I’ll break it down.

You either have:

  1. Rotary (You don’t have this but I wanted to put it in the list) These use pulse dialing to tone dial. The discrepancies of which you may find somewhere else online.
  2. Analog Phones that connect to a 66 or 110 block than have trunk lines supplied by a PRI (big gray cable with a lot of wires split out into the block from it.
  3. Digital Phones (The in-between) The phones are powered via phone cables (or ethernet) it only uses the central (blue & blue/white) wires on ethernet when ethernet is used as the wiring standard T568A and T58B are backwards compatible for RJ11 to plug directly into a RJ45 port. They are powered but not by 802.3af PoE. Instead it’s powered by directly connecting to a line card using RJ11/RJ12 or RJ45 ethernet cabling. The line card in the phone system is what sends the power through the line. Therefore, you can’t use your PoE switches for digital phones. However, the whole phone system itself is like 1 big analog telephone with multiple lines and therefore works as such since it was designed to interact with a standard 66 or 110 block and punched down into one to connect it to a PRI from the telephone service provider to get on the PSTN (public switched telephone network). To alleviate the cost of lines on the PSTN a service provider would sell access that it already has over the internet using SIP (session initiation protocol) trunks over a standard internet connection. I would think “Well, that’s 1:1 so how are they saving anything?” well, the ITSP or Internet Telephone Service Provider can do time division of the resource since you’re not always making a call and therefore such a line can be used by someone else whilst you’re not using it making a scarce resource more available and cheaper. It can also do more intelligent routing since the voice data is travelling along a packet switched network instead of a circuit switched network. Some businesses want to save money and keep their digital phone systems but want to pay less for their telephone service (access to the old dying decrepit PSTN is expensive but necessary). The solution then is to use an ATA or Analog Telephone Adapter (sometimes called a gateway) that sits between the digital phone system and an ethernet port on your LAN (Local Area Network) switch. On the ATA you program your SIP trunk login information from your ITSP connect it to your phone system and you’re ready to use the service! However, all management of how the phone system deals with line management will still be with the phone system itself and doesn’t have room to grow with modern features that are being required of businesses lately. This is where VOIP comes in.
  4. Another phone level I would say would be IP phones that connect to an analog connection. If anything this could have been a 3.5 in the list of 4.
  5. If you’re looking to get a new phone system a VOIP system is where you should start. Many includes native SIP support, IP phones that are powered by PoE. The only real constraint that you must consider is if you need access to multiple ITSPs for redundancy and if you want the PBX (Private Branch Exhanger) or Phone Controller for simplicity’s sake to sit on-premise, in the cloud, be a baked in solution from a provider, or host your own cloud based PBX. Check out FreePBX if you’re looking for a DIY version of a PBX.

I’ll stop there for today. Rambled on a bit about the Digital phones since I feel that there are many businesses that have gone this route but are beginning to see their phone system slowly dying and line cards are becoming harder to find as they aren’t manufactured anymore. Hope you enjoyed the article! 🙂

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