Reference / Voice
VoIP–PSTN gateways: test the call path, not the feature list
A VoIP–PSTN gateway translates between packet voice and a telephone interface. It is not just a connector: deployment must align numbering, signalling, codecs, tones, network reachability and the rules of the connected line.
Map both sides of every call
Document source and destination number format, port role, routing rule, signalling, negotiated media and disconnect behaviour. A port for a telephone and a port for a line have different electrical expectations.
SIP and SDP have distinct documented session-control and session-description roles. RFC 4733 separately describes an RTP payload for DTMF, tones and telephony events; test the required call behaviours rather than treating setup as proof of every function.
Use a real acceptance test
Test inbound and outbound calls, answer and release, two-way audio, required DTMF, recovery after loss of power or network, and only features authorised by the connected service.
Record gateway configuration, address plan, firmware version and cable map locally. Agree emergency-call and power-failure behaviour with responsible operator and site owner; do not assume a generic gateway preserves every traditional-line feature.
State the service boundary
A gateway cannot create a telephone service that the connected line or provider does not supply. Keep commercial, regulatory and routing responsibilities outside the device feature list.
When replacing a gateway, test the replacement in parallel where possible and preserve the old configuration securely until the new call path is accepted.