Voice-mail - How Voice-mail Works

How Voice-mail Works

This section describes how the original style, standalone, voice-mail system worked with a corporate PBX. The principle is the same with Central Office Switches (CO Switches) or Mobile Telephone Switching Office (MTSOs). More modern voice-mail systems work on the same principle, but some of the components may be shared with other systems, such as email systems.

Voice-mail systems contain several elements shown in the figure below:

• A central processor (CPU) which runs the operating system and a program (software) that gives the system the look-and-feel of a voice-mail system. This software includes thousands of pre-recorded prompts that "speak" to the users as they interact with the system;
• Disk controller and multiple disk drives for message storage;
• System disks which not only include the software above, but also contain a complete directory of all users with pertinent data about each (name, extension number, voice-mail preferences, and pointers to each of the messages stored on the message disk that belong to them);
• Telephone interface system that enables many phone lines to be connected to it.

The drawing below shows how the voice-mail system interacts with the PBX. Suppose an outside caller is calling Fred's extension 2345. The incoming call comes in from the public network (A) and comes into the PBX. The call is routed to Fred's extension (B), but Fred doesn't answer. After a certain number of rings, the PBX stops ringing Fred's extension and forwards the call to an extension connected to the voice-mail system (C). It does this because PBXs are generally programmed to forward busy or unanswered calls to another extension. Simultaneously the PBX tells the voice-mail system (through signaling link D) that the call it is forwarding to voice-mail is for Fred at extension 2345. In this way, the voice-mail system can answer the call with Fred's greeting.

There are many microprocessors throughout the system since the system must handle large amounts of data and it's unacceptable to have any wait times (for example, when the system is recording or playing your message, it's unacceptable if the system stops recording momentarily like computers often do while accessing large files).

When Fred's extension forwards to the voice-mail system, the Telephone Interface detects ringing. It signals to the Central Processor (CPU) that a call is coming in. The CPU simultaneously receives a signal on the PBX-Voice-mail Data Link (D) telling it that extension 2345 is being forwarded on ring-no-answer to the specific extension that is now ringing. The CPU directs the Telephone Interface (which controls the line interface cards) to answer the call. The CPU's program realizes that it's a call for Fred so it looks up Fred's greeting immediately and directs the Disk Controller to start playing it to the caller. It also plays some system prompts instructing the caller what comes next (for example, "When you have finished recording, you may hang up or press ‘#' for more options"). All "talking" to the caller is done through prompts that are selected by the CPU according to the program stored in the voice-mail system. The CPU selects the prompts in response to the keys the caller presses.

The caller's message is digitized by the Telephone Interface system and transmitted to the Disk Controller for storage onto the Message Disks. Some voice-mail systems will scramble the message for further security. The CPU then stores the location of that message in the System Disk inside Fred's mailbox directory entry. After the caller hangs up and the message has been stored, the CPU sends a signal to the PBX through the link (D) instructing the PBX to turn on the message waiting light on Fred's phone.

When Fred comes back to his desk and sees the light on his phone, he calls a designated extension number for the voice-mail system (an actual extension number assigned to the lines in "C" in the figure above).

Again the Telephone Interface alerts the CPU that a call is coming in on a particular line, but this time the signaling from the PBX-Voice-mail Data Link (D) indicates that Fred is calling directly, not being forwarded. The CPU directs the Telephone Interface to answer the call.

Since the CPU "knows" it is Fred (from the signaling on the Data Link D), it looks up Fred's information on the System Disk, specifically his password. The CPU then directs Disk Controller to play a log-on prompt to the user: "Please enter your password." Once the password is entered (via Touch-tones), the CPU compares it to the correct one and, if entered correctly, allows Fred to continue.

The CPU then determines (from Fred's directory entry) that Fred has a new message. The CPU then presents Fred his options (e.g., "You have a new message. To listen to your new message, press 1; to record a message, press 2" etc.) The options are presented by the CPU directing the Disk Controller to play prompts, and the CPU listens for Touch-tones from Fred. This interaction of playing prompts and responding with Touch-tones enables Fred to interact with the voice-mail system easily.

If Fred presses 1 to listen to his message, the CPU looks up the location of Fred's new message in his mailbox directory (on the System Disk), and directs the Disk Controller to play that message. The Disk Controller finds the message on the Message Disks, and sends the data stream directly to the Telephone Interface. The Telephone Interface then converts the data stream to sound and plays it to Fred through the Line Interface Card which Fred is connected to.

Playback controls (like rewind, pause, fast forward, changing volume, etc.) are all input via Touch-tones, are "read" by the CPU, and the appropriate actions are taken based on the stored program in the system. For example, if Fred wants to pause message playback, he might press 2. Since the CPU is constantly listening for Touch-tones from Fred, his command causes the CPU to direct the Disk Controller to stop playing the message. A variety of playback controls and options are available on most sophisticated voice-mail systems so that users can control message playback, store messages in archives, send messages to groups, change their preferences, etc.

The better designed voice-mail systems have a user-friendly interface with clear and meaningful prompts so the interaction with the voice-mail system is quick and easy.