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What is a VoIP Gateway?

What is a VoIP Gateway?

A VoIP Gateway allows you to convert between a legacy telephony connection, such as E1/T1/PRI and a modern VoIP connection using SIP. This is known as "digital gateway" because the voice media is converted between a digital TDM connection and a VoIP connection. The conversion can go from SIP to TDM, TDM to SIP or even SIP to SIP for the purposes of failover or transcoding. In a TDM-to-SIP deployment, the gateway significantly reduces operating costs by connecting a legacy business phone system with dynamic SIP trunking services. SIP-to-TDM deployments use the VoIP gateway to connect a modern SIP communications system with T1/E1/PRI service from legacy carriers. There are many applications for VoIP media gateways. 


Public Switched Telephone Network T1/E1/PRI to VoIP

A VoIP gateway can connect a modern VoIP-only system, for example a virtualized IP PBX, to a PSTN PRI trunk.

VoIP Gateway Diagram: VoIP to PSTN


VoIP Provider to Legacy PBX

An IP Media Gateway can be used to upgrade a legacy business phone system allowing it to use a SIP trunk out to an ITSP. SIP Trunks are more cost-effective than expensive legacy T1 lines.

VoIP Gateway Diagram: SIP to ITSP


Legacy PBX to IP PBX Migration

The VoIP gateway also acts as a bridge connecting a legacy PBX via a PRI interface and an IP PBX via a SIP connection to support a migration initiative.

VoIP Gateway Diagram: Legacy PBX to IP PBX


Terms / Acronyms:

  • VoIP - Voice over IP
  • SIP - Session Initiation Protocol
  • IP - Internet Protocol
  • TDM - Time Division Multiplexing
  • PRI - Primary Rate Interface
  • ISDN - Integrated Services Digital Network
  • PSTN - Public Switched Telephone Network
  • ITSP - Internet Telephony Service Provider

VoIP gateway may also be referred to by any of the following:

  • IP Media gateway
  • SIP gateway
  • Voice gateway
  • TDM gateway
  • PSTN gateway
  • PRI gateway
  • ISDN gateway
  • Digital Telephony gateway

The terms VoIP Gateway and IP Media Gatewayare the most common names for this type of device.