The difference between VoIP and PSTN Telephony

The difference between VoIP and PSTN Telephony

Internet telephony is not a new technology – it has been around for many years in one form or another, but only recently has it become reliable and ubiquitous enough to be a serious choice for business. While Internet telephony was once an often haunted oddity for unreadable and dropped calls, these days a well-planned and implemented VoIP system can deliver the call quality and reliability that rivals mobile phone or landline calls.

How VoIP works

To understand how VoIP, short for Voice over Internet Protocol, works, it's helpful to compare it to how conventional phone calls operate. When you place a “regular” telephone call using the public switched telephone network (PSTN), otherwise known as the Plain Old Telephone Service (POTS) you use what is called a circuit-switched telephone. This system works by creating a dedicated channel (or circuit) between two points for the duration of the call. These telephone systems are based on copper wires that carry analog voice data over dedicated circuits.

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This is in contrast to the latest internet phone networks based on digital technologies. VoIP, in contrast to PSTN, uses what is called packet switching of telephony. Using this system, voice information at its destination in numerous individual network packets over the Internet. This type of communication presents special TCP/IP challenges because the Internet was not really designed for the kind of real-time communication a phone call represents.

The difference between VoIP and PSTN Telephony

The difference between VoIP and PSTN Telephony

Individual packages can – and almost always – take different paths to the same place.
It's not enough to simply get VoIP packages to your destination. Yhey must arrive through a fairly narrow time window and be assembled in the correct order to be intelligible to the recipient. VoIP employs technology encoding and compression schemes (see G.7xx for more information) to reduce the size of voice packets so that they can be transmitted more efficiently.

PSTN Versus VoIP: A Feature Comparison



  • dedicated lines
  • Each line is 64kbps (in each direction)
  • Features such as call waiting, Caller ID and so on are usually available at extra cost.
  • Can be upgraded or expanded with new equipment and line supply
  • Long distance is usually per minute or minute bundled subscription
  • Wired landline phones (those without an adapter) usually remain active during a power outage
  • When making a 911 call that can be traced to your location
  • All channels carry over from an Internet connection
  • Compression can result in 10Kbps (each way)
  • Features such as Call Waiting, Caller ID and so on are usually included free with service.
  • Upgrades usually only require bandwidth and software upgrades.
  • Long distance is often included in the regular monthly price.
  • Lose Power, Lose Phone Service Without Power Support In Place
  • 911 emergency calls cannot always be assigned to a specific geographic location

DID YOU KNOW? How to pronounce VoIP

There are three popular ways of saying it, with none being a definitive “right” way. All are correct.

  • Some people will use the full acronym, pronouncing each letter “VOIP”.
  • Some people will use use the first two words combined with IP (pronounced as separate letters). This is actually more like a “Voice-Over-IP” phrase.
  • Some will say the acronym as a word, just as it looks (like empty with only ap at the end) “voyp”.

To avoid the situation altogether, if you are not comfortable using the term VoIP in a conversation, you can simply say “Telephony via the Internet”.



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