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

The PSTN stands for the public switched telephone network.  The full form has two main words. One is public, and another is switching.  Public means that the PSTN can be connected from anywhere, and switching means the technique for setting up a voice call over a dedicated path.

PSTN is the legacy network based on SS7, which uses ISUP protocol over E1/T1 links for setting a dedicated voice circuit.

The SS7 uses a common channel signaling (CCS) technique. In CCS, the voice and signaling have two different channels or paths. For signaling, a network can also use Sigtran.

The full form of PSTN is prevalent as most of the people in the world at any point in time have used PSTN phones.  No one uses PSTN’s full name while mentioning PSTN phones.

Now there is a relatively newer telephony, named VoIP. VoIP uses Internet technologies. VoIP uses a packet-based network for setting up a virtual path for voice calls. But the PSTN still is the backbone of telephony.  This brings 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 voice calls. But VoIP and PSTN are very different in the way they set up the calls and other services.  In the beginning, the VoIP network does not connect to the telecom network.  If a VoIP client was running on a mobile phone, it was just using internet data from the GSM network. A mobile operator was not aware of any VoIP calls.

But with the LTE, which allows connecting non-3GPP (WiFi) networks to LTE EPC.  With LTE it is possible that a mobile operator may use VoIP to connect its mobile subscribers. For a mobile device, an internet network is the same as the gsm network.  WiFi calling is an example, where a mobile device connects to the WiFi for services.

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 signaling 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 a shared internet connection for multiple subscribers.
  5.  VoIP does not need an additional infrastructure to support voice over the internet. It 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, with 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 a signalling converter gateway and the other is a media or voice converter gateway.  Signalling converter converts the signalling from one protocol format to another, for example, a gateway that 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 the gateway, one side is PSTN E1 lines and another side is IP lines for VoIP (E.g RTP media)