what is pstn full form

 What is PSTN full form? VoIP Vs PSTN, PSTN to VoIP converter.

The PSTN stands for the public switched telephone network.  PSTN full form has two main things. One is public and another is switched.  Public means that the PSTN can be connected from anywhere and switched means the technique for setting up a voice channel.  PSTN is the legacy network based on SS7 switching elements. Which uses ISUP based signalling over E1/T1 links for setting a dedicate voice circuit.  As SS7 uses common channel signalling (CCS), the voice and signalling have two different channels. The full form of PSTN is very popular as most of the people in the world at any point in time have used PSTN phones.  No one uses PSTN full form while using PSTN phones.

There is now newer telephony, called VoIP. VoIP is based on Internet technology. VoIP uses a packet-based network for setting up a virtual path for voice. But the PSTN still is the backbone of telephony.  So there is a need to convert PSTN to VoIP and vice versa.  In the below section, we will discuss VoIP vs PSTN and PSTN to VoIP.


Both technologies enable a subscriber to make and receive a voice call. But VoIP and PSTN are very different on the network level.  Initially, VoIP was always outside of the telecom network.  If a VoIP client was running on a mobile phone, it was just using internet data from the GSM network. But with the LTE, which allows to connected non-3GPP network to LTE EPC,  now it is possible that a mobile operator using VoIP to connect its mobile subscribers via the internet, but it looks as they are connected to the gsm mobile tower.  WiFi calling is one of the examples, where a mobile operator uses an existing internet connection between a mobile phone and an LTE EPC network.  So VoIP Vs PSTN covers mainly the technical network differences along with user-level usage.  The following are the key points for VoIP Vs PSTN.

  1. VoIP uses internet technologies while PSTN uses SS7 based E1/T1 lines for signalling and voice or media.
  2. In VoIP signalling protocol is SIP, in PSTN, the signalling protocol is ISUP.
  3. There is no dedicated bandwidth in a VoIP call, as it uses the internet, which is a shared connection. While in PSTN, there is a dedicated E1/T1 channel for the voice calls.
  4. PSTN guarantees the quality of service, while VoIP does not, because of common internet connection for multiple subscribers.
  5.  VoIP does not need an additional infrastructure to support voice over the internet. In can use the same existing internet line. But PSTN needs dedicated lines.
  6.  Generally, VoIP provides low cost calls, while PSTN does not, especially while international roaming.
  7. For VoIP, a special VoIP client or VoIP phone is required. While in PSTN, it works on every basic or smart gsm phone, no need for a special client. 

PSTN to VoIP converter:

After the VoIP, both legacy PSTN and new internet-based telephony coexist in the world of telecommunication.  Bridging requires between PSTN and VOIP.  VoIP to PSTN converter does the bridging, VoIP to PSTN converter also named as PSTN gateway.  In real life example, we have skype which allows you to make a call to a GSM phone number from a Skype client. During the call, the skype VoIP network converts PSTN to VoIP and vice versa.

The converter has two components. One is signalling converter gateway and the other is media or voice converter gateway.  Signalling converter converts the signalling from one protocol format to another, for example, a gateway which converts SIP protocol messages to ISUP protocol messages (vice versa), is a PSTN to VoIP converter for signalling.

For media, a media gateway is used. MGCP is the protocol that controls a media gateway for converting one type of media to another.  In gateway, one side is PSTN E1 lines and another side is IP lines for VoIP (E.g RTP media)


Scroll to Top