Acronyms and Definitions

Private Automated Branch Exchange . A PABX is as sophisticated piece of equipment which connects an office to the telecommunications network and allows many workers to share only a few telephone lines. Advanced features such as voicemail, hold, transfer, least cost routing and more are also provided by PABXs. A PABX without the sopihisticated features is known as a PBX - a private branch exchange.

Plain Old Telephone System . The name says it all.

Public Switched Telephone Network . The standard telephone network used today.

Quality of Service . Exactly like it says. It is a way to mark some Internet traffic as being more urgent. For example, one might mark voice traffic as being "important to get there in real time, but if there is a huge delay, just drop the packets", where as downloading emails could have a QoS saying "just get the data when there is unused space on the line to my house". thus if you use both applications, whenever you use VoIP, it will be guaranteed a higher priority than emails. QoS is not implemented on an Internet-wide basis, though there is a lot of hardware that can deal with QoS parameters.