The HT813 is an analogue telephone adapter featuring 1× FXS port and 1× FXO port, enabling remote call origination and termination to and from the PSTN line. The FXS port extends VoIP service to one analogue device, allowing users to take advantage of VoIP on their existing analogue handsets. Where most ATAs provide only FXS or only FXO functionality, the HT813’s hybrid design means a single device handles both — connecting an analogue desk phone to a VoIP platform while simultaneously keeping a PSTN line available for backup or outbound calling.

Key Highlights

• 1× RJ11 FXS port for connecting an analogue phone or fax machine
• 1× RJ11 FXO port for connecting a PSTN telephone line
• 2 SIP profiles supported across the FXS and FXO ports
• Dual 100Mbps WAN and LAN ports
• Ultra-compact desktop form factor — minimal desk footprint

PSTN Lifeline & Failover Protection

The HT813 features lifeline support — the FXS port is hard-relayed to the FXO port in the event of a power outage, ensuring a connected analogue phone can still make and receive PSTN calls even when power or internet connectivity is lost. This makes it particularly well-suited to South African deployments where load shedding is a routine consideration. A failover SIP server capability automatically switches to a secondary server if the primary loses connection, adding a further layer of telephony resilience.

• PSTN lifeline — FXS hard-relays to FXO port during power outage
• Failover SIP server for automatic switchover if the primary SIP server goes offline
• Simultaneous VoIP and PSTN line connectivity
• Supports remote calling to and from the PSTN line via the FXO port

HD Voice, Fax & Codec Support

The HT813 delivers HD voice quality through wideband codec support, with a broad range of standard codecs ensuring compatibility across different VoIP platforms and SIP trunk providers. T.38 compliant Fax-over-IP is supported for reliable fax transmission across VoIP links, with automatic G.711 pass-through fallback ensuring compatibility with legacy fax infrastructure.

• HD voice quality with wideband audio codec support
• G.711 (Annex I/II), G.723.1, G.729A/B, G.726, iLBC codec support
• T.38 Fax-over-IP with G.711 fax pass-through fallback
• G.168-compliant echo cancellation and dynamic jitter buffer for clear voice quality
• Layer 2 (802.1Q VLAN) and Layer 3 (ToS, DiffServ, MPLS) QoS support

Rich Telephony Features

Telephony features include caller ID display and block, call waiting, call transfer (blind and attended), call forward, hold, do not disturb, and 3-way conferencing — covering the full feature set expected of a business desk phone, delivered through the analogue handset already in use.

• Caller ID, call waiting, call transfer, call forward, hold, and DND
• 3-way conferencing
• Message waiting indication and multi-language prompts
• Flexible dial plans for call routing control

Security & Easy Management

Strong AES encryption with a unique security certificate per unit protects all calls and credentials. Multiple provisioning methods including TR-069, HTTP, HTTPS, and TFTP make automated mass deployment straightforward, and the HT813 is compatible with GDMS — Grandstream’s free cloud management platform — for centralised configuration, firmware management, and monitoring.

• AES encryption with per-unit unique security certificate
• TLS and SRTP for secure call transmission
• TR-069, HTTP/HTTPS, and TFTP provisioning
• GDMS compatible for free centralised cloud management
• SSH, Telnet, and web UI for local management

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