Grandstream HT813 Analog FXS VoIP Gateway with Gigabit NAT RouterDescriptionSpecificationsShipping The HT813 is an analog telephone adapter that features 1 analog telephone FXS port and 1 PSTN line FXO port in order to offer backup lifeline support using a PSTN line. The integration of a FXO and FXS port enables this hybrid ATA to support remote calling to and from the PSTN line. For added flexibility, the FXS port extends VoIP service to one analog device. Users can convert their analog technology to VoIP thanks