IP Telephony – Voice over IP (VoIP)

At its simplest, IP Telephony is just a way to carry voice from one place to another. What makes it so revolutionary is not so much due to any technical advantages, but simply that it is based on inexpensive and popular networking standards. You can buy the hardware at your local computer store. The details of the SIP protocol can be downloaded for free from the IETF, and IP networks can be built by anyone, at very low cost.

IP Telephony began as an experiment in carrying voice traffic across a packet network. The concept was simple: Run some voice traffic across a fixed-cost connection (piggy back it onto the data traffic), and avoid paying long distance charges between offices. Early equipment was expensive, but then again, so were long distance charges.

As the internet grew in popularity in the late 90s, the powerful (and free) Internet Protocols (IP) began to rapidly replace the almost ubiquitous Novell NetWare technology then popular in office networks (LANs), and it also became popular to layer IP on top of the various carrier circuits in use. The rise of the ISP began at this point as well. IP rapidly found use all over the place as a standardized all-purpose network protocol. Every network was becoming an IP network, so the awkward term “packetized voice” naturally became “IP Telephony” or “Voice over IP (VoIP)”.

A massive disruption has ocurred in the telecommunications industry. Old, complex, proprietary and obscure technologies have given way to well-documented, open-standards and popular protocols.

The challenge with IP Telephony is that the internet was not designed to carry voice traffic. The neat little packets being delivered all in a neat row, can too often end up more like this:

How Packets Sometimes Get Delivered

Human beings are not computers. When we talk, our brain expects to hear speech in a very specific way. It must be contiguous (no gaps), it must arrive in order (or sense make won’t it else), and any delay of more than a few hundred milliseconds is going to feel rude (“are you even paying attention?”). Computers can forgive all sorts of problems with communication, but the human ear is a bit more fussy.

In the early days of the internet, it was all but impossible to expect voice to pass reliably. Today, the opposite is true. IP Telephony is reliable, and more importantly perhaps, it is understood in the industry that everyone maintaining networks have a shared responsibility to ensure voice traffic passes without problems. In other words, current-generation networks are engineered to ensure voice quality.

Today, rather than purchasing expensive hardware to connect to limited physical circuits, IP telephony allows simple and reliable connections of multiple service types, all on a standard network server, running standard network hardware.

IP Telephony saves money, and opens the door to the full power of the internet. In fact, I think it would be safe to say the best is yet to come!

Next up we’ll dive into the details of what is required in an office network to support IP Telephony. In other words, how to VoIP enable your network.

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IP Telephony – The Emergence Of Data Networks

The technologies that run the internet were first developed in the 60s.

The network could be built as a mesh of nodes, and information could be sent in more than one direction—routing. Also, connections between nodes could be shared with all the types of traffic passing through. This is analogous to the highway networks of today. Many vehicles can be on the same stretch of road at the same time, and can be of different sizes and speeds, and can be coming from different places and going to different destinations, starting and ending at different times. It’s a bit more messy than a neatly-arranged and carefully-scheduled train, but it’s far less expensive, and the infrastructure is not sitting doing nothing in between trains.

A key difference between circuit-switched and packet-switched networks is that packet-switched data must be encapsulated in a wrapper containing address information. The network doesn’t really care what’s in the package, so long as the addressing information is intact. In the train-to-road analogy, each car needs a driver, but an entire train follows one locomotive.

Circuit-Switched (Public Telephone Network)

Packet Switched (Internet)

Your computer encapsulates the data you want to send in a packet, and if there is more data to send than can fit in that packet (there are limits on how large a packet can be), it will send another, and another … as many packets as needed. At the other end, all the packages are opened, the data inside is recombined, and the other end then has a photo, or document, or video, or snippet of sound, or whatever it was you sent. Often, missing packets can be retransmitted, and packets can take multiple routes to reach their destination.

Circuit-switched networks have many benefits over packet-switched networks, however it is difficult to justify their cost, as they tend to be limited in their use. An analogy would be the high-speed passenger rail networks of Europe. You cannot carry freight, and you will never be able to justify the cost to build a station next to your house. Roads, on the other hand, are far more limited in terms of speed and efficiency, but they can be built everywhere, and can carry everything from bicycles to trucks to buses.

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IP Telephony – Some History

Humans love to talk. Any discussion of IP Telephony needs to always keep first and foremost the understanding that the primary purpose for telephones is to allow us to talk to each other. It seems obvious, but this simple fact sometimes gets lost in technical details.

Our vocal cords, tongue, lips and teeth allow us to create complex vibrations in the air around us, which when recieved by another person’s ear (and interpreted by their brain) allows the transfer of information from us to them.

The essential parts of the telephone were figured out through experimenting with ways to convert sound vibrations in the air into electrical signals, and then convert those electrical signals back into sound vibrations at the other end. Electrical signals have an advantage in that they can travel over vast distances, and do so far more quickly than sound waves can.

The first telephones were fascinating, but not very useful. You had to string a wire between you and the other end, hook up a battery, and talk really loudly.

Then, somebody got clever and realized if you wire everybody’s line into a central office and hire a bunch of people to sit at that central location and answer calls, you could power everything from there, and have those operators move plugs around to connect people together. This system was incredibly labour-intensive, and also prone to all sorts of errors and ‘human’ factors, but without it the telephone might never have been anything more than an interesting science experiment.

The first automatic telephone switch was invented by an undertaker, who believed that one of his town’s switchboard operators was sending all calls for ‘the undertaker’ exclusively to her husband, his competitor. The Step-by-step Switch revolutionized the industry by automating the switching of connections between the two ends of a circuit, with you doing the work of selecting the circuit you wanted using the dial on your phone.

For a hundred years telecommunications took place across this circuit-switched network. The circuit created every time you made a phone call was dedicated to your call, and nothing else. The closest analogy I can think of is that of a railroad network. All the switches and signals that have to line up just to support one train, and no other trains are permitted on those sections of rail until that train has passed. Running two trains at the same time requires two sets of tracks.

In the next article in the series we’ll talk about The Emergence Of Data Networks, which are essential to IP Telephony, as they are based on packet-switching rather than circuit switching.

IP Telephony—also referred to as Voice over IP (or simply VoIP)—is packet-switched voice, rather than the circuit-switched voice of decades past.

Stay tuned for the next article in the series: IP Telephony – The Emergence Of Data Networks

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