What is SIP Trunking? And How Does it Work?

SIP trunking is a method of creating trunks based on Session Initiation Protocol (SIP) in which phone systems can communicate through Internet instead of traditional wired phone lines.

SIP trunking is provided by VoIP service providers same as traditional telephone operating companies. Though it uses an existing internet connection instead of separate wired lines, the operational and maintenance cost minimized significantly up to 60-80%.

How does SIP trunking work?

SIP is the base protocol used in SIP trunking for voice and video communication in a Unified Communications (UC) solution across a data network. It eliminates the physical connection between the phone company and user. An SIP trunk is installed virtually over user’s existing internet connection and therefore replacing the need for hardware, analog wired lines, circuit boxes to maintain for connection to the PSTN (service provider).

SIP trunks can be shared by multiple extensions simultaneously which reduces the maintenance and operational cost drastically.

Benefits of SIP trunking

  • It is very cost effective.
  • Easy to scale.
  • Less maintenance required
  • Service providers can also offer some additional features like encrypted voice calls, DoS protection, virtual inbound numbers, usage and performance reporting etc.


It is a smart solution against the tradition telephony systems and also PRIs. With lots of benefits it also has some limitations. The voice quality cannot be guaranteed as it requires a high speed and consistent internet connection. In areas where internet speed is comparatively low, voice quality may be poor. Also it works on Internet which requires electricity, hence no electricity means no calls.