How does the whole phone system work?

The main question I am trying to understand:

What is the maximum extent to which a phone system is reasonably “self-hostable”?

Understanding what is and isn’t possible or feasible has been difficult since there is such a steep learning curve with phone related technology. I’m lost with all the vocabulary and amazed at how phone systems have managed to stick around this long considering how legacy some of this technology seems.

  • DID
  • SIP
  • PBX
  • POTS
  • PSTN
  • IAX
  • CallerID
  • SRTP
  • RCS

I am approaching this from the perspective of self hosted computer systems, email for example.

To self host email to a maximum but reasonable extent, I would need:

  • A computer to run email software on (such as exchange)
  • A domain name
  • A connection to the internet (ISP)

There are varrying degrees of “self-hostability” for these items, however.

Domain name

The most self-hosted way you typically acquire a domain name is by going through a registrar since it is not feasible to pay ICANN or whoever to become your own registrar and then purchase your own TLD or some such thing. It is generally agreed upon that unless you’re a giant company capable of purchasing your own TLD, you’re just going to have to go through a registrar. Okay, fine.


The most self-hosted way is to just purchase an IP address from an an internet service provider since it is not feasible for someone to setup their own infrastructure for connecting to the internet backbone to become their own ISP, (though not impossible!). You’re just going to have to buy your IP address from an ISP. Okay, fine.

A computer

The distinction between self hosted and non-selfhosted is very clear here: if I can touch the computer with my hand, it is self hosted. Of course you can also argue that a VPS is “self hosted” in the sense that you’re managing the OS but someone else is managing the hardware, but let’s say we’re trying to be in control of as much of the infrastructure as possible, so that means server rack in your basement.

The internet

I have a fairly clear understanding of how internet traffic works via your computer, your ISP, the internet backbone, DNS, etc. But the topology of a phone network is an entirely different beast.

The phone system


Main question

Back to my main question:
What is the maximum extent to which a phone system is reasonably “self-hostable”?

  1. Where should I start reading to get an introductory understanding of phone systems?
  2. PSTN - is this outdated?
  3. What are the corollaries to my email example for the phone system?
    3.1. Can the services of be self hosted?
    3.2. How do you buy phone numbers like how you buy IPs?
    3.3. Where does Asterisk, FreePBX, etc. fit in to all this?
  1. Wikipedia has lots of information on how the system works:
    PSTN network topology - Wikipedia

  2. PSTN is still in use and people still use phones

  3. If you are asking about hosting your own phone number, it’s not at all a simple process and far bigger concept than I have time to cover here. You can buy numbers from places like VoipMS and here in the US under Telecommunications Act of 1996 the Local Number Portability (LNP) for landline phone numbers allows them to be ported to other carriers, also the Wireless Local Number Portability (WLNP) exists now and specifically applies to mobile phones and switching carriers. You need a device for the phone number to interact with, a phone is basic starting point but a PBX such as FreePBX extends from a place to land the phone to features such as voicemail, routing to other extensions, and many other features.

Time is always the enemy… How much time do you have? If time is short, hire a company to buy, install, and manage it. If time is “endless”, then you have a lot of it to spend on learning and setup.

You’ll still need some kind of hardware to run on this system, be it single phone or PBX, Make sure to buy a new enough phone that it is supported in your system, I have a bunch of old Cisco phones that can be challenging to get going in FreePBX. And time is certainly against me when I try to teach myself this stuff. But I do have use cases that I can put in place very soon, so I need to battle with time and carve out a slice. Thankfully not needed for my day job.

Thankfully in this case time is endless since I’m moreso interested in learning about it and implementing for my own personal use.

I’m thinking I should just try to host FreePBX and go from there, sounds like that is a base starting point that would teach a lot.

Interesting, so FreePBX does do some of the services that or the like charge for.

Just be careful on the handsets you choose, and you might want to buy a used POTS interface card so that you can bring the old analog phone lines into the system.

Word of warning, some used phones you might find on ebay could be locked to work with their controller. Cisco being one of the worst for this. There are workarounds and community firmware that can fix some of this.

I think you have a great idea in trying to learn FreePBX for your goal.

I’m the resident nerd in my company, and we made a huge shift about 3 years ago now due to dated technology and brought a lot of infrastructure in-house we now run everything, except our email servers, on-premise.

I knew nothing about VOIP and dove in head first with FreePBX and have not looked back. For not mission critical use… I cannot recommend The Crosstalk Solutions’ FreePBX series enough. Walks you through step-by-step (Tom has some WONDERFUL videos from back in the day on VOIP, too). While not strictly teaching you VOIP concepts you will get exposure to a lot of basics in setting up your own phone system… DIDs, SIP, PBXs, SRTP, etc.

1 Like

Thanks for the link, I’ll have to go through those when I have time to get back to experimenting with voip in my lab.

1 Like