What is PSTN’s 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 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 to set up a virtual voice call path. But the PSTN still is the backbone of telephony. This brings a need to convert PSTN to VoIP and vice versa. The below section 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 setting up the calls and other services. Initially, the VoIP network does not connect to the telecom network. If a VoIP client was running on a mobile phone, it just used 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, a mobile operator may use VoIP to connect its mobile subscribers. An internet network is the same as a gsm network for a mobile device. WiFi calling is an example where a mobile device connects to the WiFi for services.

So VoIP Vs. PSTN mainly covers the technical network differences and 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, the signaling protocol is SIP. In PSTN, the signaling protocol is ISUP.
  3. There is no dedicated bandwidth in a VoIP call, as it uses the internet, a shared connection. While in PSTN, there is a dedicated E1/T1 channel for 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 during international roaming.
  7. For VoIP, a special VoIP client or VoIP phone is required. At the same time, PSTN works on every essential or smart gsm phone, with no need for a special client. 

PSTN to VoIP converter:

After the VoIP, legacy PSTN and new internet-based telephony coexist in the telecommunication world. Bridging requires between PSTN and VOIP. VoIP to PSTN converter does the bridging, and VoIP to PSTN converter is also called PSTN gateway. In a 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 signaling converter gateway, and the other is a media or voice converter gateway. A signaling converter converts the signaling from one protocol format to another; for example, a gateway that converts SIP protocol messages to ISUP protocol messages (and vice versa) is a PSTN to VoIP converter for signaling.

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