Where to Connect your Business’ Telephone Exchange – IP Network or PSTN – and why?
Designing a telephony system can be both simple and complicated. It can be simple if there are only few telephone units that you want to connect on a network – say in a small office building. It can be complicated if the design will involve thousands of telephone units scattered across towns, states and countries. But whether it’s a simple or complicated task, what is clear is that recent advancements in telecommunication systems are making the job of the designers lighter. These are also the reasons why modern telephone exchanges, unlike many decades ago, have sophisticated switching equipment, fast communication lines, and simplified numbering plans.
But in the first place, why would you care to understand telephony systems?
Well, the truth is that every time you dial a phone number to initiate a call, your concern about the telephone system is already there. How is that so? One, you want to connect fast. Second, you want a high fidelity call. Third, you want to be billed right on this call. Remember that every telephone company (or should I say telecom company – to sound more modern) charges different call rates. Even if you’re calling from a smartphone, a desktop IP phone, a softphone (like Skype) or an analog phone with rotary dials, you’re still using someone else’s telephone system, and you have to pay for that.
I wouldn’t tell here techniques or hacks to minimize the cost of your long distance calls. What you are about to learn is how to make your every telephone call worth it – in terms of cost, voice quality, and connectivity. Let’s continue by understanding how telephone exchanges work with this example.
Say from your New York City office, you want to call your friend in your Sydney headquarter using your IP desktop phone. You’ll dial 011 + 61 + (7-digit number) which is equivalent to the country code + area code + subscriber’s phone number. From your phone, you’ll be connected to a router, then the router will connect to your company’s Private Branch Exchange (PBX), then the PBX will connect to the Public Switched Telephone Network (PSTN), then to the PBX of your friend’s office in Sydney, then to the phone in her desk.
Another route is from the router, you’ll be connected to the IP Network, then to the router of your friend’s office, then to the PBX and to her phone. If your New York City office has a dedicated IP PBX for a big number of VoIP users, then from your IP phone, you should be connected first to this telephone exchange system before the router.
As soon as your friend grabs the handset, both of you are in “off hook” mode and the per minute charging rate now applies.
Now, aren’t you wondering why you still have to be connected to the PBX and PSTN if you can be routed direct to the IP network? This is where the complexity of telecommunication comes in. Let’s first define these stuffs. For clarity, let me borrow these lines from Wikipedia.
A Private Branch Exchange (PBX) is a telephone exchange or switching system that serves a private organization and performs concentration of central office lines or trunks and provides intercommunication between a large number of telephone stations in the organization.
The Public Switched Telephone Network (PSTN) is the aggregate of the world's circuit-switched telephone networks that are operated by national, regional, or local telephony operators, providing infrastructure and services for public telecommunication. The PSTN consists of telephone lines, fiber optic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables, all interconnected by switching centers, thus allowing any telephone in the world to communicate with any other.
Thanks Wikipedia for making stuffs clear. Now, the IP Network basically uses the internet to connect your call. The use of the internet as your communication line depends on your company’s current subscription – IP network or PSTN.
One of the differences between using the IP network and the PSTN is when it comes to the data transmission protocols and standards being used. IP network uses VoIP protocol and the ISDN (stands for Integrated Services Digital Network) standard. PSTN uses SS7 signaling protocol in the dedicated telephone lines. Here are other differences. When there is power outage, IP network is gone but PSTN is still up. With IP network, you can have free VoIP-to-VoIP calling both local and international, but with PSTN there is no free calling at all.
It should be clear then that even if you’re using an IP phone, you can still be connected to the IP network or the PSTN. So the question now is: if you have a business, to which network are you going to connect your PBX or telephone exchange system so that your every phone call is worth it? I suggest that you do your homework on that.
