Grandstream HT503 Voip GatewayHandyTone 503 is a hybrid Analog Telephone Adapter (ATA)and VoIP Router. It features both an FXS (analog telephone) port and an FXO (PSTN) Port so you can have backup lifeline support using the PSTN in the case of a power outage. It also integrates 2 10 100 RJ45 ports with an integrated high performance NAT router. The HT503 includes a status LED indicator for power, telephone, PSTN line, network, and Message Waiting Indication. Specifications 1 FXS