Which PBX function is described as mapping a dialed number to a physical extension and ensuring the called line is not busy?

Which PBX function is described as mapping a dialed number to a physical extension and ensuring the called line is not busy?

• A. To establish a connection between two telephones and maintain it for as long as required without interruption or interference.
• B. To map a dialed number to a physical telephone and ensure that the telephone is not already busy.
• C. To provide voicemail services.
• D. To route calls to external networks.

Answer: (B)

The fundamental idea here is how a PBX handles dialing to an internal extension and checks availability before connecting. When you dial a number, the PBX must translate that dialed sequence into the correct physical extension on the system and simultaneously verify that the target line isn’t already in use. This two-part process—mapping the dialed digits to the right extension and performing busy detection (line seizure)—ensures the system connects you to the correct endpoint only when it’s free. If the extension is free, the PBX establishes the path and completes the call; if it’s busy, the call is not connected and you may hear a busy signal or receive an alternate option. The option that describes this behavior precisely matches the core function: it maps the dialed number to a physical telephone and ensures the telephone is not already busy. The other options describe related but different PBX capabilities—establishing and maintaining a general connection, providing voicemail, or routing to external networks—without the specific combination of internal mapping and busy-status checking.

The fundamental idea here is how a PBX handles dialing to an internal extension and checks availability before connecting. When you dial a number, the PBX must translate that dialed sequence into the correct physical extension on the system and simultaneously verify that the target line isn’t already in use. This two-part process—mapping the dialed digits to the right extension and performing busy detection (line seizure)—ensures the system connects you to the correct endpoint only when it’s free. If the extension is free, the PBX establishes the path and completes the call; if it’s busy, the call is not connected and you may hear a busy signal or receive an alternate option.

The option that describes this behavior precisely matches the core function: it maps the dialed number to a physical telephone and ensures the telephone is not already busy. The other options describe related but different PBX capabilities—establishing and maintaining a general connection, providing voicemail, or routing to external networks—without the specific combination of internal mapping and busy-status checking.