Voice (VoIP) Gateway PSTN Call Manager Module |
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The PSTN Call Manager
provides the link between the terminal adapter’s
dual POTS lines and remote VoIP devices. The PSTN Call
Manager’s state machine manages the entire call
sequence including, for example, the basic standard
use case of a telephone unit going off hook, dialing
a call, establishing a connection, sending and receiving
voice content, and ending the call when the telephone
is placed back on hook.
To provide a better user experience, voice prompts are
used in situations where a universal standard feedback
does not exist. For example, a voice prompt would not
be used for a busy signal, but if a connection to the
user’s VoIP proxy could not be established a voice
prompt would inform the user of the situation and provide
information on how to troubleshoot the situation.
When placing a call, the state machine processes the
DTMF digit detection events from the POTS line and upon
detecting the valid entry of a phone number it tries
to establish a connection (an advanced configuration
option allows the definition of what is valid; this
allows the unit to be used in an office setting where,
for example, a four-digit number starting with a ‘3’
is an inter-office call).
The PSTN Call Manager can establish connections to either
a VoIP proxy server or directly to another VoIP handset.
If a line is configured to use a proxy, a point-to-point
call can still be made by using the “speed dial”
option which is configured via the web-based configuration
tool.
Once a connection is successfully established, voice
data is streamed to and from the remote device. The
PSTN Call Manager handles events during an active connection.
The PSTN Call Manager handles incoming connection attempts,
whether they occur when the line is inactive or in use.
When the line is inactive, it will ring the telephone
and the ring cadence can be configured to be different
for each line or different per incoming phone number.
When the line is in use, it interjects two short beeps
into the voice stream to indicate there is an incoming
call.
The PSTN Call Manager will also generate Caller ID information
and send it out the POTS line at the appropriate time
for standard display on a telephone. It does this for
any incoming call, whether the phone is inactive or
in use.
Supported PSTN Call Manager RFCs and Features:
- Successful Connection
- Dial Tone
- User Busy
- Invalid Number
- Other Error Conditions
- Placing a Call On Hold
- Being Placed on hold
- Call Waiting
- Call Forwarding
- Conference calling
- Call Transfer
- Caller ID
- General Error Feedback.
- Off-hook erros
- Invalid Number
- RFC 3665 (Best Current Practices for SIP based PC
based call flows)
- RFC 3666 (Best Current Practices for SIP based PSTN
call flows)
The Unicoi Voice (VoIP) Gateway consists of the following modules:
*A reference design is
a sample electronics circuit design that shows engineers
how to utilize the latest developments in microchips
in their own products. Using a reference design as a
base, it is possible today for a device manufacturer
to incorporate a new technology into existing designs
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not long after.
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