3.5.3 Traditional vs. IP-Based PBX Systems

The private branch exchange (PBX) is, in large part, to telephony what Network Address Translation (NAT) is to IP networking. While they are not exact equivalents, the PBX systems do allow you to run a private network of telephones with features similar to those of the PSTN or POTS networks. You will need to understand the basic features and components of TDM, IP, and hybrid PBX systems for the Convergence+ examination.

In addition to the PBX systems, another telephone system type known as a key system is available. This telephone solution is not covered in the Convergence+ objectives and will not be covered here in detail. A key system uses telephones with multiple buttons, or “keys,” and lights that indicate which lines are in use. Someone who wants to place a call just presses a button to select a line and begins dialing. Each line will connect the user directly with the telephone company’s central office for a dial tone. The hybrid PBX solution referenced in the Convergence+ exam refers to a TDM and IP combined PBX and not to a key system/PBX combination. Table 7-1 provides a comparison of PBX systems and key systems.