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SIP trunking. The difference between PSTN, ISDN and VoIP.

Years ago when VoIP first appeared on the scene, in the time of dial-up Internet, it was associated with poor audio quality and dropped calls. Today it is no longer a problem, thanks to the increased availability of broadband Ethernet services. Large and small companies, public administration organizations worldwide opt for VoIP, while some other enterprises are still hesitant to make the move.

It might be just the right time to learn more about VoIP technology and SIP trunking: the largest telecom providers all around the world stop offering ISDN and PSTN in 2018 and have announced complete phasing-out over the next ten years.

Before going into details about the benefits of VoIP technology and SIP trunking, let’s take a glance at traditional technology.

What is PSTN? The difference between PSTN and ISDN.

PSTN (Public Switched Telephone Network) also referred to as POTS (Plain Old Telephone System) is a traditional telephone system that uses copper lines to carry analog voice data, allowing phones all over the world to communicate with each other. A dedicated circuit is established between the two points for the duration of a transmission. In the early days, operators manually connected one party of a phone call to another. Today switching is automated and PSTN is almost entirely digital.

ISDN (Integrated Services Digital Network) is a digital version of a telephone line, it allows transmission of voice and data over copper lines offering more features, higher quality and faster call setup capabilities in comparison to the classic telephone system. 

VoIP technology and SIP trunking.

VoIP (Voice Over Internet Protocol) is the IP-based version of telephone line which uses packet-switched telephony, where voice, data or video travels to the destination in network packets over the Internet. Once arrived, the packets are assembled in the correct order.

SIP (Session Initiation Protocol) is a signaling protocol used for multimedia communications, which determines the rules of how two points set up, manage and terminate a connection.

SIP trunking – is a direct connection between an organization and an ITSP (Internet telephony service provider). SIP trunks are responsible for routing the packets back and forth over the network, using IP-based data network to deliver voice, video and data.  

The term “trunk” came from circuit-switched telecommunications where it referred to as a dedicated physical line. In SIP trunking though, connection between telephone systems is established over a virtual line.