Real-time communication (RTC) began with telephone during the second half of the 1800s, and almost immediately evolved into a big, worldwide, interconnected network of big companies and infrastructure.

Until a few years ago, telephony was a walled castle strictly guarded by huge corporations and almost nobody was able to completely understand how it was actually working. You got a chance to gain that esoteric knowledge by attending internal technical seminars and in-house schools, and even that knowledge was limited to the part of the system you were to work on (central office, last mile, PBX, and so on). Both the infrastructure carrying and routing the calls, and the applications answering and managing them, were ad hoc, rigid, not compatible with each other, and required huge investments.

Then two revolutions completely obliterated that old world. The first one was the VoIP telephony revolution, which brought an open protocol (SIP) to power, first in the application/PBX realm, and then in the infrastructure too. First to go was that steel box containing a proprietary PBX that could only be expanded by changing internal hardware cards made by that same company, serving only its own kind and model of hardware phones. It was substituted by a standard server with standard PC architecture, using off-the-shelf expansion cards, able to support any kind of standard-compliant phones. SIP then climbed from bottom to top, up to the very core of Big Telcos infrastructure. Today, all telecommunication infrastructures including those of Big Telcos and Carriers are running some version of the SIP protocol.

And the second revolution, which is ongoing right now and will take some more years to complete and bear fruits: WebRTC. This is a very misleading name; WebRTC does not require web pages and browsers at all. WebRTC is a set of standards for the encrypted interconnections of communication endpoints. This WebRTC standard happened to first be implemented in browsers.In the mean time it has become the mainstream way to communicate in the Internet of Things, spanning from smartphone apps to cars, lifts, shop cashiers, and point of sale.

Nowadays it's possible to build communication systems that outperform traditional voice, video, and conference services and offer advanced features for a relatively low cost. FreeSWITCH has been designed to make all of this easier, and we will go over its architecture to get a better understanding of how it works.

Don't be concerned if you don't grasp it all in one swoop. Learning takes time, especially RTC and VoIP. In fact, we recommend that you read this chapter more than once. Absorb as much as you can on the first pass, then come back after you complete Chapter 6, XML Dialplan. You will be surprised at how much your understanding of FreeSWITCH has improved. Then come back and skim it a third time after you have completed Chapter 10, Dialplan, Directory, and ALL via XML_CURL and Scripts; at this point, you will have a firm grasp of FreeSWITCH concepts. Give yourself time to digest all of these new concepts, and soon you will find that you are a skilled FreeSWITCH administrator.

Today, we live in an ecosystem of multiple RTC technologies, all coexisting at the same time: telephony systems (such as telephone switches and PBXs), the traditional analog phone (POTS lines or Plain Old Telephone Service), traditional telephone networks operated by carriers (PSTN or Public Switched Telephone Network), mobile phones (CDMA, GSM, LTE, and so on), faxes, WebRTC, smartphone apps, VoIP phones, and Enterprise systems.

FreeSWITCH's niche is right in the center of this ecosystem: it connects and accepts connections from all those technologies, it bridges and mixes them together, it provides interactive applications and services to users whatever their endpoint happens to be. FreeSWITCH is able to connect to external data services and to legacy in-house systems, to computer programs and business procedures. FreeSWITCH runs on Linux, Windows, and Mac OS X, as well as *BSD and Solaris. We have plenty of hardware choices, from big multiprocessor servers to Raspberry Pi. So, you can develop on your laptop, and then deploy on datacenter, or in an embedded device. Installing FreeSWITCH is discussed in detail in Chapter 2, Building and Installation.