A “Detailed” PBX Explanation That Won’t Go Over Your Head… Hopefully.

A “Detailed” PBX Explanation That Won’t Go Over Your Head… Hopefully.

Hey guys. Today I’m going to talk about Private Automatic Branch eXchange, or “PBX.” Nowadays, it’s referred to anything related to telephony, but the term originated from the telephone exchange that consisted of manually operated switches connecting phone calls. PBX was initially used for a private network, e.g. a company’s office building. Everything connected to a PBX were eventually dubbed “extensions,” which is a term familiar to everyone who was ever asked for an “extension” during a phone call. Connections out of the private exchange are connected through trunk lines (Interesting fact: “Trunk” originated from the thick gray cables used in early telephony that reminded people of elephant trunks, and the telephone poles that were basically tree trunks).

I mentioned that PBX used to be manually operated by operators. You may remember old movies where an operator would actually answer the phone when a character wanted to make the call, and had to ask to be connected. Eventually switches were replaced by automated electromechanical, and then electronic switching systems, called PABX (Private Automatic Branch eXchange). PBX in the industry was then renamed PMBX (Private Manual Branch eXchange). The term “PBX” eventually came back into use in place of PABX because it was such a widely used term, and had familiarity with those who used the new switch operating systems. Those of you at work who have to dial “0” or “9” to dial out an “outside number” are using a PBX line. Now you have a term to go with the system you use everyday.

For those of you reading this and find the information dense, I’ll breakdown PBX’s three main duties:
1) Establishing connections (circuits) between the telephone sets of two users (e.g. mapping a dialed number to a physical phone, ensuring the phone isn't already busy)
2) Maintaining such connections as long as the users require them (i.e. channeling voice signals between the users)
3) Providing information for accounting purposes (e.g. metering calls)
Different manufacturers have developed different features for PBX, which include but not limited to: auto dialing, call forwarding, call transfer, call waiting, conference calling, music on hold, and voice mail.

The advent of the Internet has changed PBX systems with the use of VoIP. Yes, I’ve mentioned VoIP again folks. Right now, IP Centrex (contraction of Central Telephone Exchange) is very popular, but far from the original concept of PBX. We’ll have to see if VoIP technology will dominate this sector of telecommunications as much as it seems to be dominating the residential phone and cell phone industry.