PABX

Private Automatic Branch Exchange. A European name for a Private Branch Exchange (PBX). See Private Branch Exchange.

Packetized Telecom

The public switched telephone network, or PSTN, is a circuit-switched network. This means that a telephone call reserves a 64 Kbps physical circuit between the endpoints (caller and callee, or, for data, origin and destination). The full bandwidth is dedicated to the circuit even during periods of the call when no voice or data is transmitted. Obviously, this is a very inefficient way to make a phone call.

Packet switched networks, such as the Internet and corporate LANs divide the message into many small packets. Each packet has a header containing information that enables the switching equipment along the way to route the packet to its final destination (at the destination the header can be used to put the packet in the proper sequence with all of the other packets). Any telecom pipe can run flat out at maximum bandwidth, as a multitude of packets from various messages completely (and therefore efficiently) fill the pipe.

The advantage of packet-switched networks, then, is their highly adept and efficient utilization of network resources. The disadvantage of packet-switched networks, in real-time communications such as voice and visual telephony, has been their variable Quality of Service (QoS), a consequence of network congestion. Telephone network designers have found that callers can tolerate up to about 250 milliseconds (ms) delay before the interval becomes bothersome. Outside of the U.S. (particularly South America) callers appear to tolerate...