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VoIP – PSTN Gateways and How They Do the Translation

PSTN and VoIP networks have co-existed for some time now. Calls can be made from one platform to the other with the help of translation signaling/media gateways. But how is this translation done and what are the main functions of a gateway?

PSTN and VoIP are two very different technologies. PSTN uses SS7/ISUP protocol for signaling and transfers media over traditional TDM channels on E1/T1 trunks.  VoIP on the other hand, uses SIP protocol for signaling and RTP protocol for the media. A gateway’s duty is to convert those protocols and formats from one to the other.

A gateway has three main functions:

  • Signaling Gateway (SG)
  • Media Gateway Controller (MGC)
  • Media Gateway (MG)

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