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Linksys ATA
Administrator Guide
Document Version 3.1
Chapter 4
Configuring the PSTN Gateway (FXO)
How PSTN-To-VoIP Calls Work
How PSTN-To-VoIP Calls Work
PSTN-To-VoIP calls can be made with two-stage dialing only. The only authentication method available
is the PIN method.
The SPA3102 takes the FXO port off hook after a configurable number of rings. If PIN Authentication
is enabled, it prompts the caller to enter the PIN number followed by a # key. The Inter-PIN-digit timeout
is set at 10 seconds. Up to eight PSTN PIN numbers can be configured in the SPA3102. If the given PIN
does not match any of the PSTN PIN values, the SPA3102 plays the reorder tone to the FXO port for up
to 10 seconds, and then takes the FXO port on-hook. If the given PIN matches one of PSTN PIN values,
the SPA3102 plays dial tone to the FXO port and is ready to accept digits for the target VoIP number
from the PSTN caller. The collected digits are processed by the dial plan associated with the PIN
number.
Note
If Authentication is disabled, a default dial plan is used for all PSTN callers.
Terminating Gateway Calls
There are two call legs in a PSTN gateway call: the PSTN call leg and the VoIP call leg. A gateway call
is terminated when either call leg is ended. The SPA3102 takes the FXO port on-hook when the call
terminates so the PSTN line can be used again. The SPA3102 detects that the PSTN call leg is ended
when one of the following conditions occurs during a call:
•
The PSTN Line voltage drops to a very low value (this occurs if the line is disconnected from the
PSTN service or if the PSTN switch provides a CPC signal)
•
A polarity reversal or disconnect tone is detected at the FXO port
•
When there is no voice activity for a configurable period of time in either direction at the FXO port
When any of the above occurs, the SPA3102 takes the FXO port on hook and sends a BYE request to
end the VoIP call leg. On the other hand, when the SPA3102 receives a SIP BYE from the VoIP during
a call, it takes the FXO port on hook to end the PSTN call leg.
In addition, the SPA3102 can also send a refresh signal periodically to the VoIP call leg to determine
whether the call leg is still up. If a refresh operation fails, the SPA3102 ends both call legs.
Table 1-29
lists parameters for terminating gateway call parameters.
Table 1-28
Two-Stage Dialing
Parameter
Group
Description
Values
VoIP Caller
1/2/3/4/5/6/7/8
PIN
PSTN
Line
The PIN for VoIP Caller 1, 2, 3, 4, 5, 6, 7, or 8.
31-character string
VoIP Caller
1/2/3/4/5/6/7/8
DP
PSTN
Line
Specifies which dial plan to be used for this
VoIP caller. If 0, dial plan processing is
disabled; the given target number is dialed to
the PSTN as is.
Choice of 1 to 8