Configuring the PSTN (FXO) Gateway on the SPA3102
How PSTN-To-VoIP Calls Work
Cisco Small Business ATA Administration Guide
96
6
NOTE
For information about configuring the timer values for the above scenarios, see
“FXO (PSTN) Timer Values (sec) section,” on page 214
.
For information about configuring caller authentication on the SPA3102, see
“VoIP-
To-PSTN Gateway Setup section,” on page 211
.
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. When the call
terminates, the FXO port goes on-hook so the PSTN line is available for use. The
ATA device 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.
•
There is no voice activity for a configurable period of time in either direction
at the FXO port.
When any of the above conditions occur, the ATA device takes the FXO port on
hook and sends a BYE request to end the VoIP call leg. On the other hand, when
the ATA device 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 ATA device 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
ATA device ends both call legs.
On the SPA3102, these settings can be configured on the Voice tab > PSTN Line
page. For more information, see
“PSTN Disconnect Detection section,” on
page 216
.
On the SPA8800, these settings can be configured on the Voice tab > Phone page.
For more information, see
“FXS Port Polarity Configuration section,” on
page 183
.