Thursday, July 28, 2011

How Does An IP PBX Work?

Private Branch Exchanges (PBXs) began life as cost-saving measures. Although a business might have many employees with many phones only a small proportion are actually on the phone at the same time. Thus the business doesn't need as many lines to the phone company as they have employees, they need some smaller number. They make do by switching the local extension of whoever makes or receives a call onto one of those lines to the phone company.

This was done manually at first: you may have seen the old images of a person at a switchboard, pulling cables and plugging them into sockets, actually physically connecting a business's local phone cable to a line that goes to the outside world and the phone company.

Later on, PBXs could be made to do this mechanically without a human to do it, then electronically. But at the end of the day it all worked the same way: plugging one of many local extensions into an outside line, making a continuous (if temporary) connected circuit.

IP PBXs changed this. Packet-switching technologies like IP don't connect a continuous circuit: points in the network look at packets of information and decide where each one should go, then a device on each end "rebuilds" them and delivers them in whatever manner they're meant to be delivered.

An IP PBX is now the connection between a phone company's public voice network and a business's data network. Instead of switching people's phone extensions to a phone company line, voice is encoded into data packets and then delivered, piece by piece as data, to phones that know how to interpret them and rebuild them as voice. An IP PBX therefore acts a bit more like a router, sending the data (which can be voice) where it needs to go (which can be phones).

Because everything is switched as data, though, you can now do many other things quite easily: conferencing, sending voie to your computer instead of your phone, storing voicemail as files, and much more.

Almost all modern large PBX's (more than 100 phones) are IP based – IP/SIP is the protocol that the parts use to talk to each other. The phones/devices on an IP based PBX may be analog, digital, IP (VoIP), soft phones (software that emulates a phone on a PC, smart phone, or other device), or Fax over IP (FoIP).

What the parts are exactly changes from brand to brand: some system have chassis (or cabinet) based systems that have specialized cards for functions (trunks, voice mail, digital phones, analog phones, message port, call processors, conference calling … ) some have routers or gateways with PSTN cards and other functions that are software based in servers (or banks of servers).

At the highest level - they work like PBX's always have. They provide connectivity to the PSTN for a bunch of phones or other devices. They connect to the PSTN through trunks - DS0, DS1/T1, PRI, BRI, SIP, Ethernet, and more .....

The PBX configuration is the main item that governs your line and trunk strategy, your calling cost structures, the integrated calling options available for the desk phone, cell phone, and full messaging integration on the desktop PC and traveling laptop.

1) Not all IP PBXs are hosted. In fact, most IP PBXs are not hosted.

2) Traditional PBXs were not all analog. In the beginning, that was true, but most PBXs built from the late 1980's on were digital and used a technology called TDM to operate.

3) IP is also transmitted over copper wires - the same CAT 5 copper wires that can connect you to the internet, but not all VoIP traffic resides on, or ever touches the internet. Most VoIP traffic actually resides on the user's LAN or private WAN.

4) IP PBXs are not always "relatively inexpensive" either. Price a cisco lately?

5) An "open source from Asterisk" is not necessarily a good starting point. IN fact, if you don't know anything about IP PBXs, that would be the worst thing that you could do.

A simplified answer would be this: an IP PBX converts analog sound waves (your voice or DTMF tones) into IP packets, labels the packets, and guides them to the proper destination where they are converted back to analog sound waves so you can hear them. The technology works in a similar fashion to the technology that you use view a movie from YouTube on your PC.

There is a lot of additional technology in place behind this premise. You need the correct network hardware in place to properly route and switch the packets. You need a connection to the Public Switched Telephone Network (PSTN) so you can talk to users outside of your PBX environment, etc.

For free help navigating through the maze to decide what is the right fit for your business I suggest the no cost assisstance availabe here .... Business VoIP Solution

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