What is a VoIP gateway?
Published
A VoIP gateway is a bridge between classic telephony and IP telephony. It sits between the two and translates, so that a call can cross from one technology to the other without either side having to change.
That stays abstract until you look at what is actually on the classic side: a PBX with years of depreciation left in it, a fax machine, a franking machine, a door intercom, a lift emergency phone, an alarm dialler, a card terminal. None of them speak SIP and most of them never will. The gateway is what keeps them working after the line behind them has become a SIP trunk.
A bridge, and then some
Once a gateway is in place, a call has more than one way out of the building. You can build backup routes so that a call still completes when the primary path is unavailable, and you can route by destination — PSTN, mobile or SIP, whichever suits that number.
Newer devices do more than convert. beroNet gateways can be extended with apps: the Survival Branch Appliance app turns the gateway into a local fallback that keeps a site telephoning internally when the hosted PBX becomes unreachable. A failover switch does the equivalent in hardware for the line itself.
Knowing when it breaks
A gateway that fails quietly is worse than no gateway. Monitoring and alerting belong in the device rather than in a separate tool. On beroNet hardware that alerting is part of beroCloud, which also handles the unglamorous half of the job: remote configuration, scheduled firmware updates, backup and restore across a fleet of sites.
One point about licences
Calls between the PSTN interfaces — BRI, PRI, FXO, FXS — and SIP need no session licence. Session licences apply to SIP-to-SIP traffic only, which is the SBC role: two IP systems talking to each other through the device. A pure ISDN-to-SIP or analogue-to-SIP gateway needs none of them.
Choosing one
Gateways have been on the market for a long time and they are not equal. The useful questions are narrow. Which interfaces does the site have today, and which might it have in three years? Does the device do echo cancellation and T.38 fax properly? Can it be managed without a site visit? And what happens to the telephones when it fails?
On the beroNet side the interface question is answered by modules rather than by models: the ISDN gateways and the analogue gateways are the same enterprise SBC platform with a different module fitted, and the module can change later without the device changing.